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Detailed Chapter 5 Acids Bases and Salts MSBSHSE Solutions for Class 9 Science
For Class 9 students, solving MSBSHSE textbook questions is the most effective way to build a strong conceptual foundation. Our Class 9 Science solutions follow a detailed, step-by-step approach to ensure you understand the logic behind every answer. Practicing these Chapter 5 Acids Bases and Salts solutions will improve your exam performance.
Class 9 Science Chapter 5 Acids Bases and Salts MSBSHSE Solutions PDF
Std 9 Science Chapter 5 Acids, Bases And Salts Question Answer Maharashtra Board
Class 9 Science Chapter 5 Acids, Bases And Salts Question Answer Maharashtra Board
Question 1. Identify the odd one out and justify.
(a) Chloride, nitrate, hydride, ammonium
Answer: Ammonium is the odd one out as it is a basic radical and rest all are acidic radicals. Generally, basic radicals are formed by the removal of electrons from the atom of metals such as Na+, Cu2+. But there are some exceptions, such as NH4+.
In simple words: Ammonium is the odd one out because it is a basic radical, while chloride, nitrate, and hydride are acidic radicals. Basic radicals usually form when metals lose electrons.
🎯 Exam Tip: Understanding the classification of radicals as acidic or basic is key to solving such identification questions. Focus on the nature of the ion (metal or non-metal origin) and its typical charge.
(b) Hydrogen chloride, sodium hydroxide, calcium oxide, ammonia
Answer: Hydrogen chloride is the odd one out. It is acidic and rest all are basic.
In simple words: Hydrogen chloride is the odd one because it is an acid, whereas sodium hydroxide, calcium oxide, and ammonia are all bases.
🎯 Exam Tip: Identify the chemical nature (acid or base) of each compound. Acids release H+ ions, while bases typically release OH- ions or accept H+ ions.
(c) Acetic acid, carbonic acid, hydrochloric acid, nitric acid
Answer: Carbonic acid is the odd one out. It is a dibasic acid and rest are all monobasic acids.
In simple words: Carbonic acid is the odd one because it is a dibasic acid (can donate two protons), while acetic acid, hydrochloric acid, and nitric acid are monobasic acids (can donate one proton).
🎯 Exam Tip: Basicity of an acid refers to the number of H+ ions it can furnish per molecule. Counting the dissociable hydrogen atoms helps classify acids.
(d) Ammonium chloride, sodium chloride, potassium nitrate, sodium sulphate
Answer: Ammonium chloride is the odd one out, as it is made up of a strong acid and weak base and rest all are formed from strong acid and strong base.
In simple words: Ammonium chloride is the odd one out because it's formed from a strong acid and a weak base, making it an acidic salt, while the others are neutral salts formed from strong acids and strong bases.
🎯 Exam Tip: The nature of a salt (acidic, basic, or neutral) depends on the strength of the acid and base from which it is derived. Strong acid + weak base yields an acidic salt.
(e) Sodium nitrate, sodium carbonate, sodium sulphate, sodium chloride
Answer: Sodium carbonate is the odd one out, as it is made up of a weak acid and strong base, and rest all are formed from strong acid and strong base.
In simple words: Sodium carbonate is the odd one because it's a basic salt, formed from a weak acid and a strong base, while the other listed compounds are neutral salts from strong acids and strong bases.
🎯 Exam Tip: Salts formed from weak acids and strong bases hydrolyze to produce OH- ions, making their solutions basic. Conversely, strong acid + strong base salts are neutral.
(f) Calcium oxide, magnesium oxide, zinc oxide, sodium oxide.
Answer: Zinc oxide is the odd one out, as it is an amphoteric oxide, and rest all are basic oxides.
In simple words: Zinc oxide is the odd one here because it can act as both an acid and a base (amphoteric), while calcium oxide, magnesium oxide, and sodium oxide are all basic oxides.
🎯 Exam Tip: Amphoteric oxides react with both acids and bases to form salts and water. This dual nature distinguishes them from purely basic or acidic oxides.
(g) Crystalline blue vitriol, crystalline common salt, crystalline ferrous sulphate, crystalline sodium carbonate.
Answer: Crystalline common salt is the odd one out, as it does not contain water of crystallisation. It is an ionic compound and ionic compounds are crystalline in nature and rest all have their crystalline structure because of their water of crystallization.
In simple words: Crystalline common salt is the odd one because, unlike blue vitriol, ferrous sulphate, and sodium carbonate, it does not contain water of crystallization within its crystal structure.
🎯 Exam Tip: Water of crystallization refers to water molecules chemically bound within crystal structures. Many ionic compounds form hydrates with specific amounts of water.
(h) Sodium chloride, potassium hydroxide, acetic acid, sodium acetate.
Answer: Acetic acid is the odd one out. It is an acid, the rest are all salts.
In simple words: Acetic acid is the odd one out because it's an acid, while sodium chloride, potassium hydroxide (though a base, is in the context of salts, so comparing its role), and sodium acetate are salts. (Correction in original text: Potassium hydroxide is a base, not a salt. If comparing to "salts", acetic acid is the clear odd one as an acid). Let's re-evaluate. Sodium chloride is a salt. Sodium acetate is a salt. Acetic acid is an acid. Potassium hydroxide is a base. So, acetic acid is the only acid. Therefore, it is the odd one out.
🎯 Exam Tip: Accurately classifying compounds as acids, bases, or salts is fundamental. Acids release H+; bases release OH- or accept H+; salts are ionic compounds formed from acid-base reactions.
Question 2. Write down the changes that will be seen in each instance and explain the reason behind it.
(a) 50ml water is added to 50ml solution of copper sulphate.
Answer:
• Copper sulphate solution is blue. It is a concentrated solution.
• When 50 ml of water is added to this concentrated solution, it becomes a diluted solution.
• The intensity of the blue colour is now different in this homogenous mixture.
In simple words: When water is added to a concentrated blue copper sulphate solution, it becomes diluted, and its blue color appears less intense because the concentration of copper sulphate decreases.
🎯 Exam Tip: Dilution reduces the concentration of solute in a solution, which often manifests as a lighter color in colored solutions. Homogeneous mixtures have uniform composition throughout.
(b) Two drops of the indicator phenolphthalein were added to 10ml solution of sodium hydroxide.
Answer:
• Sodium hydroxide is a base and phenolphthalein is a synthetic indicator.
• Sodium hydroxide solution will turn pink if phenolphthalein is added to it.
• It is a test for identifying bases.
In simple words: When phenolphthalein is added to sodium hydroxide solution, the solution turns pink, as phenolphthalein is an indicator that turns pink in basic solutions. This confirms the presence of a base.
🎯 Exam Tip: Indicators like phenolphthalein change color at specific pH ranges, making them useful for identifying acidic or basic solutions. Phenolphthalein is colorless in acid and pink in base.
(c) Two or three filings of copper were added to 10ml dilute nitric acid and stirred.
Answer: When copper metal reacts with dilute nitric acid, the metal does not displace hydrogen from the acid like reaction with other metals. Instead the reaction produces nitric oxide, (NO).
\(3 Cu_{(s)} + 8 HNO_{3(aq)}\)
\(\implies 3 Cu (NO_3)_{2 (aq)} + 2 NO_{(g)} + 4 H_2O_{(l)}\)
Copper + nitric acid (dil.) \(\implies\) copper + nitrate + nitric oxide + water
In simple words: Copper reacts with dilute nitric acid to produce copper nitrate, nitric oxide gas, and water. Unlike more reactive metals, copper doesn't simply displace hydrogen but instead gets oxidized, producing nitric oxide.
🎯 Exam Tip: Remember that not all metals react with acids to liberate hydrogen gas. Less reactive metals, like copper, react differently with oxidizing acids such as nitric acid, producing nitrogen oxides instead.
(d) A litmus paper was dropped into 2ml dilute HCl. Then 2ml concentrated NaOH was added to it and stirred.
Answer:
Blue litmus Paper:
• HCl is hydrochloric acid, so the blue litmus turns red.
• When equal amount of NaOH is added the colour again changes to blue and remains the same.
Red litmus paper:
• Red litmus paper shows no colour change in hydrochloric acid.
• When some amount of NaOH is added the colour changes to blue initially
• but when the amount of NaOH is sufficient the blue colour dissappears.
• Equal amounts of HCl and NaOH results in the formation of NaCl, a salt, and the solvent water. This reaction is called the neutralization reaction.
In simple words: Blue litmus turns red in HCl. Adding NaOH first causes the red litmus to turn blue (neutralization/excess base), then with equal amounts, it becomes neutral, and the blue color persists or if carefully neutralized, it might become blue again. Red litmus stays red in HCl, turns blue with NaOH, and then returns to red if excess HCl is added. Neutralization forms salt and water.
🎯 Exam Tip: Litmus paper indicates pH changes: blue turns red in acid, red turns blue in base. Neutralization reactions involve an acid and a base reacting to form a salt and water, bringing the pH closer to 7.
(e) Magnesium oxide was added to dilute HCl and magnesium oxide was a added to dilute NaOH.
Answer:
(i) Magnesium oxide + dil HCl.
This is a neutralization reaction. Magnesium oxide is an insoluble base, it reacts with dilute HCl to produce a soluble salt MgCl2 and water H2O.
\(MgO_{(s)} + 2HCl_{(aq)}\)
\(\implies MgCl_{2(aq)} + H_2O_{(l)}\)
(ii) Magnesium oxide + NaOH.
No chemical reaction takes place between magnesium oxide and sodium hydroxide.
In simple words: Magnesium oxide, a basic oxide, reacts with dilute HCl to form magnesium chloride and water (neutralization). However, it does not react with dilute NaOH because both are basic in nature.
🎯 Exam Tip: Basic oxides react with acids, but typically not with other bases. Amphoteric oxides are an exception, reacting with both acids and strong bases.
(f) Zinc oxide was added to dilute HCl and zinc oxide was added to dilute NaOH.
Answer:
• Zinc oxide reacts with dilute hydrochloric acid to form zinc chloride and water. It is a neutralization reaction.
\(ZnO_{(s)} + 2HCl_{(aq)}\)
\(\implies ZnCl_{2(aq)} + H_2O_{(l)}\)
• Zinc oxide reacts with sodium hydroxide to form sodium zincate and water.
\(ZnO_{(s)} + 2NaOH_{(aq)}\)
\(\implies Na_2ZnO_{2(aq)} + H_2O_{(l)}\)
In simple words: Zinc oxide reacts with dilute HCl to form zinc chloride and water, and also reacts with sodium hydroxide to form sodium zincate and water. This dual reactivity shows that zinc oxide is an amphoteric oxide.
🎯 Exam Tip: This example highlights the amphoteric nature of zinc oxide, meaning it can act as both an acid and a base, reacting with both strong acids and strong bases.
(g) Dilute HCl was added to limestone.
Answer:
• When hydrochloric acid is added to limestone, carbon dioxide is liberated. Limestone is calcium carbonate.
\(CaCO_3 + 2 HCl \implies CaCl_2 + CO_2 + H_2O\)
• Carbon dioxide is prepared in the laboratory using these chemicals.
In simple words: When dilute HCl is added to limestone (calcium carbonate), carbon dioxide gas is released, along with the formation of calcium chloride and water. This reaction is a common lab method for producing CO2.
🎯 Exam Tip: Metal carbonates and bicarbonates react with acids to produce salt, water, and carbon dioxide gas. The evolution of CO2 can be tested with limewater.
(h) Pieces of blue vitriol were heated in a test tube. On cooling, water was added to it.
Answer:
• On heating, the crystalline structure of blue vitriol breaks down to form a colourless powder and water is released.
• This water is part of the crystal structure of blue vitriol.
• It is called water of crystallization.
• On adding water to the white powder, a solution was formed which has the same colour as the copper sulphate salt solution.
In simple words: Heating blue vitriol (hydrated copper sulphate) removes its water of crystallization, turning it into a colorless powder. Adding water back restores its original blue color, showing it's a reversible physical change.
🎯 Exam Tip: Water of crystallization is responsible for the characteristic color and crystalline shape of many hydrated salts. Its removal often leads to a change in color and crystal structure, which can be reversed by rehydration.
(i) Dilute H2SO4 was taken in an electrolytic cell and electric current was passed through it.
Answer:
• If pure water is used in the electrolytic cell, current does not flow even on putting on the switch.
• Pure water is a bad conductor of electricity. Dilute H2SO4 is acidulated water.
• The electrical conductivity of water increases on mixing with strong acid or base in it due to their dissociation and electrolysis of water takes place.
• \(H_2SO_4\) is fully dissociated in aqueous solution. \(H_2SO_4 \implies 2H^+ + SO_4^{2-}\)
• H2O is a weak electrolyte and is only slightly dissociated
\(H_2O \implies H^+ + OH^-\)
• During electrolysis, the hydrogen ions migrate towards the cathode and are discharged there.
[H+ ions gains electrons and are converted to hydrogen gas]
\(2H^+ + 2e^- \implies H_{2(g)}\)
Cathode reaction:
\(2H_2O_{(l)} + 2e^- \implies H_{2(g)} + 2OH_{(aq)}^-\)
Anode reaction:
\(2H_2O_{(l)} \implies O_{2(g)} + 4H_{(aq)}^+ + 4e^-\)
• For every hydrogen ion discharged at the anode, another hydrogen ion is formed at the cathode.
• The net result is that the concentration of the sulphuric acid remains constant and electrolysis of water is overall reaction. \(2H_2O \implies 2H_2 + O_2\)
• The volume of the hydrogen gas formed near the cathode is double that of the oxygen gas formed near the anode.
In simple words: When electric current is passed through dilute H2SO4, water undergoes electrolysis, decomposing into hydrogen gas at the cathode and oxygen gas at the anode. The sulfuric acid acts as an electrolyte, increasing water's conductivity.
🎯 Exam Tip: Remember that pure water is a poor conductor; adding an acid or base (electrolyte) is necessary for electrolysis. The volume ratio of hydrogen to oxygen produced during water electrolysis is 2:1.
Question 3. Classify the following oxides into three types and name the types. CaO, MgO, CO2, SO3, Na2O, ZnO, Al2O3, Fe2O3
Answer:
There are three types of oxides : Basic oxides, Acidic oxides and Amphoteric oxides.
| Basic oxides | Acidic oxides | Amphoteric oxides |
|---|---|---|
| CaO | CO2 | ZnO |
| MgO | SO3 | Al2O3 |
| Na2O | ||
| Fe2O3 |
Generally metal oxides are basic in nature.
Exception: Al2O3 and ZnO are amphoteric oxides.
Generally non-metal oxides are acidic in nature.
In simple words: Oxides are classified into basic (metal oxides like CaO, MgO, Na2O, Fe2O3), acidic (non-metal oxides like CO2, SO3), and amphoteric (oxides like ZnO, Al2O3 that react as both acid and base).
🎯 Exam Tip: Metal oxides are typically basic, non-metal oxides are acidic, and some oxides (like those of zinc and aluminum) exhibit amphoteric behavior, reacting with both acids and bases.
Question 4. Explain by drawing a figure of the electronic configuration.
a. Formation of sodium chloride from sodium and chlorine.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र सोडियम और क्लोरीन परमाणुओं से सोडियम क्लोराइड के निर्माण की इलेक्ट्रॉनिक विन्यास प्रक्रिया को दर्शाता है। सोडियम परमाणु (2, 8, 1) अपना बाहरी इलेक्ट्रॉन क्लोरीन परमाणु (2, 8, 7) को स्थानांतरित करता है, जिससे सोडियम धनायन (2, 8) और क्लोराइड ऋणायन (2, 8, 8) बनते हैं। इन विपरीत आवेशित आयनों के बीच स्थिर वैद्युत आकर्षण से NaCl का निर्माण होता है।
In simple words: Sodium chloride forms when a sodium atom donates its outermost electron to a chlorine atom, creating positively charged sodium ions and negatively charged chloride ions, which are then held together by electrostatic forces.
🎯 Exam Tip: Ionic bond formation involves the complete transfer of electrons from a metal (forming a cation) to a non-metal (forming an anion), leading to stable electron configurations (octets).
b. Formation of a magnesium chloride from magnesium and chlorine.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र मैग्नीशियम और क्लोरीन परमाणुओं से मैग्नीशियम क्लोराइड के निर्माण की इलेक्ट्रॉनिक विन्यास प्रक्रिया को दर्शाता है। मैग्नीशियम परमाणु (2, 8, 2) अपने दो बाहरी इलेक्ट्रॉनों को दो अलग-अलग क्लोरीन परमाणुओं (प्रत्येक 2, 8, 7) को स्थानांतरित करता है, जिससे मैग्नीशियम धनायन (2+, 2, 8) और दो क्लोराइड ऋणायन (प्रत्येक 2, 8, 8) बनते हैं। इन आयनों के बीच के आकर्षण से MgCl2 बनता है।
In simple words: Magnesium chloride forms when a magnesium atom donates its two valence electrons, one to each of two separate chlorine atoms, resulting in a magnesium cation and two chloride anions held by ionic bonds.
🎯 Exam Tip: For ionic compounds, metals achieve stable electron configurations by losing electrons, and non-metals achieve stability by gaining electrons. The number of electrons transferred ensures electrical neutrality of the compound.
Question 5. Show the dissociation of the following compounds on dissolving in water, with the help of chemical equation and write whether the proportion of dissociation is small or large. Hydrochloric acid, Sodium chloride, Potassium hydroxide, Ammonia, Acetic acid, Magnesium chloride, Copper sulphate.
(a) Hydrochloric acid (HCl)
Answer:
• \(HCl_{(g)} \xrightarrow{\text{Water dissociation}} H_{(aq)}^+ + Cl_{(aq)}^-\)
• Hydrochloric acid is a strong acid, as on dissolving in water, it dissociates almost completely and the resulting aqueous solution contains mainly H+ ions and the concerned acidic radical.
• The proportion of dissociation is large.
In simple words: Hydrochloric acid dissociates almost completely in water, producing a large proportion of H+ and Cl- ions. This makes it a strong acid.
🎯 Exam Tip: Strong acids and bases dissociate almost completely in water, leading to a high concentration of ions and thus large proportions of dissociation. This impacts their conductivity and reactivity.
(b) Sodium chloride (NaCl)
Answer:
• \(NaCl_{(s)} \xrightarrow{\text{Water dissociation}} Na_{(aq)}^+ + Cl_{(aq)}^-\)
• When an ionic compound begins to dissolve in water, the water molecules push themselves in between the positive and negative ions of the compound and separate them from each other.
• The proportion of dissociation is large.
In simple words: Sodium chloride dissolves in water, separating into Na+ and Cl- ions due to water molecules surrounding and pulling them apart. The proportion of dissociation is large because it's an ionic compound.
🎯 Exam Tip: Ionic compounds generally dissociate completely into their constituent ions when dissolved in water, making them strong electrolytes and resulting in a large proportion of dissociation.
(c) Potassium hydroxide (KOH)
Answer:
• \(KOH_{(l)} \xrightarrow{\text{Water dissociation}} K_{(aq)}^+ + OH_{(aq)}^-\)
• Potassium hydroxide is a strong base, as on dissolving in water, it dissociates almost completely and the resulting aqueous solution contains mainly OH- ions and the concerned basic radical.
• The proportion of dissociation is large.
In simple words: Potassium hydroxide is a strong base that almost completely dissociates in water, yielding a high proportion of K+ and OH- ions in its aqueous solution.
🎯 Exam Tip: Similar to strong acids, strong bases also show a large proportion of dissociation in water, contributing significantly to the hydroxide ion concentration and making them strong electrolytes.
(d) Ammonia (NH3)
Answer:
(i) \(NH_{3(g)} + H_2O_{(l)} \xrightarrow{\text{Water dissociation}} NH_{4(aq)}^+ + OH_{(aq)}^-\)
(ii) Ammonia dissolves in water to form NH4OH (ammonium hydroxide). NH4OH does not dissociate completely as it is a weak base. The aqueous solution contains a small proportion of OH- ions and the concerned basic radical along with a large proportion of undissociated molecules of the base i.e. NH4OH.
(iii) The proportion of dissociation is small.
In simple words: Ammonia dissolves in water to form ammonium hydroxide, which is a weak base. It dissociates only partially, resulting in a small proportion of NH4+ and OH- ions and many undissociated molecules.
🎯 Exam Tip: Weak acids and bases dissociate only partially in water, meaning a significant portion of the molecules remains undissociated. This results in a small proportion of dissociation and weaker electrolytic properties.
(e) Acetic acid (CH3COOH)
Answer:
• \(CH_3COOH_{(l)} \xrightarrow{\text{Water dissociation}} CH_3COO_{(aq)}^- + H_{(aq)}^+\)
• Acetic acid is a weak acid, on dissolving in water it does not dissociate completely, and the resulting aqueous solution contains H+ ion and the concerned acidic radical in small proportion along with large proportion of the undissociated molecules of the acid.
• The proportion of dissociation is small.
In simple words: Acetic acid is a weak acid that dissociates only slightly in water, forming a small proportion of H+ and acetate ions while most of the molecules remain undissociated.
🎯 Exam Tip: For weak acids, the equilibrium lies towards the undissociated molecules, resulting in a low concentration of H+ ions and a small proportion of dissociation. This distinguishes them from strong acids.
(f) Magnesium chloride (MgCl2)
Answer:
• \(MgCl_{2(s)} \xrightarrow{\text{Water dissociation}} Mg_{(aq)}^{2+} + 2Cl_{(aq)}^-\)
• Magnesium chloride dissolves in water and forms magnesium ions and chloride ions. When an ionic compound begins to dissolve in water, the water molecules push themselves in between the ions of the compound and separate them from each other.
• The proportion of dissociation is large.
In simple words: Magnesium chloride, an ionic compound, dissolves and dissociates almost completely in water, producing a large proportion of Mg2+ and Cl- ions due to the interaction with water molecules.
🎯 Exam Tip: Most soluble ionic compounds, when dissolved in water, dissociate completely into their constituent cations and anions, leading to a large proportion of dissociation and high electrical conductivity.
(g) Copper sulphate (CuSO4)
Answer:
• \(CuSO_{4(s)} \xrightarrow{\text{Water dissociation}} Cu_{(aq)}^{2+} + SO_{4(aq)}^{2-}\)
• When Copper sulphate is dissolved in water it forms copper ions and sulphate ions. When an ionic compound begins to dissolve in water, the water molecules push themselves in between the ions of the compound and separate them from each other.
• The proportion of dissociation is large.
In simple words: Copper sulphate dissolves in water, where water molecules separate its copper and sulphate ions, leading to a large proportion of dissociation typical for ionic compounds.
🎯 Exam Tip: Ionic compounds dissolve in water through a process called solvation, where polar water molecules surround and stabilize the separated ions, promoting complete dissociation.
Question 6. Write down the concentration of each of the following solutions in g/L and mol/L.
a. 7.3g HCl in 100ml solution
b. 2g NaOH in 50ml solution
c. 3g CH3COOH in 100ml solution
d. 4.9g H2SO4 in 200ml solution
Answer:
To find : The concentration in g/L.
Solution:
| Solute | Quantity of solute | Volume of Solution | Concentration of the solution | ||||
|---|---|---|---|---|---|---|---|
| A | B | C | D = C / Molecular mass (u) | E | F = C / E | G = D / E | |
| Name | Molecular formula | Molecular mass (u) | Gram (g) | Mole (mol) | Litre (L) | Gram/ Litre (g/L) | Molarity (M) mole/litre (mol/L) |
| Hydrochloric acid | HCl | 36.5 u | 7.3 g | 0.2 mol | 100 ml = 0.1L | 73 g/L | 2 mol/L |
| Sodium Hydroxide | NaOH | 40 u | 2.0 g | 0.05 mol | 50 ml = 0.05L | 40 g/L | 1 mol/L |
| Acetic Acid | CH3COOH | 60 u | 3.0 g | 0.05 mol | 100 ml = 0.1L | 30 g/L | 0.5 mol/L |
| Sulphuric acid | H2SO4 | 98 u | 4.9 g | 0.05 mol | 200 ml = 0.2L | 24.5 g/L | 0.25 mol/L |
In simple words: To calculate concentration, first find grams per liter by dividing the mass of solute by solution volume in liters. Then, calculate moles per liter (molarity) by dividing moles of solute by solution volume in liters, using the molecular mass to convert grams to moles.
🎯 Exam Tip: Remember the formulas: Concentration (g/L) = Mass of solute (g) / Volume of solution (L) and Molarity (mol/L) = Moles of solute (mol) / Volume of solution (L). Pay attention to unit conversions (ml to L).
Question 7. Obtain a sample of rainwater. Add to it a few drops of universal indicator. Meausre its pH. Describe the nature of the sample of rainwater and explain the effect if it has on the living world.
Answer:
• pH of rain water is 6.5 that means rain water is slightly acidic.
• When we add universal indicator to rain water it turns orangish red, indicating pH value is between 0 to 7, which tells us that rain water is acidic in nature.
• Most of the plants grow best when pH of soil is close to 7. If the soil is too acidic or too basic, it affects plant growth.
In simple words: Normal rainwater has a slightly acidic pH (around 6.5) due to dissolved CO2; a universal indicator would show an orangish-red color. If it becomes too acidic (acid rain), it can harm plant growth by altering soil pH, which is crucial for nutrient availability.
🎯 Exam Tip: The pH of rainwater is naturally slightly acidic (around 5.6-6.5) due to dissolved carbon dioxide. Acid rain (pH below 5.6) is harmful to the environment as it affects soil fertility and aquatic life by changing the pH.
Question 8. Answer the following questions.
a. Classify the acids according to their basicity and give one example of each type.
Answer:
• Basicity of acids : The number of H+ ions obtainable by the dissociation of one molecule of an acid is called its basicity. The acids are classified as monobasic, dibasic and tribasic acids based on the number of H+ ions present.
• Examples of monobasic acid : HCl, HNO3, CH3COOH
• Examples of dibasic acid: H2SO4, H2CO3
• Examples of tribasic acid: H3BO3, H3PO4
In simple words: Acids are classified by basicity, which is the number of H+ ions they release per molecule. Monobasic acids (like HCl) release one, dibasic acids (like H2SO4) release two, and tribasic acids (like H3PO4) release three H+ ions.
🎯 Exam Tip: Basicity is determined by the number of ionizable hydrogen atoms in an acid molecule. Correctly identifying these allows for proper classification into monobasic, dibasic, or tribasic acids.
b. What is meant by neutralization? Give two examples from everyday life of the neutralization reaction.
Answer:
• In neutralization reaction, an acid reacts with a base to form salt and water.
• In a neutralisation reaction the acid dissociates to form H+ ions and base dissociates to form OH ions.
• They combine to form H2O molecules which mixes with the solvent.
Examples in daily life:
• When people suffer from acidity, they take some antacids to neutralise the acid in their stomach.
• If an ant stings us the pain is due to formic acid. It is neutralised by rubbing moist baking soda which is basic in nature.
In simple words: Neutralization is a chemical reaction where an acid and a base react to form a salt and water. Common examples include taking antacids for stomach acidity and using baking soda to relieve ant sting pain.
🎯 Exam Tip: Neutralization is a key concept in acid-base chemistry. Its application in everyday life, such as using antacids or treating insect stings, demonstrates its practical importance.
c. Explain what is meant by electrolysis of water. Write the electrode reactions and explain them.
Answer:
Electrolysis of water:
• Electrolysis of water is the decomposition of water into oxygen and hydrogen gas due to an electric current being passed through acidified water.
• Cathode reaction:
\(2H_2O_{(l)} + 2e^- \implies H_{2(g)} + 2OH_{(aq)}^-\)
• Anode reaction:
\(2H_2O_{(l)} \implies O_{2(g)} + 4H_{(aq)}^+ + 4e^-\)
• It is found that the volume of gas formed near the cathode is double that of the gas formed near the anode.
• Hydrogen gas is formed near the cathode and oxygen gas near the anode.
• From this, it is clear that electrolysis of water has taken place and its constituent element have been released.
In simple words: Electrolysis of water is the process of breaking down water into hydrogen and oxygen gases using an electric current, typically in acidified water. Hydrogen forms at the negative electrode (cathode) and oxygen at the positive electrode (anode), with hydrogen volume being double that of oxygen.
🎯 Exam Tip: For electrolysis of water, remember the balanced half-reactions at the anode and cathode, and the 2:1 volume ratio of hydrogen gas to oxygen gas produced, which is consistent with water's H2O formula.
Question 9. Give a reason for the following.
a. Hydronium ions are always in the form H3O+.
Answer:
• Acids in water gives H+ ions. These H+ ions do not exist freely in water.
• This is because H⁺ is a single proton, a hydrogen atom has only one proton and one electron.
• If the electron is removed to make H+, all that is left is an extremely tiny positively charged nucleus.
• This H ion will immediately combine with the surrounding water (H2O) molecules to form (H3O+) hydronium ion.
In simple words: H+ ions, being just a proton, are highly unstable and cannot exist freely in water. Instead, they immediately combine with water molecules to form stable hydronium ions (H3O+).
🎯 Exam Tip: Always represent hydrogen ions in aqueous solutions as hydronium ions (H3O+) because a bare proton (H+) is too reactive to exist independently and readily associates with water molecules.
b. Buttermilk spoils if kept in a copper or brass container.
Answer:
• Buttermilk contains an organic acid called as lactic acid.
• The lactic acid reacts with copper and brass and forms toxic compounds which are not fit for consumption.
• They are harmful and may cause food poisoning.
• So it is not advisable to keep buttermilk in brass or copper containers.
In simple words: Buttermilk, containing lactic acid, spoils in copper or brass containers because the acid reacts with the metals to form toxic compounds that are harmful for consumption.
🎯 Exam Tip: Acids react with metals (especially reactive ones) to form salts and hydrogen gas. In food contexts, this reaction can produce harmful substances, making certain metal containers unsuitable for acidic foods.
Question 10. Write the chemical equations for the following activities.
(a) NaOH solution was added to HCl solution.
Answer:
When NaOH reacts with HCl, it gives NaCl and water.
\(NaOH_{(aq)} + HCl_{(aq)}\)
\(\implies NaCl_{(aq)} + H_2O_{(l)}\)
Sodium hydroxide + Hydrochloric acid \(\implies\) Sodium chloride + Water
In simple words: Sodium hydroxide (a base) reacts with hydrochloric acid to form sodium chloride (a salt) and water. This is a classic neutralization reaction.
🎯 Exam Tip: Neutralization reactions between strong acids and strong bases always yield a neutral salt and water. Ensure the equation is balanced and state symbols are correct.
(b) Zinc dust was added to dilute H2SO4.
Answer:
When zinc reacts with dilute sulphuric acid, it forms zinc sulphate and hydrogen gas is liberated.
\(Zn_{(s)} + H_2SO_{4 (aq)}\)
\(\implies ZnSO_{4(aq)} + H_{2 (g)}\)
Zinc + Sulphuric acid \(\implies\) Zinc sulphate + Hydrogen
In simple words: Zinc metal reacts with dilute sulphuric acid to produce zinc sulphate and liberate hydrogen gas. This is a single displacement reaction where zinc is more reactive than hydrogen.
🎯 Exam Tip: More reactive metals, like zinc, react with acids to displace hydrogen, forming a salt and hydrogen gas. Remember to balance the chemical equation.
(c) Dilute nitric acid was added to calcium oxide.
Answer:
When dilute nitric acid reacts with calcium oxide, it forms calcium nitrate and water.
\(2HNO_{3(aq)} + CaO_{(s)}\)
\(\implies Ca(NO_3)_{2 (aq)} + H_2O_{(l)}\)
dil nitric acid + calcium oxide \(\implies\) calcium nitrate + water
In simple words: Dilute nitric acid reacts with calcium oxide (a basic oxide) to form calcium nitrate and water. This is a neutralization reaction between an acid and a base.
🎯 Exam Tip: Basic oxides react with acids to form salt and water, which is a type of neutralization reaction. Always check if the oxide is acidic, basic, or amphoteric to predict its reaction with acids or bases.
(e) Carbon dioxide gas was passed through KOH solution.
Answer:
When carbon dioxide reacts with potassium hydroxide, it forms potassium carbonate and water.
\(CO_{2(g)} + 2KOH_{(aq)}\)
\(\implies K_2CO_{3(aq)} + H_2O_{(l)}\)
Carbon dioxide + Potassium hydroxide \(\implies\) Potassium carbonate + Water
In simple words: Carbon dioxide, an acidic oxide, reacts with potassium hydroxide (a base) to form potassium carbonate and water. This is an acid-base reaction.
🎯 Exam Tip: Non-metal oxides are generally acidic. They react with bases to form a salt and water, similar to an acid-base neutralization. This reaction is important in industrial gas scrubbing.
(f) Dilute HCl was poured on baking soda.
Answer:
When sodium bicarbonate reacts with hydrochloric acid, it forms sodium chloride, carbon dioxide and water.
\(NaHCO_{3(s)} + HCl_{(aq)}\)
\(\implies NaCl_{(aq)} + CO_{2 (g)} + H_2O_{(l)}\)
Sodium bicarbonate + Hydrochloric acid \(\implies\) Sodium chloride + Carbon dioxide + Water
In simple words: When dilute hydrochloric acid is poured on baking soda (sodium bicarbonate), it reacts to produce sodium chloride, carbon dioxide gas, and water. This reaction is evident by the fizzing (CO2 release).
🎯 Exam Tip: Reactions of acids with bicarbonates or carbonates always produce carbon dioxide gas, a salt, and water. This is a characteristic test for identifying acids and carbonates.
Question 11. State the differences.
a. Acids and bases
Answer:
| Acids | Bases |
|---|---|
| (i) A substance which liberates H+ ions when dissolved in water is an acid | A substance which liberates OH- ions when dissolved in water is called a base. |
| (ii) Blue litmus turns red in an acid. | Red litmus turns blue in a base |
| (iii) The pH of an acid is less than 7. | The pH of a base is greater than 7. |
| (iv) Acids are sour to taste | Bases are bitter to taste, |
| (v) e.g. HCl, H2SO4 | e.g. NaOH, KOH. |
In simple words: Acids release H+ ions, turn blue litmus red, have a pH below 7, and taste sour, like HCl. Bases release OH- ions, turn red litmus blue, have a pH above 7, and taste bitter, like NaOH.
🎯 Exam Tip: Key distinguishing properties of acids and bases include their effect on indicators (litmus), pH values (below 7 for acids, above 7 for bases), and the types of ions they produce in water (H+ for acids, OH- for bases).
b. Cation and anion
Answer:
| Cations | Anions |
|---|---|
| (i) Cations are ions with a net positive charge. | Anions are ions with a net negative charge. |
| (ii) Cations are generally formed by metals. When metals donate electrons, they have excess of protons, hence they form cations. | Anions are generally formed by non-metals. When non-metals accept electrons, they have excess of electrons, hence they form anions. |
| (iii) Cations are attracted towards the cathode which are negatively charged electrodes. | Anions are attracted towards the anode which are positively charged electrodes. |
| (iv) e.g.: Na+, Ca2+, Mg2+, K+ etc. | e.g.: O2-, S2-, Cl-, Br- etc. |
In simple words: Cations are positively charged ions formed when atoms lose electrons, usually metals, and are attracted to the negative electrode (cathode). Anions are negatively charged ions formed when atoms gain electrons, usually non-metals, and are attracted to the positive electrode (anode).
🎯 Exam Tip: Cations are positive and move towards the cathode (negative electrode); anions are negative and move towards the anode (positive electrode). This movement is fundamental to electrochemistry.
c. the Negative electrode and the positive electrode.
Answer:
| Negative Electrode | Positive Electrode |
|---|---|
| (i) Negatively charged electrodes are called as a cathode. | Positively charged electrodes are called as Anode. |
| (ii) Positively charged cations move towards the cathode or negative electrode. | Negatively charged anions move towards the anode or positive electrode. |
| (iii) Cathode accepts electrons from cations | Anode gives electrons to anions |
In simple words: The negative electrode is the cathode, attracting positively charged cations and providing electrons. The positive electrode is the anode, attracting negatively charged anions and accepting electrons from them.
🎯 Exam Tip: In an electrolytic cell, remember "Anode is Positive, Cathode is Negative" (APCN). Cations move to the cathode for reduction, and anions move to the anode for oxidation.
Question 12. Classify aqueous solutions of the following substances according to their pH into three groups : 7, more than 7, less than 7. Common salt, sodium acetate, hydrochloric acid, carbon dioxide, potassium bromide, calcium hydroxide, ammonium chloride, vinegar, sodium carbonate, ammonia, sulphur dioxide.
Answer:
| pH = 7 | pH > 7 | pH < 7 |
|---|---|---|
| (a) common salt. | sodium acetate. | sulphur dioxide. |
| (b) potassium bromide. | sodium carbonate | hydrochloric acid. |
| (c) | ammonia. | carbon-dioxide. |
| (d) | calcium hydroxide. | ammonium chloride. |
| (e) | vinegar |
In simple words: Solutions with pH=7 are neutral (common salt, potassium bromide). Those with pH>7 are basic (sodium acetate, sodium carbonate, ammonia, calcium hydroxide). Solutions with pH<7 are acidic (hydrochloric acid, carbon dioxide, sulphur dioxide, ammonium chloride, vinegar).
🎯 Exam Tip: pH 7 is neutral. pH less than 7 indicates acidity, with lower values meaning stronger acids. pH greater than 7 indicates alkalinity, with higher values meaning stronger bases. Knowledge of the parent acid/base helps predict a salt's pH.
Class 9 Science Chapter 5 Acids, Bases And Salts Intext Questions and Answers
Question 1. How are the following substances classified into three groups with the help of litmus? Lemon, tamarind, baking soda, buttermilk, vinegar, orange, milk, lime, tomato, milk of magnesia, water, alum.
Answer:
| Basic Substance: Turns Red Litmus Blue | Acidic Substance: Turns Blue Litmus Red | Neutral Substance: No change in the colour of litmus |
|---|---|---|
| Baking Soda | Lemon | water |
| Lime | Tamarind | |
| Milk of Magnesia | Buttermilk | |
| Vinegar | ||
| Orange | ||
| Milk | ||
| Tomato | ||
| Alum |
In simple words: Substances are classified by their reaction to litmus: those turning red litmus blue are basic (baking soda, lime, milk of magnesia), those turning blue litmus red are acidic (lemon, tamarind, buttermilk, vinegar, orange, milk, tomato, alum), and those causing no change are neutral (water).
🎯 Exam Tip: Litmus paper is a simple and effective indicator for quickly classifying substances as acidic or basic. Acidic substances contain H+ ions, while basic substances contain OH- ions, causing the characteristic color changes.
Question 2. Fill in the columns in the part of the following table:
Answer:
| Name of the compound | Molecular formula | Basic radical | Acidic radical | Type of the compound |
|---|---|---|---|---|
| Hydrochloric acid | HCl | H+ | Cl- | Acid |
| Nitric Acid | HNO3 | H+ | NO3- | Acid |
| Hydrogen Bromide | HBr | H+ | Br- | Acid |
| Sulphuric acid | H2SO4 | H+ | SO42- | Acid |
| Boric acid | H3BO3 | H+ | BO33- | Acid |
| Sodium hydroxide | NaOH | Na+ | OH- | Base |
| Potassium hydroxide | KOH | K+ | OH- | Base |
| Calcium hydroxide | Ca(OH)2 | Ca2+ | OH- | Base |
| Ammonium hydroxide | NH4OH | NH4+ | OH- | Base |
| Sodium chloride | NaCl | Na+ | Cl- | Salt |
| Calcium nitrate | Ca(NO3)2 | Ca2+ | NO3- | Salt |
| Potassium sulphate | K2SO4 | K+ | SO42- | Salt |
| Calcium chloride | CaCl2 | Ca2+ | Cl- | Salt |
| Ammonium sulphate | (NH4)2SO4 | NH4+ | SO42- | Salt |
In simple words: This table categorizes compounds by their molecular formula, identifies their basic (cation) and acidic (anion) radicals, and classifies them as either an acid, base, or salt. Acids provide H+, bases provide OH-, and salts are formed from both.
🎯 Exam Tip: To complete such tables, identify the cation (basic radical) and anion (acidic radical) from the chemical formula. If H+ is the only basic radical, it's an acid; if OH- is the only acidic radical, it's a base; otherwise, it's a salt.
Class 9 Science Chapter 5 Acids, Bases And Salts Intext Questions And Answers
Question 1. How are the following substances classified into three groups with the help of litmus? Lemon, tamarind, baking soda, buttermilk, vinegar, orange, milk, lime, tomato, milk of magnesia, water, alum.
Answer:
| Basic Substance: Turns Red Litmus Blue | Acidic Substance: Turns Blue Litmus Red | Neutral Substance: No change in the colour of litmus |
|---|---|---|
| Baking Soda | Lemon | water |
| Lime | Tamarind | |
| Milk of Magnesia | Buttermilk | |
| Vinegar | ||
| Orange | ||
| Milk | ||
| Tomato | ||
| Alum |
In simple words: Litmus paper helps identify whether a substance is acidic, basic, or neutral by changing color. Acids turn blue litmus red, bases turn red litmus blue, and neutral substances cause no color change.
🎯 Exam Tip: Remember common examples for each category (acidic, basic, neutral) to quickly classify substances based on their litmus test results. This is a fundamental concept for understanding pH.
Question 2. Fill in the columns in the part of the following table:
Answer:
| Name of the compound | Molecular formula | Basic radical | Acidic radical | Type of the compound |
|---|---|---|---|---|
| Hydrochloric acid | HCl | H\(^+\) | Cl\(^-\) | Acid |
| Nitric Acid | HNO\(_{\text{3}}\) | H\(^+\) | NO\(_{\text{3}}\)\( ^-\) | Acid |
| Hydrogen Bromide | HBr | H\(^+\) | Br\(^-\) | Acid |
| Sulphuric acid | H\(_{\text{2}}\)SO\(_{\text{4}}\) | H\(^+\) | SO\(_{\text{4}}\)\(^{2-}\) | Acid |
| Boric acid | H\(_{\text{3}}\)BO\(_{\text{3}}\) | H\(^+\) | BO\(_{\text{3}}\)\(^{3-}\) | Acid |
| Sodium hydroxide | NaOH | Na\(^+\) | OH\(^-\) | Base |
| Potassium hydroxide | KOH | K\(^+\) | OH\(^-\) | Base |
| Calcium hydroxide | Ca(OH)\(_{\text{2}}\) | Ca\(^{2+}\) | OH\(^-\) | Base |
| Ammonium hydroxide | NH\(_{\text{4}}\)OH | NH\(_{\text{4}}\)\(^+\) | OH\(^-\) | Base |
| Sodium chloride | NaCl | Na\(^+\) | Cl\(^-\) | Salt |
| Calcium nitrate | Ca(NO\(_{\text{3}}\))\(_2\) | Ca\(^{2+}\) | NO\(_{\text{3}}\)\( ^-\) | Salt |
| Potassium sulphate | K\(_{\text{2}}\)SO\(_{\text{4}}\) | K\(^+\) | SO\(_{\text{4}}\)\(^{2-}\) | Salt |
| Calcium chloride | CaCl\(_{\text{2}}\) | Ca\(^{2+}\) | Cl\(^-\) | Salt |
| Ammonium sulphate | (NH\(_{\text{4}}\))\(_2\)SO\(_{\text{4}}\) | NH\(_{\text{4}}\)\(^+\) | SO\(_{\text{4}}\)\(^{2-}\) | Salt |
In simple words: This table categorizes common chemical compounds by their molecular formula, basic radical (positive ion), acidic radical (negative ion), and overall type (acid, base, or salt), helping to understand their composition.
🎯 Exam Tip: Practice identifying the basic and acidic radicals in various compounds. This skill is crucial for predicting chemical reactions and understanding compound classifications.
Question 3. Complete the following table of the concentration of various aqueous solutions.
Answer:
| Solute | Quantity of solute | Volume of Solution | Concentration of the solution | ||||
|---|---|---|---|---|---|---|---|
| Name | Molecular formula | Molecular mass (u) | Gram (g) | Mole (mol) | Litre (l) | Gram/ Litre (g/l) | Molarity (M) mole/litre (mol/l) |
| Sodium chloride | NaCl | 58.5 u | 117 g | 2 mol | 2 l | 58.5 g/l | 1 M |
| Hydrogen chloride | HCl | 36.5 u | 3.65 g | 0.1 mol | 1 l | 3.65 g/l | 0.1 M |
| Sodium hydroxide | NaOH | 40 u | 60 g | 1.5 mol | 2 l | 30 g/l | 0.75 M |
In simple words: This table provides a quick reference for calculating and understanding solution concentration, showing how to convert between grams, moles, liters, and molarity for different solutes.
🎯 Exam Tip: Always remember the definitions of gram/litre and molarity. Practice converting between grams and moles, and volume to litres for different solutions to ace concentration calculations.
Question 4. Complete the following table of neutralization reactions and also write down the names of the acids, bases and salts in it.
Answer:
| Acid | + | Base | Salt | + | Water | |
|---|---|---|---|---|---|---|
| HNO\(_{\text{3}}\) | + | KOH | \( \implies \) | KNO\(_{\text{3}}\) | + | H\(_{\text{2}}\)O |
| Nitric acid | + | Potassium hydroxide | Potassium nitrate | + | water | |
| H\(_{\text{2}}\)SO\(_{\text{4}}\) | + | 2NH\(_{\text{4}}\)OH | \( \implies \) | (NH\(_{\text{4}}\))\(_2\)SO\(_{\text{4}}\) | + | 2H\(_{\text{2}}\)O |
| Sulphuric acid | + | Ammonium hydroxide | Ammonium sulphate | + | water | |
| HBr | + | KOH | \( \implies \) | KBr | + | H\(_{\text{2}}\)O |
| Hydrogen Bromide | + | Potassium hydroxide | Potassium Bromide | + | water |
In simple words: This table illustrates common neutralization reactions where an acid and a base combine to form a salt and water, showing balanced chemical equations and the names of reactants and products.
🎯 Exam Tip: Understanding the general formula "Acid + Base \(\implies\) Salt + Water" is key. Practice balancing chemical equations for various neutralization reactions to ensure full marks.
Question 5. What are the names of the following compounds? NH3, Na2O, CaO.
Answer:
NH3: Ammonia
Na2O: Sodium oxide
CaO: Calcium oxide
In simple words: This question asks for the common names of three basic chemical compounds: Ammonia (NH3), Sodium oxide (Na2O), and Calcium oxide (CaO).
🎯 Exam Tip: It is crucial to memorize the chemical formulas and common names of frequently encountered compounds to correctly identify them in various contexts.
Question 6. Into which type will you classify the above compounds, acid, base or salt?
Answer:
NH3: base
Na2O : base
CaO : base
In simple words: All three compounds - Ammonia (NH3), Sodium oxide (Na2O), and Calcium oxide (CaO) - are classified as bases because they can accept protons or donate hydroxide ions in solution.
🎯 Exam Tip: Understand the definitions of acids, bases, and salts. Recall that many metal oxides are basic, and ammonia is a common weak base.
Question 7. Give examples of monobasic, dibasic and tribasic acids.
Answer:
Monobasic acid examples: HNO3, HCl, CH3COOH
Dibasic acid examples: H2SO4, H2CO3
Tribasic acid examples: H3BO3, H3PO4
In simple words: Monobasic acids release one hydrogen ion, dibasic acids release two, and tribasic acids release three when dissolved in water.
🎯 Exam Tip: Pay attention to the number of replaceable hydrogen atoms in the acid's formula to determine its basicity. Stronger acids are often, but not always, polybasic.
Question 8. Give the three types of bases with their examples.
Answer:
Types of bases:
Monoacidic base examples : NaOH, KOH, NH4OH
Diacidic base examples: Ca(OH)2, Ba(OH)2
Triacidic base examples: Al(OH)3, Fe(OH)3
In simple words: Bases are categorized by how many hydroxide ions they can release: monoacidic bases release one, diacidic bases release two, and triacidic bases release three.
🎯 Exam Tip: Similar to acids, the 'acidity' of a base refers to the number of hydroxide ions it can furnish. Learn typical examples for each type to quickly classify them.
Question 9. What are the colours of the following natural and synthetic indicators in acidic and basic solutions? Litmus, turmeric, jamun, methyl orange, phenolphthalein?
Answer:
| Indicator | Colour in Acidic Solution | Colour in basic Solution |
|---|---|---|
| Litmus | Red | Blue |
| Turmeric | Yellow | Red |
| Jamun | Red | Blue-Green |
| Methyl orange | Red | Yellow |
| Phenolphthalein | Colourless | Pink |
In simple words: Indicators are substances that change color in the presence of an acid or a base, providing a visual cue about the solution's pH.
🎯 Exam Tip: It is crucial to remember the color changes for common indicators in both acidic and basic mediums, as these are frequently tested in practical and theoretical exams.
Question 10. On mixing the substances as shown here, what are the resulting mixtures formed
(a) Water and salt
(b) Water and sugar
(c) Water and sand
(d) Water and sawdust
Answer:
(a) Water and salt - Homogeneous mixture
(b) Water and sugar - Homogeneous mixture
(c) Water and sand - Heterogeneous mixture
(d) Water and sawdust - Heterogeneous mixture
In simple words: When substances are mixed, they form either homogeneous mixtures (where components are evenly distributed, like salt in water) or heterogeneous mixtures (where components remain separate, like sand in water).
🎯 Exam Tip: Differentiate between homogeneous and heterogeneous mixtures based on whether the components are uniformly distributed throughout the mixture. Solubility is a key factor here.
Question 11. What would be the definition of an acid and a base with reference to the neutralization reaction?
Answer:
- Acid: An acid is a substance which neutralises a base to form salt and water.
- Base: A base is a substance which neutralises an acid to form salt and water.
In simple words: In a neutralization reaction, an acid is what reacts with a base to create salt and water, and a base is what reacts with an acid to do the same.
🎯 Exam Tip: Focus on the outcome of the reaction – the formation of salt and water – to define acids and bases in the context of neutralization. This highlights their complementary roles.
Answer The Following Questions:
Question 1. Take aqueous solution of sodium chloride, copper sulphate, glucose, urea, dil.H2SO4 and dil.NaOH in a beaker and test the electrical conductivity of the solutions. Answer the given below questions.
(a) With which solutions did the bulb glow?
Answer: Solutions with which bulb glows: Aqueous solution of NaCl, CuSO4, H2SO4 and NaOH.
(b) Which solutions are electrical conductors?
Answer: Solutions which are electrical conductors: NaCl, CuSO4, H2SO4 and NaOH.
In simple words: The bulb glows and solutions conduct electricity when they contain ions, which are present in salts (NaCl, CuSO4), strong acids (H2SO4), and strong bases (NaOH), but not in non-electrolytes like glucose and urea.
🎯 Exam Tip: Remember that conductivity in solutions depends on the presence of mobile ions. Ionic compounds, strong acids, and strong bases dissociate into ions and thus conduct electricity well.
Question 2. During electrolysis of copper sulphate, if electric current is passed through the electrolytic cell for a long time, what change would be seen at the anode?
Answer:
- When electricity is passed for a long time through copper sulphate solution, the following reaction is seen at the anode: Anode Reaction: \( \text{Cu}_{\text{(s)}} \implies \text{Cu}^{2+}_{\text{(aq)}} + \text{2e}^- \)
- All the copper atoms will get converted into copper ions and get deposited on the cathode. This process continues till the copper anode exists.
In simple words: During electrolysis of copper sulphate, the copper anode will gradually dissolve, converting solid copper into copper ions which then move to the cathode.
🎯 Exam Tip: In electrolysis, understand that oxidation occurs at the anode. For a reactive anode like copper, the anode itself can oxidize and dissolve, affecting the solution and electrode mass.
Question 3. Would water be a good conductor of electricity?
Answer: Pure water is not a good conductor of electricity.
In simple words: Pure water is a poor conductor of electricity because it has very few free ions to carry the electric current.
🎯 Exam Tip: Distinguish between pure water (poor conductor) and water with dissolved salts or acids/bases (good conductor). The presence of ions is critical for electrical conductivity.
Answer The Following Questions:
Question 1. (i) With which solutions did the bulb glow?
(ii) Which solutions are electrical conductors?
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक साधारण परिपथ दिखाता है जिसका उपयोग किसी विलयन की विद्युत चालकता का परीक्षण करने के लिए किया जाता है। इसमें एक बैटरी, एक स्विच, एक बल्ब और दो इलेक्ट्रोड एक बीकर में सोडियम क्लोराइड के विलयन में डूबे हुए हैं। इलेक्ट्रोड नंगे बिजली के तारों से बने हैं, जो यह दर्शाता है कि इलेक्ट्रोलाइटिक सेल कैसे काम करता है।
Answer:
(i) The bulbs glows when the wire are immersed in NaCl solution.
(ii)
| Solution | Results |
|---|---|
| 1g Copper Sulphate Solution | Bulb glow |
| 1g Glucose Solution | Bulb does not glow |
| 1g Urea Solution | Bulb does not glow |
| 5ml dil.H2SO4 Solution | Bulb glows |
| 5ml dil. NaOH Solution | Bulb glows |
In simple words: The experiment shows that solutions of ionic compounds (like salt, copper sulphate) and strong acids/bases (like H2SO4, NaOH) conduct electricity, making the bulb glow, while solutions of molecular compounds (like glucose, urea) do not.
🎯 Exam Tip: This experiment demonstrates that for a solution to conduct electricity, it must contain free-moving ions. Electrolytes produce ions in solution, while non-electrolytes do not.
Question 2. What would be the definition of an acid and a base with reference to the neutralization reaction?
Answer:
- Acid: An acid is a substance which neutralises a base to form salt and water.
- Base: A base is a substance which neutralises an acid to form salt and water.
In simple words: In a neutralization reaction, an acid is defined as the substance that reacts with a base to produce salt and water, while a base is the substance that reacts with an acid to do the same.
🎯 Exam Tip: This definition emphasizes the reactive nature of acids and bases in the context of their ability to cancel out each other's properties, resulting in neutral products.
Question 3. Dissolve 2g salt in 500ml pure water. Take 250 ml of this solution in a 500ml capacity beaker. Connect two electrical wires to the positive and negative terminals of a power supply. Remove the insulating cladding from about 2cm portions at the other ends of the wires. These are the two electrodes. Fill two test tubes upto the brim with the prepared dilute salt solution. Invert them on the electrodes without allowing any air to enter. Start the electric current under 6V potential difference from the power supply. Observe what happens in the test tubes after some time.
(a) Did you see the gas bubbles forming near the electrodes in the test tubes?
Answer: Yes, gas bubbles can be seen forming near the electrodes in the test tube.
(b) Are these gases heavier or lighter than water?
Answer: These gases are lighter than water.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र पानी के इलेक्ट्रोलिसिस का एक सेटअप दिखाता है। इसमें दो टेस्ट ट्यूब हैं जिन्हें एक बीकर में पानी से भरे इलेक्ट्रोड पर उल्टा रखा गया है। इलेक्ट्रोड एक बैटरी से जुड़े हैं, और जब विद्युत प्रवाह पास होता है, तो गैसें टेस्ट ट्यूब में जमा होती हैं, जो पानी के घटकों में विघटन को दर्शाती हैं।
(c) Are the volumes of the gases collected over the solution in the two test tubes the same or different?
Answer: The volumes of gases collected over the solution in the two test tubes are different.
(d) Test the solutions in the two test tubes with litmus paper, what do you see?
Answer: The solution in the cathode turns red litmus blue while solution in anode turns blue litmus red.
(e) When the above experiment is repeated with dil H2SO4 and dil NaOH, Hydrogen gas is liberated at cathodes and oxygen gas is liberated at anode.
In simple words: This experiment demonstrates the electrolysis of a salt solution (or dilute acid/base), where electric current breaks down water, producing hydrogen gas at the cathode and oxygen gas at the anode, with different volumes and pH changes at each electrode.
🎯 Exam Tip: This activity highlights key principles of electrolysis: gas evolution at electrodes, volume ratios of gases produced (especially for water), and pH changes, all of which are important for understanding electrochemical reactions.
Question 1. Cut a lemon into two equal parts. Take the juice of each part into two separate beakers. Pour 10 ml of drinking water in one beaker and 20 ml in the second. Stir the solutions in both the beakers and taste them. Is there any difference in the tastes of the solutions in the two beakers? What is that difference?
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र दो बीकरों में नींबू के रस के विलयन को दर्शाता है। बीकर 'ए' में 10 मिली पानी मिलाया गया है, जबकि बीकर 'बी' में 20 मिली पानी मिलाया गया है, जो विभिन्न सांद्रता वाले दो नींबू के रस के विलयन को प्रदर्शित करता है।
Answer:
- In the above activity, the sour taste of the solutions is because of the solute, lemon juice in them.
- The quantity of the lemon juice is the same in both the solutions. Yet their tastes are different.
- The solution in the first beaker is more sour than the one in the second.
- Although the quantity of the solute is the same in both the solutions, the quantity of the solvent is different.
- Ratio of the quantity of the solute to the quantity of the resulting solution is different. This ratio is larger for the solution in the first beaker and therefore that solution tastes more sour.
- On the other hand, the proportion of the lemon juice in the total solution in the second beaker is smaller and taste is less sour.
- The taste of foodstuff depends upon the nature of the taste-giving ingredient and its proportions in the foodstuff.
- Similarly, all the properties of a solution depend on the nature of the solute and solvent and also on the proportion of the solute in a solution
- The proportions of a solute in a solution is called the concentration of the solute in the solution.
In simple words: When the same amount of lemon juice is diluted with different amounts of water, the solution with less water tastes more sour because its concentration of lemon juice is higher.
🎯 Exam Tip: This experiment beautifully demonstrates the concept of concentration and how it affects properties like taste. Understanding that concentration is the ratio of solute to solvent is vital.
Question 2. Take a big test tube. Choose a rubber stopper in which a gas tube can be fitted. Take a few pieces of magnesium ribbon in the test tube and add some dilute HCl to it. Take a lighted candle near the end of the gas tube and observe. What did you observe?
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक टेस्ट ट्यूब में एक धातु के साथ एक तनु मजबूत अम्ल की प्रतिक्रिया को दर्शाता है। टेस्ट ट्यूब में मैग्नीशियम रिबन और तनु HCl है, और बुलबुले (हाइड्रोजन गैस) बन रहे हैं। एक रबर कॉर्क और गैस ट्यूब के माध्यम से, यह हाइड्रोजन गैस के जलने का वर्णन करता है, जो धातु-अम्ल प्रतिक्रिया का एक सामान्य परीक्षण है।
Answer:
- Magnesium metal reacts with dilute HCl and an inflammable gas, hydrogen, is formed.
- During this reaction, the reactive metal displaces hydrogen from the acid to release hydrogen gas.
- At the same time, the metal is converted into basic radical which combines with the acidic radical from the acid to form the salt.
\( \text{Mg}_{\text{(s)}} + \text{2HCl}_{\text{(aq)}} \implies \text{MgCl}_{\text{2(aq)}} + \text{H}_{\text{2(g)}} \)
In simple words: When magnesium metal reacts with dilute hydrochloric acid, it produces hydrogen gas, which can be identified by a "pop" sound when a lighted candle is brought near it.
🎯 Exam Tip: This is a classic test for hydrogen gas. Always remember that active metals react with acids to produce hydrogen gas and a salt. Write balanced equations for such reactions.
Question 3. Take some water in a test tube and add a little red oxide (the primer used before painting iron articles) to it. Now add a small quantity of dilute HCl to it, shake the test tube and observe.
(a) Does the red oxide dissolve in water?
Answer: The chemical formula of red oxide is Fe2O3. It is insoluble in water.
(b) What change takes place in the particles of red oxide on adding dilute HCl?
Answer: The water-insoluble red oxide reacts with HCl to produce a water-soluble salt FeCl3.
- This gives a yellowish colour to the water.
- The following chemical equation can be written for this chemical change.
\( \text{Fe}_{\text{2}}\text{O}_{\text{3(s)}} + \text{6HCl}_{\text{(aq)}} \implies \text{2FeCl}_{\text{3(aq)}} + \text{3H}_{\text{2}}\text{O}_{\text{(l)}} \)
In simple words: Red oxide (iron(III) oxide) doesn't dissolve in water but reacts with dilute hydrochloric acid to form a water-soluble iron chloride salt, changing the solution to a yellowish color.
🎯 Exam Tip: Remember that many metal oxides, though insoluble in water, can react with acids (showing basic character) to form a salt and water. This is a common characteristic of basic oxides.
Question 4. Fit a bent tube in a rubber cork. Take some lime water in a test tube and keep it handy. Take some baking soda in another test tube and add some lemon juice to it. Immediately fit the bent tube over it. Insert its other end into the lime water. Note down your observations of both the test tubes. Repeat the procedure using washing soda, vinegar and dilute HC1 properly. What do you see?
Answer:
- In this activity, when limewater comes in contact with the gas released in the form of an effervescence, it turns milky.
- This is a chemical test for carbon dioxide gas.
- When lime water turns milky, we infer that the effervescence is of CO2.
- This gas is produced on the reaction of acids with carbonate and bicarbonate salts of metals.
- A precipitate of CaCO3 is produced on its reaction with the lime water Ca(OH)2.
- This reaction can be represented by the following chemical equation.
\( \text{Ca(OH)}_{\text{2(aq)}} + \text{CO}_{\text{2(g)}} \implies \text{CaCO}_{\text{3(s)}} + \text{H}_{\text{2}}\text{O}_{\text{(l)}} \)
- Washing soda is sodium carbonate Na2CO3. It will react same as baking soda (NaHCO3).
- Vinegar and HCl are acids, they do not react chemically with lemon juice.
In simple words: Adding acids to carbonates like baking soda or washing soda releases carbon dioxide gas, which turns limewater milky, confirming its presence.
🎯 Exam Tip: The limewater test is the classic method to identify carbon dioxide. Remember that carbonates and bicarbonates react with acids to produce CO2, water, and a salt.
Class 9 Science Chapter 5 Acids, Bases And Salts Additional Important Questions And Answers
Select The Correct Option
Question 1. - acid is present in lemon.
(a) malic acid
(b) tartaric acid
(c) citric acid
(d) butyric acid
Answer: (c) Citric acid
In simple words: Lemon contains citric acid, which is responsible for its characteristic sour taste.
🎯 Exam Tip: Know the common acids found in various natural products; this is a frequent general knowledge or MCQ question in exams.
Question 2. Tamarind contains - acid.
(a) Lactic acid
(b) tartaric acid
(c) matlic acid
(d) butyric acid
Answer: (b) tartaric acid
In simple words: Tamarind contains tartaric acid, which gives it its distinctive sour flavor.
🎯 Exam Tip: Familiarize yourself with the organic acids present in different fruits and food items; this helps in understanding their chemical composition and properties.
Question 3. Buttermilk contains - acid.
(a) butyric acid
(b) Lactic acid
(c) matlic acid
(d) citric acid
Answer: (a) Butyricacid
In simple words: Buttermilk primarily contains lactic acid, formed from the fermentation of lactose by bacteria.
🎯 Exam Tip: Relate common food items to the specific acids they contain. Understanding fermentation processes can help recall such facts.
Question 4. If the basic radical is H+ the type of compound is -
(a) neutral
(b) base
(c) acid
(d) alkali
Answer: (c) Acid
In simple words: A compound whose basic radical is H+ is classified as an acid, as acids release hydrogen ions in solution.
🎯 Exam Tip: Remember that acids are defined by their ability to produce H+ ions (the basic radical in this context) when dissolved in water.
Question 5. The name of compound NH3 is -
(a) nitric acid
(b) ammonium
(c) nitride
(d) ammonia
Answer: (d) ammonia
In simple words: NH3 is the chemical formula for ammonia, a common base.
🎯 Exam Tip: It is essential to correctly associate chemical formulas with their common names, especially for frequently encountered compounds like ammonia.
Question 6. The bases which are soluble in water are called as -
(a) indicators
(b) acids
(c) alkalis
(d) salts
Answer: (c) alkalis
In simple words: Bases that dissolve in water are specifically known as alkalis.
🎯 Exam Tip: Understand the distinction: all alkalis are bases, but not all bases are alkalis. Alkalinity refers to water solubility.
Question 7. H3PO4 is a - acid.
(a) monobasic
(b) tribasic
(c) tetrabasic
(d) dibasic
Answer: (b) tribasic
In simple words: H3PO4, or phosphoric acid, is a tribasic acid because it can donate three hydrogen ions per molecule.
🎯 Exam Tip: The basicity of an acid is determined by the number of replaceable hydrogen atoms it contains. For H3PO4, there are three such hydrogen atoms.
Question 8. According to pH scale pure water has a pH of -
(a) 6
(b) 7
(c) 5
(d) 8
Answer: (b) 7
In simple words: Pure water is neutral, and on the pH scale, a neutral solution has a pH value of 7.
🎯 Exam Tip: Remember the pH scale ranges from 0-14, with 7 being neutral, below 7 acidic, and above 7 basic. Pure water is the classic example of a neutral substance.
Question 9. With reference to neutralization, metallic oxides are - in nature.
(a) basic
(b) neutral
(c) acidic
(d) saline
Answer: (a) basic
In simple words: Metallic oxides are typically basic in nature, meaning they react with acids in neutralization reactions to form salt and water.
🎯 Exam Tip: This is a fundamental concept: most metal oxides are basic, while most non-metal oxides are acidic. This understanding helps predict reaction outcomes.
Question 10. Molecular formula of blue vitriol is -
(a) CuSO3 5H2O
(b) CuSO4 4H2O
(c) CUSO3 4H2O
(d) CUSO4 5H2O
Answer: (d) CUSO4 5H2O
In simple words: Blue vitriol is the common name for hydrated copper(II) sulfate, which has the molecular formula CuSO4·5H2O.
🎯 Exam Tip: It's important to know the molecular formulas and common names for hydrated salts, as the water of crystallization is a significant part of their structure and properties.
Question 11. Molecular formula of crystalline alum is -
(a) KSO4, AISO4, 24H2O
(b) K2SO4, ALSO4, 24H2O
(c) K2SO4, AL2(SO4)3, 24H2O
(d) KSO4, Al2(SO4)3, 24H2O
Answer: (c) K2SO4, AL2(SO4)3, 24H2O
In simple words: Crystalline alum, specifically potassium alum, has the complex molecular formula K2SO4·Al2(SO4)3·24H2O, indicating it's a double salt with extensive hydration.
🎯 Exam Tip: Alums are double salts with a specific general formula. Memorizing the full formula, including the water of crystallization, is necessary for this type of question.
Question 12. Molecular formula for sodium oxide is -
(a) Na2O
(b) NaO2
(c) NaO
(d) Na2O2
Answer: (a) Na2O
In simple words: Sodium oxide is an ionic compound formed between sodium and oxygen, with the chemical formula Na2O.
🎯 Exam Tip: Ensure you understand how to write chemical formulas based on the valencies of the constituent elements. Sodium has a valency of +1, and oxygen typically -2.
Question 13. H2CO3 is - acid.
(a) monobasic
(b) dibasic
(c) tribasic
(d) tetrabasic
Answer: (b) dibasic
In simple words: Carbonic acid (H2CO3) is a dibasic acid because it can release two hydrogen ions when it dissociates.
🎯 Exam Tip: To determine the basicity of an acid, count the number of hydrogen atoms that can be replaced by a metal or basic radical in a reaction.
Question 14. Molecular formula of Red oxide is ............
(a) Fe2O3
(b) CuO
(c) Fe3O4
(d) Na2O
Answer: (a) Fe2O3
In simple words: The chemical formula for red oxide, commonly known as rust, is Fe2O3.
🎯 Exam Tip: Knowing the chemical formulas of common oxides is crucial for multiple-choice questions.
Question 15. The positive terminal electrode is called as ............
(a) anode
(b) cathode
(c) anion
(d) cation
Answer: (a) anode
In simple words: The anode is the positive electrode in an electrolytic cell, attracting negatively charged ions.
🎯 Exam Tip: Remember that "anode" and "positive" start with a vowel sound (A-node, A-node) and "cathode" and "negative" start with a consonant (C-athode, N-egative) to easily recall their charges.
Question 16. ............ produced in stomach helps in digestion.
(a) Hydrochloric acid
(b) Oxalic acid
(c) Sulphuric acid
(d) Nitric acid?
Answer: (a) Hydrochloric acid
In simple words: Hydrochloric acid (HCl) is naturally produced in the stomach and plays a vital role in breaking down food and killing harmful bacteria during digestion.
🎯 Exam Tip: Connect common acids to their everyday biological functions, like HCl in stomach digestion.
Question 17. The solution turns blue litmus red, its pH is likely to be ............
(a) 7
(b) 4
(d) 9
Answer: (b) 4
In simple words: A solution that turns blue litmus red is acidic, and acidic solutions have a pH less than 7, so 4 is the most likely pH.
🎯 Exam Tip: The litmus test is a fundamental indicator for acidity (red for acid) and basicity (blue for base), with pH less than 7 for acids and greater than 7 for bases.
Question 18. An ionic compound NaCl is formed by ............
(a) Na+ and Cl-
(b) Na+ and Cl+
(c) Na- and Cl-
(d) Na- and Cl+
Answer: (a) Na+ and Cl-
In simple words: Sodium chloride (NaCl) is an ionic compound formed by the electrostatic attraction between a positively charged sodium ion (Na+) and a negatively charged chloride ion (Cl-).
🎯 Exam Tip: Remember that ionic compounds are formed between a metal (which forms a cation, positive ion) and a non-metal (which forms an anion, negative ion).
Question 19. pH of strong acid is ............
(a) 0
(b) 7
(c) 8
(d) 14
Answer: (a) 0
In simple words: Strong acids have very low pH values, with pH 0 indicating extreme acidity, lower than 7.
🎯 Exam Tip: A pH of 7 is neutral, values below 7 indicate acidity (stronger as pH approaches 0), and values above 7 indicate basicity (stronger as pH approaches 14).
Question 20. HCl + NaOH → NaCl + H2O is a ............ reaction.
(a) neutralization
(b) crystallisation
(c) electrolysis
(d) dissociation
Answer: (a) neutralization
In simple words: This reaction shows an acid (HCl) reacting with a base (NaOH) to form a salt (NaCl) and water (H2O), which is the definition of a neutralization reaction.
🎯 Exam Tip: Recognizing the products (salt and water) from an acid-base reaction is key to identifying neutralization.
Question 21. Adding water to acid is an ............ reaction.
(a) endothermic
(b) exothermic
(c) neutralisation
(d) crystallisation
Answer: (b) exothermic
In simple words: The process of adding water to acid releases a significant amount of heat, making it an exothermic reaction.
🎯 Exam Tip: Always add acid to water slowly and with stirring, never water to acid, to manage the heat released in this exothermic dilution.
Find the odd one out:
Answer:
(a) Phenolphthalein is odd one out as rest are natural indicators while phenolphthalein is a synthetic indicator.
(b) Lime water is odd one out as this is basic in nature while rest are acidic.
(c) NaHCO3 is odd one out as it is base while rest are acids.
(d) Nitric acid is odd one out as others are weak acids while Nitric acid is a strong acid.
(e) Crystalline is odd one out as this is nature of a compound while others are physical states of compounds.
(f) NaOH is odd one out even though all are bases but NaOH is highly soluble in water compared to others.
In simple words: In "Find the odd one out" questions, the key is to identify the common characteristic among a group of items and then pinpoint the one that doesn't share that trait, often due to a different chemical nature, physical state, or classification.
🎯 Exam Tip: For "odd one out" questions, classify each item first (e.g., acid, base, indicator type, solubility) and then look for the one that deviates from the group's common category.
Question 1. Name the three types of ionic compounds.
Answer: The three types of ionic compounds are acids, bases and salts.
In simple words: Ionic compounds can be broadly categorized into acids, bases, and salts, each with distinct chemical properties based on their dissociation in water.
🎯 Exam Tip: Understand that acids, bases, and salts are all ionic compounds because they dissociate into ions in solution.
Question 2. Name the two constituents of molecule of an ionic compound.
Answer:
- Cation (positive ion/ basic radical)
- Anion (negative ion/acidic radical).
In simple words: An ionic compound is always made up of a positively charged ion called a cation and a negatively charged ion called an anion.
🎯 Exam Tip: Identifying cations and anions is fundamental to understanding the composition and nomenclature of ionic compounds.
Question 3. Name any three acids with their molecular formula.
Answer:
- Hydrochloric acid – HCl
- Sulphuric acid – H2SO4
- Nitric acid – HNO3
In simple words: Hydrochloric acid, Sulphuric acid, and Nitric acid are common examples of strong acids used in various chemical processes.
🎯 Exam Tip: Memorize the common names and chemical formulas for key acids and bases as they frequently appear in exams.
Question 4. Name any three bases with their molecular formula.
Answer:
- Sodium hydroxide – NaOH
- Potassium hydroxide – KOH
- Calcium hydroxide – Ca(OH)2
In simple words: Sodium hydroxide, Potassium hydroxide, and Calcium hydroxide are common examples of bases, each having a distinct molecular formula.
🎯 Exam Tip: It's important to recognize that most bases contain a hydroxide group (OH) in their formula.
Question 5. Name any three salts with their molecular formula.
Answer:
- Sodium chloride – NaCl
- Potassium sulphate – K2SO4
- Calcium chloride – CaCl2
In simple words: Sodium chloride, Potassium sulphate, and Calcium chloride are examples of salts, typically formed from the reaction of an acid and a base.
🎯 Exam Tip: Salts are formed by the combination of a cation from a base and an anion from an acid.
Question 6. Name any two strong acids.
Answer:
- Hydrochloric acid – HCl
- Sulphuric acid – H2SO4
In simple words: Hydrochloric acid and Sulphuric acid are both examples of strong acids because they completely dissociate in water.
🎯 Exam Tip: Strong acids fully ionize in solution, releasing a high concentration of H+ ions, while weak acids only partially ionize.
Question 7. Name any two weak acids.
Answer:
- Acetic acid – CH3COOH
- Carbonic acid – H2CO3
In simple words: Acetic acid and Carbonic acid are examples of weak acids, meaning they only partially dissociate into ions when dissolved in water.
🎯 Exam Tip: Weak acids are characterized by incomplete dissociation in water, resulting in a lower concentration of H+ ions compared to strong acids.
Question 8. Name any two strong bases.
Answer:
- Sodium hydroxide – NaOH
- Potassium hydroxide – KOH
In simple words: Sodium hydroxide and Potassium hydroxide are strong bases because they completely dissociate in water, releasing a high concentration of OH- ions.
🎯 Exam Tip: Like strong acids, strong bases fully ionize in solution, leading to a high concentration of OH- ions, while weak bases only partially ionize.
Question 9. Name a weak base.
Answer: Ammonium hydroxide – NH4OH
In simple words: Ammonium hydroxide is a common example of a weak base because it only partially dissociates into ions in water.
🎯 Exam Tip: Understand that weak bases do not fully dissociate, maintaining a significant proportion of undissociated molecules in solution.
Question 10. Name any two alkalis.
Answer:
- Sodium hydroxide – NaOH
- Potassium hydroxide – KOH
In simple words: Sodium hydroxide and Potassium hydroxide are examples of alkalis, which are strong bases that are soluble in water.
🎯 Exam Tip: All alkalis are bases, but not all bases are alkalis; alkalis are specifically water-soluble bases.
Question 11. Name any two acids with their basicity 1 (monobasic)
Answer:
- Hydrochloric acid – HCl
- Nitric acid – HNO3
In simple words: Hydrochloric acid and Nitric acid are monobasic acids because each molecule produces only one hydrogen ion (H+) upon dissociation.
🎯 Exam Tip: Basicity refers to the number of replaceable hydrogen atoms in an acid; monobasic acids have one, dibasic two, and tribasic three.
Question 12. Name any two acids with their basicity 2 (dibasic)
Answer:
- Sulphuric acid – H2SO4
- Carbonic acid – H2CO3
In simple words: Sulphuric acid and Carbonic acid are dibasic acids because each molecule can donate two hydrogen ions (H+) when dissolved in water.
🎯 Exam Tip: The subscript for hydrogen in the chemical formula often indicates the basicity of an acid, but not always (e.g., CH3COOH has 4 hydrogens but is monobasic).
Question 13. Name any two acids with their basicity 3 (tribasic)
Answer:
- Boric acid – H3BO3
- Phosphoric acid – H3PO4
In simple words: Boric acid and Phosphoric acid are tribasic acids, meaning each molecule can release three hydrogen ions (H+) in solution.
🎯 Exam Tip: Understanding basicity helps predict the stoichiometry of acid-base reactions.
Question 14. Name any two bases with their acidity 1 (monoacidic)
Answer:
- Sodium hydroxide – NaOH
- Potassium hydroxide – KOH
In simple words: Sodium hydroxide and Potassium hydroxide are monoacidic bases because each molecule yields one hydroxide ion (OH-) upon dissociation in water.
🎯 Exam Tip: Acidity of a base refers to the number of hydroxyl ions (OH-) a molecule can produce; monoacidic bases have one, diacidic two, and triacidic three.
Question 15. Name any two bases with their acidity 2 (diacidic)
Answer:
- Calcium hydroxide – Ca(OH)2
- Barium hydroxide – Ba(OH)2
In simple words: Calcium hydroxide and Barium hydroxide are diacidic bases because each molecule can produce two hydroxide ions (OH-) in solution.
🎯 Exam Tip: The subscript for the hydroxide group in the chemical formula usually indicates the acidity of a base.
Question 16. Name any two bases with their acidity 3 (triacidic)
Answer:
- Aluminium hydroxide – Al(OH)3
- Ferric hydroxide – Fe(OH)3
In simple words: Aluminium hydroxide and Ferric hydroxide are triacidic bases, as each molecule can release three hydroxide ions (OH-) when dissolved.
🎯 Exam Tip: Higher acidity in bases indicates a greater capacity to neutralize acids due to more OH- ions.
Question 17. Name the two units to express the concentration of the solution.
Answer:
- mass of solute in grams dissolved in one litre of the solution grams per litre, (g/L).
- Number of moles of the solute dissolved in one litre of the solution. Molarity (M) of the solution.
In simple words: The concentration of a solution can be expressed as grams per litre (g/L) to show mass concentration, or as Molarity (M) to show molar concentration.
🎯 Exam Tip: Remember that g/L expresses mass concentration, while Molarity (mol/L) expresses molar concentration, both are crucial in quantitative chemistry.
Match the columns:
Question 1.
Column 'A'
(1) HNO3
(2) H3PO4
(3) CH3COOH
(4) H2CO3
Column 'B'
(a) Acetic acid
(b) Carbonic acid
(c) Phosphoric acid
(d) Nitric acid
Answer: (1-d), (2- c), (3 – a), (4 – b)
In simple words: This matching exercise correctly pairs chemical formulas of acids with their common names.
🎯 Exam Tip: Regularly review chemical formulas and their corresponding names to improve recall speed and accuracy.
Question 2.
Column 'A'
(1) NH4OH
(2) Ca(OH)2
(3) Al(OH)3
(4) Ba(OH)2
Column 'B'
(a) Aluminium Hydroxide
(b) Barium Hydroxide
(c) Calcium Hydroxide
(d) Ammonium Hydroxide
Answer: (1-d), (2- c), (3 – a), (4 – b)
In simple words: This correctly matches the chemical formulas of various bases with their respective names.
🎯 Exam Tip: Pay close attention to subscripts in formulas like Ca(OH)2 and Al(OH)3 to differentiate between similar-sounding hydroxides.
Question 3.
Column 'A' Solution
(1) Milk
(2) Milk of Magnesia
(3) 1 M HCl
(4) 1 M NaOH
Column 'B' pH
(a) 0
(b) 14
(c) 10.5
(d) 6.5
Answer: (1-d), (2- c), (3 – a), (4 – b)
In simple words: This matches common substances and solutions with their typical pH values, indicating their acidic, neutral, or basic nature.
🎯 Exam Tip: Understand the pH scale ranges: 0-6.9 for acids, 7 for neutral, and 7.1-14 for bases, with strong acids/bases at the extremes.
Question 4.
Column 'A'
(1) Urine
(2) Apples
(3) Orange
(4) Butter
Column'B'
(a) Butyric acid
(b) Uric acid
(c) Malic acid
(d) Citric acid
Answer: (1 – b), (2 – c), (3 – d), (4 – a)
In simple words: This exercise connects everyday items with the specific acids found within them.
🎯 Exam Tip: Familiarize yourself with common naturally occurring acids and their sources for a broader understanding of chemistry in daily life.
Question 5.
Column 'A'
(1) Crystalline blue vitriol
(2) Crystalline green vitriol
(3) Crystalline
(4) washing soda Crystalline alum
Column 'B'
(a) FeSO4-7H2O
(b) K2SO4-Al2(SO4)3.24H2O
(c) CuSO4-5H2O
(d) Na2CO310H2O
Answer: (1-c), (2- a), (3 – d), (4 – b)
In simple words: This section links the common names of crystalline compounds, including hydrated salts, with their correct molecular formulas.
🎯 Exam Tip: Memorize the formulas of common hydrated salts, paying attention to the number of water molecules of crystallization.
State whether the following statements are true or false and if false. Correct the false statement:
Answer:
(1) False. The separation of H⁺ and Cl¯ in HCl is in presence of water.
(2) True
(3) True
(4) True
(5) False. Turmeric is a natural indicator.
(6) False. Metal + Dilute acid forms salt and hydrogen gas.
(7) False. Iron oxide is called red primer.
(8) False. Oxide of izan-metal + Base → Salt + Water.
(9) True
(10) True
(11) False. Blue Vitriol is CuSO4. 5H2O.
(12) False. Molecular formula for crystalline Ferrous sulphate is FeSO4. 7H2O.
(13) False. NaCl in water conducts electricity.
(14) False, Phenolphthalein is colourless in acid and pink in base.
In simple words: These statements test knowledge of fundamental chemical concepts related to acids, bases, salts, indicators, and reactions.
🎯 Exam Tip: Carefully read each statement and recall the relevant chemical principles to determine truthfulness. For false statements, identify the specific incorrect detail.
Define the following:
Question 1. Acid
Answer: An acid is a substance which on dissolving in water gives rise to H ion as the only cation. For example, HCl, H2SO4, H2CO3.
\(HCl_{(g)} \xrightarrow{Water \ (dissociation)} H^{+}_{(aq)} + Cl^{-}_{(aq)}\)
\(H_2SO_{4(l)} \xrightarrow{Water \ (dissociation)} H^{+}_{(aq)} + HSO^{-}_{4 (aq)}\)
\(HSO^{-}_{4 (aq)} \xrightarrow{(dissociation)} H^{+}_{(aq)} + SO^{2-}_{4 (aq)}\)
In simple words: An acid is any substance that releases hydrogen ions (H+) when dissolved in water, acting as the sole positive ion.
🎯 Exam Tip: The Arrhenius definition of an acid focuses on the production of H+ ions in aqueous solution; remember to write the dissociation equations for full marks.
Question 2. Base
Answer: A base is a substance which on dissolving in water gives rise to the OW ion as the only anion. For, NaOH, Ca(OH)2
\(NaOH_{(s)} \xrightarrow{Water \ (dissociation)} Na^{+}_{(aq)} + OH^{-}_{(aq)}\)
\(Ca(OH)_{2 (s)} \xrightarrow{Water \ (dissociation)} Ca^{2+}_{(aq)} + 2OH^{-}_{(aq)}\)
In simple words: A base is a substance that produces hydroxide ions (OH-) as the only negative ion when dissolved in water.
🎯 Exam Tip: For bases, the Arrhenius definition emphasizes the release of OH- ions in water. Make sure to correctly balance the dissociation equations.
Question 3. Strong Acid
Answer: On dissolving in water, a strong acid dissociates almost completely, and the resulting aqueous solution contains mainly H ions and the concerned acidic radical. e.g. HCl, HBr, HNO3, H2SO4.
In simple words: A strong acid is an acid that completely breaks apart into hydrogen ions and its corresponding acidic radical when mixed with water.
🎯 Exam Tip: The key characteristic of a strong acid is its near-complete dissociation in water, leading to a very high concentration of H+ ions.
Question 4. Weak Acid
Answer: On dissolving in water a weak acid does not dissociate completely, and the resulting aqueous solution contains H+ ion and the concerned acidic radical in small proportion along with large proportion of the undissociated molecules of th acid, e.g., H2CO3 (Carbonic acid), CH3COOH (Acetic acid)
In simple words: A weak acid is an acid that only partially breaks down into hydrogen ions and its acidic radical when dissolved in water, leaving many molecules undissociated.
🎯 Exam Tip: Distinguish weak acids from strong acids by their incomplete dissociation, resulting in a lower concentration of H+ ions and higher proportion of intact acid molecules.
Question 5. Strong Base
Answer: On dissolving in water, a strong base dissociates almost completely and the resulting aqueous solution contains mainly OH ions and the concerned basic radicals, e.g. NaOH, KOH, Ca(OH)2, Na2O.
In simple words: A strong base is a base that almost entirely dissociates in water, yielding mostly hydroxide ions and its basic radical.
🎯 Exam Tip: Similar to strong acids, strong bases exhibit nearly complete dissociation in water, producing a high concentration of OH- ions.
Question 6. Weak Base
Answer: On dissolving in water, a weak base does not dissociate completely and the resulting aqueous solution contains a small proportion of OH ions and the concerned basic radical along with a large proportion of undissociated molecules of the base. e.g. NH4OH.
In simple words: A weak base is a base that only partially dissociates in water, leading to a small amount of hydroxide ions and many undissociated base molecules.
🎯 Exam Tip: Weak bases, like weak acids, are characterized by their incomplete dissociation in water, maintaining a significant amount of the original base molecules.
Question 7. Alkali
Answer: The bases which are highly soluble in water are called alkali, e.g. NaOH, KOH, NH3. Here, NaOH and KOH are strong alkalis while NH3 is a weak alkali.
In simple words: An alkali is a base that can dissolve readily in water, such as sodium hydroxide or potassium hydroxide.
🎯 Exam Tip: Remember the critical distinction: all alkalis are bases, but not all bases are alkalis; an alkali specifically refers to a water-soluble base.
Question 8. Basicity of acids
Answer: The number of H+ ions obtainable by the dissociation of one molecule of an acid is called its basicity.
In simple words: Basicity of an acid tells you how many hydrogen ions (H+) one molecule of that acid can release when it dissociates.
🎯 Exam Tip: Basicity is a measure of an acid's proton-donating capacity, directly impacting how much base it can neutralize.
Question 9. Acidity of bases
Answer: The number of OH ions obtainable by the dissociation of one molecule of a base is called its acidity.
In simple words: Acidity of a base describes how many hydroxide ions (OH-) one molecule of that base can release when it dissociates.
🎯 Exam Tip: Acidity of a base indicates its hydroxide-donating capacity, which determines its ability to neutralize acids.
Question 10. Concentration of solute in the solution.
Answer: The proportion of a solute in a solution is called the concentration of the solute in the solution.
In simple words: Concentration describes how much of a substance (solute) is present in a given amount of liquid mixture (solution).
🎯 Exam Tip: Concentration is a quantitative measure that helps compare the relative amounts of solute in different solutions.
Question 11. Concentrated solution.
Answer: When the concentration of a solute in its solution is high, it is a concentrated solution.
In simple words: A concentrated solution has a large amount of solute dissolved in a given amount of solvent.
🎯 Exam Tip: Understand that "concentrated" is a relative term; a solution is concentrated if it has a high proportion of solute compared to the solvent.
Question 12. Dilute solution
Answer: When the concentration of a solute in its solution is low, it is a dilute solution.
In simple words: A dilute solution contains only a small amount of solute dissolved in a large amount of solvent.
🎯 Exam Tip: "Dilute" also implies a relative measure, indicating a low proportion of solute within the solution.
Question 13. Neutralization
Answer: A reaction in which an acid reacts with a base to form salt and water is called a neutralization reaction.
NaOH + HCl → NaCl + H2O
Base + Acid → Salt + Water
In simple words: Neutralization is a chemical reaction where an acid and a base combine to produce a salt and water, effectively canceling out their acidic and basic properties.
🎯 Exam Tip: The core of neutralization is the reaction between H+ ions from the acid and OH- ions from the base to form water.
Question 14. Cathode
Answer: The electrode connected to the negative terminal of a battery by means of a conducting wire is called a cathode.
In simple words: The cathode is the negatively charged electrode in an electrochemical cell, attracting positive ions.
🎯 Exam Tip: Remember "Cathode is Negative" to recall its charge and that reduction (gain of electrons) occurs there.
Question 15. Anode
Answer: The electrode connected to the positive terminal of a battery by means of a conducting wire is called an anode.
In simple words: The anode is the positively charged electrode in an electrochemical cell, attracting negative ions.
🎯 Exam Tip: Remember "Anode is Positive" to recall its charge and that oxidation (loss of electrons) occurs there.
Question 16. Cations
Answer: Cations are positively charged ions which are attracted towards negative electrode (cathode) when electricity is passed into a solution of an ionic compound.
In simple words: Cations are positively charged ions that are drawn towards the negative electrode (cathode) during electrolysis.
🎯 Exam Tip: A simple mnemonic is "Cat-ions are Paws-itive" (positive) and are attracted to the cathode (negative).
Question 17. Anions
Answer: Anions are negatively charged ions which are attracted towards the positive electrode (anode) when electricity is passed into a solution of an ionic compound.
In simple words: Anions are negatively charged ions that are drawn towards the positive electrode (anode) during electrolysis.
🎯 Exam Tip: Anions are "Negative" and are attracted to the "Anode" (positive).
Question 18. Electrolytic cell
Answer: An assembly that consists of a container with an electrolyte and the electrodes dipped in it, is called an electrolytic cell.
In simple words: An electrolytic cell is a setup where electricity is used to drive a non-spontaneous chemical reaction, involving an electrolyte and two electrodes.
🎯 Exam Tip: The key components of an electrolytic cell are the electrolyte (ionic solution), electrodes (cathode and anode), and an external power source.
Question 19. Molarity of a solution
Answer: The number of moles of the solute dissolved in one litre of the solution is called the molarity of that solution. The molarity of a solute is indicated by writing its molecular formula inside a square bracket for example [NaCl] = 1
In simple words: Molarity is a measure of concentration that tells you the number of moles of a substance dissolved in one liter of a solution.
🎯 Exam Tip: Molarity (M) is a common unit of concentration in chemistry, calculated as moles of solute divided by liters of solution; [NaCl] = 1M means 1 mole of NaCl per liter.
Question 20. Acid - base indicators
Answer: Some natural and synthetic dyes show two different colours in acidic and basic solution, and such dyes are acid base indicators.
In simple words: Acid-base indicators are special dyes that change color depending on whether they are in an acidic or basic solution.
🎯 Exam Tip: Indicators are crucial for determining the pH range of a solution and for titrations; common examples include litmus, phenolphthalein, and methyl orange.
Explain the following chemical reactions with the help of balanced equations:
Question 1. Magnesium reacts with dilute hydrochloric acid.
Answer: When magnesium reacts with dilute hydrochloric acid, it forms magnesium chloride and hydrogen gas is liberated.
\(Mg_{(s)} + 2HCl_{(aq)} \implies MgCl_{2 (aq)} + H_{2 (g)}\)
Magnesium Hydrochloric Magnesium Hydrogen
acid chloride
In simple words: Magnesium metal reacts with hydrochloric acid to produce magnesium chloride salt and hydrogen gas.
🎯 Exam Tip: This is a single displacement reaction where a more reactive metal (magnesium) displaces hydrogen from an acid.
Question 2. When copper reacts with nitric acid.
Answer: When copper reacts with nitric acid, it forms copper nitrate and hydrogen gas is liberated.
\(Cu_{(s)} + 2HNO_{3 (aq)} \implies Cu(NO_3)_{2 (aq)} + H_{2 (g)}\)
Copper Nitric acid Copper Hydrogen
nitrate
In simple words: Copper reacts with nitric acid to yield copper nitrate and hydrogen gas.
🎯 Exam Tip: Remember that copper, being less reactive than hydrogen, reacts with nitric acid in a specific way, often producing nitrogen oxides depending on acid concentration, though here it's simplified to hydrogen gas.
Question 3. When ferric oxide reacts with diluted hydrochloric acid.
Answer: When Ferric oxide reacts with diluted hydrochloric acid, it forms ferric chloride and water.
\(ZnO_{(s)} + 2HCl_{(aq)} \implies ZnCl_{2 (aq)} + H_2O_{(l)}\)
Zinc Hydrochloric Zinc Water
oxide acid chloride
In simple words: Ferric oxide, a basic oxide, reacts with dilute hydrochloric acid to produce zinc chloride salt and water.
🎯 Exam Tip: This is an acid-base reaction where a metal oxide (basic in nature) reacts with an acid to form salt and water.
Question 4. When calcium oxide reacts with dilute hydrochloric acid.
Answer: When calcium oxide reacts with dilute hydrochloric acid, it forms calcium chloride and water.
In simple words: Calcium oxide reacts with dilute hydrochloric acid to produce calcium chloride and water.
🎯 Exam Tip: Recall that metal oxides are generally basic and react with acids in a neutralization type reaction.
Question 5. When Magnesium oxide reacts with dilute hydrochloric acid.
Answer:When magnesium oxide reacts with dilute hydrochloric acid, it forms magnesium chloride and water.
\( \text{MgO(s)} + \text{2HCl(aq)} \implies \text{MgCl2(aq)} + \text{H2O(l)} \)
Magnesium Hydrochloric Magnesium Water
oxide acid chloride
In simple words: Magnesium oxide reacts with hydrochloric acid to form magnesium chloride and water, which is a neutralization reaction.
🎯 Exam Tip: Remember to balance chemical equations and correctly identify the products of metal oxide-acid reactions for full marks.
Question 6. When zinc oxide reacts with dilute hydrochloric acid.
Answer:When zinc oxide reacts with dilute hydrochloric acid, it forms zinc chloride and water.
\( \text{ZnO(s)} + \text{2HCl(aq)} \implies \text{ZnCl2(aq)} + \text{H2O(l)} \)
Zinc Hydrochloric Zinc Water
oxide acid chloride
In simple words: Zinc oxide reacts with hydrochloric acid to produce zinc chloride and water, exemplifying a neutralization reaction.
🎯 Exam Tip: Pay attention to the valencies of elements when writing chemical formulas and balancing equations.
Question 7. When aluminium oxide reacts with hydrogen fluoride
Answer:When aluminium oxide reacts with hydrogen fluoride, it forms Aluminium fluoride arid water.
\( \text{Al2O3(s)} + \text{6HF(l)} \implies \text{2AlF3(aq)} + \text{3H2O(l)} \)
Aluminium Hydrogen Aluminium Water
oxide fluoride fluoride
In simple words: Aluminium oxide reacts with hydrogen fluoride to yield aluminium fluoride and water.
🎯 Exam Tip: Understand that metal oxides can react with acids to form salts and water, a key characteristic of basic oxides.
Question 8. When carbon dioxide reacts with sodium hydroxide.
Answer:When carbon dioxide reacts with Sodium hydroxide, it forms Sodium carbonate and water.
\( \text{CO2(g)} + \text{2NaOH(aq)} \implies \text{Na2CO3(aq)} + \text{H2O(l)} \)
Carbon Sodium Sodium Water
dioxide hydroxide carbonate
In simple words: Carbon dioxide, an acidic oxide, reacts with sodium hydroxide (a base) to form sodium carbonate and water in a neutralization reaction.
🎯 Exam Tip: Recognize that non-metal oxides are generally acidic and react with bases to form salt and water.
Question 9. When carbon dioxide reacts with potassium hydroxide.
Answer:When carbon dioxide reacts with potassium hydroxide, it forms potassium carbonate and water.
\( \text{CO2(g)} + \text{2KOH(aq)} \implies \text{K2CO3(aq)} + \text{H2O(l)} \)
Carbon Potassium Potassium Water
dioxide hydroxide carbonate
In simple words: Carbon dioxide reacts with potassium hydroxide to form potassium carbonate and water.
🎯 Exam Tip: Similar to sodium hydroxide, potassium hydroxide is a strong base that reacts with acidic oxides like carbon dioxide.
Question 10. When sulphur trioxide reacts with sodium hydroxide.
Answer:When sulphur trioxide reacts with sodium hydroxide, it forms sodium sulphate and water.
\( \text{SO3(g)} + \text{2NaOH(aq)} \implies \text{Na2SO4(aq)} + \text{H2O(l)} \)
Sulphur Sodium Sodium Water
trioxide hydroxide sulphate
In simple words: Sulphur trioxide, another acidic oxide, reacts with sodium hydroxide to produce sodium sulphate and water.
🎯 Exam Tip: Remember that sulphur trioxide is a gas and a strong acidic oxide, its reaction with bases is crucial in industrial processes.
Question 11. When calcium hydroxide reacts with carbon dioxide.
Answer:When calcium hydroxide reacts with carbon dioxide, it forms calcium carbonate and water.
\( \text{Ca(OH)2(aq)} + \text{CO2(g)} \implies \text{CaCO3(s)} + \text{H2O(l)} \)
Calcium Carbon Calcium Water
hydroxide dioxide carbonate
In simple words: Calcium hydroxide (limewater) reacts with carbon dioxide to form insoluble calcium carbonate, causing the solution to turn milky.
🎯 Exam Tip: This reaction is commonly used as a test for carbon dioxide gas, indicated by the formation of a white precipitate.
Question 12. When sodium carbonate reacts with hydrochloric acid.
Answer:When sodium carbonate reacts with hydrochloric acid, it forms sodium chloride, carbon dioxide and water.
\( \text{Na2CO3(s)} + \text{2HCl(aq)} \implies \text{2NaCl(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
Sodium Hydrochloric Sodium Carbon Water
carbonate acid chloride dioxide
In simple words: Sodium carbonate reacts with hydrochloric acid to produce sodium chloride, carbon dioxide, and water.
🎯 Exam Tip: Reactions of carbonates with acids always produce carbon dioxide gas, a salt, and water.
Question 13. When sodium carbonate reacts with sulphuric acid.
Answer:When sodium carbonate reacts with sulphuric acid, it forms sodium sulphate, carbon dioxide and water.
\( \text{Na2CO3(s)} + \text{H2SO4(aq)} \implies \text{Na2SO4(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
Sodium Sulphuric Sodium Carbon Water
carbonate acid sulphate dioxide
In simple words: Sodium carbonate reacts with sulphuric acid, yielding sodium sulphate, carbon dioxide, and water.
🎯 Exam Tip: This is another example of a carbonate reacting with an acid, demonstrating the consistent production of carbon dioxide.
Question 14. When calcium carbonate reacts with nitric acid.
Answer:When calcium carbonate reacts with nitric acid, it forms calcium nitrate, carbon dioxide and water.
\( \text{CaCO3(s)} + \text{2HNO3(aq)} \implies \text{Ca(NO3)2(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
Calcium Nitric Calcium Carbon Water
carbonate acid nitrate dioxide
In simple words: Calcium carbonate reacts with nitric acid to form calcium nitrate, carbon dioxide, and water.
🎯 Exam Tip: All carbonates, whether sodium or calcium, follow the same reaction pattern with acids: salt, water, and carbon dioxide.
Question 15. When potassium carbonate reacts with sulphuric acid.
Answer:When potassium carbonate reacts with sulphuric acid, it forms potassium sulphate, carbon dioxide and water.
\( \text{K2CO3(s)} + \text{H2SO4(aq)} \implies \text{K2SO4(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
Potassium Sulphuric Potassium Carbon Water
carbonate acid sulphate dioxide
In simple words: Potassium carbonate reacts with sulphuric acid to produce potassium sulphate, carbon dioxide, and water.
🎯 Exam Tip: Remember to write balanced chemical equations for these reactions, as balancing coefficients are critical for stoichiometry.
Question 16. When sodium bicarbonate reacts with hydrochloric acid. OR Dilute HCl was poured on baking soda
Answer:When sodium bicarbonate reacts with hydrochloric acid, it forms sodium chloride, carbon dioxide and water.
\( \text{NaHCO3(s)} + \text{HCl(aq)} \implies \text{NaCl(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
Sodium Hydrochloric Sodium Carbon Water
bicarbonate acid chloride dioxide
In simple words: Baking soda (sodium bicarbonate) reacts with hydrochloric acid to release carbon dioxide gas, along with sodium chloride and water.
🎯 Exam Tip: This is a common household reaction, often used to produce carbon dioxide quickly, and it's a good example of a weak acid-base reaction.
Question 17. When potassium bicarbonate reacts with nitric acid.
Answer:When potassium bicarbonate reacts with nitric acid, it forms potassium nitrate, carbon dioxide and water.
\( \text{KHCO3(s)} + \text{HNO3(aq)} \implies \text{KNO3(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
Potassium Nitric Potassium Carbon Water
bicarbonate acid nitrate dioxide
In simple words: Potassium bicarbonate reacts with nitric acid to yield potassium nitrate, carbon dioxide, and water.
🎯 Exam Tip: All bicarbonates react similarly with acids, producing a salt, water, and carbon dioxide gas.
Question 18. When sodium bicarbonate reacts with acetic acid.
Answer:When sodium bicarbonate reacts with acetic acid, it forms sodium acetate, carbon dioxide and water.
\( \text{NaHCO3(s)} + \text{CH3COOH(aq)} \implies \text{CH3COONa(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
Sodium Acetic Sodium Carbon Water
bicarbonate acid acetate dioxide
In simple words: Sodium bicarbonate reacts with acetic acid to produce sodium acetate, carbon dioxide, and water.
🎯 Exam Tip: Even weak acids like acetic acid can react with bicarbonates to produce carbon dioxide, which is why vinegar and baking soda foam up.
Question 19. When copper sulphate is heated.
Answer:When copper sulphate is heated it loses it's water of crystallization to form white anhydrous copper sulphate.
\( \text{CuSO4} \cdot \text{5 H2O} \xrightarrow{\text{Heat}} \text{CuSO4} + \text{5 H2O} \)
Copper (blue) (White) Water
sulphate crystalline anhydrous
Copper sulphate
In simple words: Heating blue copper sulphate crystals removes their water of crystallization, turning them into white anhydrous copper sulphate.
🎯 Exam Tip: This is a common experiment to demonstrate water of crystallization and a reversible physical change. Note the color change from blue to white.
Question 20. When Ferrous sulphate is heated.
Answer:When ferrous sulphate is heated it loses its water of crystallization to form white anhydrous ferrous sulphate.
\( \text{FeSO4} \cdot \text{7 H2O} \xrightarrow{\text{Heat}} \text{FeSO4} + \text{7H2O} \)
Ferrous Anhydrous Water
sulphate (green) Ferrous sulphate
crystalline (White)
In simple words: Heating green ferrous sulphate crystals causes them to lose their water of crystallization, forming white anhydrous ferrous sulphate.
🎯 Exam Tip: Similar to copper sulphate, ferrous sulphate also demonstrates water of crystallization, with a color change from green to white upon heating.
Complete The Following Table
Question 1. Complete the following table.
Answer:
Acid: Number of H+ obtained from one molecule.
| HCl | HNO3 | H2SO4 | H2CO3 | H3BO3 | H3PO4 | CH3COOH |
| 1 | 1 | 2 | 2 | 3 | 3 | 1 |
Base: Number of OH- ions obtained from one molecule
| NaOH | KOH | Ca(OH)2 | Ba(OH)2 | Al(OH)3 | Fe(OH)3 | NH4OH |
| 1 | 1 | 2 | 2 | 3 | 3 | 1 |
In simple words: This table categorizes acids and bases by their basicity (number of H+ ions released) and acidity (number of OH- ions released) respectively, which determines their strength and type.
🎯 Exam Tip: Memorizing the basicity/acidity of common acids and bases is essential for understanding their chemical behavior and for exam questions.
Complete The Following Reactions
Question 1.
Answer:\( \text{NH3(g)} + \text{H2O(l)} \implies \text{NH4+(aq)} + \text{OH-(aq)} \)
\( \text{Na2O(s)} + \text{H2O(l)} \implies \text{2Na+(aq)} + \text{2OH-(aq)} \)
\( \text{CaO(s)} + \text{H2O(l)} \implies \text{Ca2+(aq)} + \text{2OH-(aq)} \)
In simple words: These reactions show how ammonia, sodium oxide, and calcium oxide react with water to form their respective basic solutions.
🎯 Exam Tip: Understand that metal oxides often react with water to form bases, releasing hydroxide ions, while non-metal oxides react with water to form acids.
Question 2. Metal + Dilute acid → Salt + Hydrogen
Answer:\( \text{Mg(s)} + \text{2HCl(aq)} \implies \text{MgCl2(aq)} + \text{H2(g)} \)
\( \text{Zn(s)} + \text{H2SO4(aq)} \implies \text{ZnSO4(aq)} + \text{H2(g)} \)
\( \text{Cu(s)} + \text{2HNO3(aq)} \implies \text{Cu(NO3)2(aq)} + \text{H2(g)} \)
In simple words: Reactive metals like magnesium and zinc react with dilute acids to produce a salt and hydrogen gas, while copper reacts with nitric acid in a similar way.
🎯 Exam Tip: The reactivity series of metals determines whether a metal can displace hydrogen from an acid. Remember to balance these single displacement reactions.
Question 3. Metal oxide + Dilute acid → Salt + Water
Answer:\( \text{CaO(s)} + \text{2HCl(aq)} \implies \text{CaCl2(aq)} + \text{H2O(l)} \)
\( \text{MgO(s)} + \text{2HCl(aq)} \implies \text{MgCl2(aq)} + \text{H2O(l)} \)
\( \text{ZnO(s)} + \text{2HCl(aq)} \implies \text{ZnCl2(aq)} + \text{H2O(l)} \)
\( \text{Al2O3(s)} + \text{6HF(l)} \implies \text{2AlF3(aq)} + \text{3H2O(l)} \)
\( \text{Fe2O3(s)} + \text{6HCl(aq)} \implies \text{2FeCl3(aq)} + \text{3H2O(l)} \)
In simple words: Metal oxides react with dilute acids to form a salt and water, which is a characteristic neutralization reaction for basic oxides.
🎯 Exam Tip: These reactions are examples of acid-base neutralization, where the metal oxide acts as a base. Ensure correct salt formation based on valencies.
Question 4. Oxide of non-metal + base → salt + water
Answer:\( \text{CO2(g)} + \text{2NaOH(aq)} \implies \text{Na2CO3(aq)} + \text{H2O(l)} \)
\( \text{CO2(g)} + \text{2KOH(aq)} \implies \text{K2CO3(aq)} + \text{H2O(l)} \)
\( \text{SO3(g)} + \text{2NaOH(aq)} \implies \text{Na2SO4(aq)} + \text{H2O(l)} \)
In simple words: Non-metal oxides, which are acidic, react with bases to form a salt and water, a classic neutralization pattern.
🎯 Exam Tip: Remember that non-metal oxides like CO2 and SO3 are acidic and will neutralize bases to form the corresponding salt and water.
Question 5. Carbonate salt of metal + dilute acid → Another salt of metal + Carbon dioxide + water
Answer:\( \text{Na2CO3(s)} + \text{2HCl(aq)} \implies \text{2NaCl(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
\( \text{Na2CO3(s)} + \text{H2SO4(aq)} \implies \text{Na2SO4(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
\( \text{CaCO3(s)} + \text{2HNO3(aq)} \implies \text{Ca(NO3)2(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
\( \text{K2CO3(s)} + \text{H2SO4(aq)} \implies \text{K2SO4(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
In simple words: Metal carbonates react with dilute acids to produce a new salt, carbon dioxide gas, and water.
🎯 Exam Tip: This type of reaction is easily identified by the evolution of carbon dioxide gas (effervescence) and is a common test for carbonates.
Question 6. Bicarbonate salt of metal + dilute acid → Another salt of metal + carbon dioxide + water
Answer:1. \( \text{NaHCO3(s)} + \text{HCl(aq)} \implies \text{NaCl(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
2. \( \text{KHCO3(s)} + \text{HNO3(aq)} \implies \text{KNO3(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
3. \( \text{NaHCO3(s)} + \text{CH3COOH(aq)} \implies \text{CH3COONa(aq)} + \text{CO2(g)} + \text{H2O(l)} \)
In simple words: Bicarbonate salts of metals react with dilute acids to form a new salt, carbon dioxide gas, and water.
🎯 Exam Tip: Bicarbonates behave similarly to carbonates in reactions with acids, always producing CO2 and water, making them effective antacids.
Give Scientific Reasons:
Question 1. Ionic compound NaCl has very high stability.
Answer:- The outermost shell of both Na⁺ and Cl¯ ions is a complete octet.
- An electronic configuration with a complete octet indicates a stable state.
- A molecule of NaCl has Na⁺ and Cl¯ ions. An ionic bond is formed between these ions.
- The force of attraction between them is very strong as it is formed between the oppositely charged Na⁺ and Cl¯ ions.
- Therefore NaCl, an ionic compound has very high stability.
In simple words: Sodium chloride is very stable because its ions (Na+ and Cl-) have complete outer electron shells and are held together by strong electrostatic forces in an ionic bond.
🎯 Exam Tip: High stability in ionic compounds like NaCl is attributed to the strong electrostatic attraction between oppositely charged ions and the attainment of stable octet configurations.
Question 2. Ionic compound dissociates while forming an aqueous solution.
Answer:- On dissolving in water, an ionic compound forms an aqueous solution.
- In the solid state, the oppositely charged ions in the ionic compound are sitting side by side.
- When an ionic compound begins to dissolve in water, the water molecules push themselves in between the ions of the compound and it separates them from each other, that is to say, an ionic compound dissociates while forming an aqueous solution.
In simple words: Water molecules pull apart the individual ions of an ionic compound, allowing them to move freely and form an aqueous solution.
🎯 Exam Tip: This dissociation process is crucial for ionic compounds to conduct electricity in solution, as it releases free-moving charged particles.
Question 3. Blue coloured copper sulphate crystals become colourless on heating.
Answer:- Copper sulphate crystals are blue in colour and crystalline in form due to presence of water of crystallisation.
- Each molecule of crystalline copper sulphate contains five molecules of water of crystallisation (CuSO4.5H2O).
- On heating, the copper sulphate crystals lose the water of crystallisation and turns into white amorphous powder called as anhydrous copper sulphate.
- Therefore, blue coloured copper sulphate crystals become colourless on heating.
In simple words: Copper sulphate crystals are blue due to water molecules trapped within their structure; heating removes this water, turning them white and amorphous.
🎯 Exam Tip: The color change of hydrated copper sulphate is a classic example of a reversible physical change related to water of crystallization.
Question 4. During electrolysis of water, a few drops of sulphuric acid are added to it.
Answer:- Pure water is a covalent compound and hence it is a non-electrolyte and does not conduct electricity.
- When a few drops of sulphuric acid (H2SO4) are added to water.
- Being a strong acid it dissociates almost completely in its solution forming H⁺ cations and SO4²- anions.
- The movement of these ions in the solution towards the respective electrodes amount to the conduction of electricity through the solution.
- Therefore, during electrolysis of water, a few drops of sulphuric acid are added to it.
In simple words: Sulphuric acid is added to water during electrolysis because pure water is a poor conductor; the acid dissociates into ions, making the solution conductive for the process.
🎯 Exam Tip: Adding an electrolyte like sulphuric acid increases the concentration of ions in water, enabling efficient conduction of electricity for electrolysis.
Question 5. Glucose is a non-electrolyte.
Answer:- Glucose is a covalent compound
- It does not form any ions in its aqueous solution.
- Due to this aqueous solution of glucose does not conduct electronic current.
- Hence, glucose is a non-electrolyte.
In simple words: Glucose is a non-electrolyte because it's a covalent compound that doesn't produce ions when dissolved in water, thus preventing it from conducting electricity.
🎯 Exam Tip: Non-electrolytes are typically covalent compounds that dissolve without dissociating into ions, distinguishing them from ionic compounds and strong acids/bases.
Question 6. Pure water is a poor conductor of electricity but aqueous solution of sodium chloride conducts electricity.
Answer:- Pure water does not contain any free ions.
- Sodium chloride (NaCl) is an ionic compound made up of sodium cation (Na+) and chloride anion (Cl-)
- When sodium chloride is dissolved in water, these ions dissociates in its aqueous solution. '
- These ions are free to move in the solution and conduct electricity.
- Therefore, pure water is a poor conductor of electricity but aqueous solution of sodium Chloride conducts electricity.
In simple words: Pure water lacks free ions to conduct electricity, but adding sodium chloride provides mobile Na+ and Cl- ions, making the solution an electrical conductor.
🎯 Exam Tip: Electrical conductivity in solutions depends on the presence of free-moving ions; pure covalent substances are non-conductors, while dissolved ionic compounds are conductors.
Question 7. When carbon dioxide gas is passed through freshly prepared lime water, the limewater turns milky.
Answer:- Limewater traditionally means a weak solution of the alkali calcium hydroxide Ca(OH)2.
- When CO2 is passed through limewater, it reacts with calcium hydroxide to form insoluble particulates (precipitate of calcium carbonate (CaCO3).
- Calcium carbonate is weak basic salt and this gives a milky white precipitate
\( \text{CO2} + \text{Ca(OH)2} \implies \text{CaCO3} \downarrow + \text{H2O} \)
Carbon Calcium Calcium
dioxide hydroxide Carbonate
(lime water)
- Hence, lime water turns milky when CO2 gas is passed through it.
In simple words: Limewater turns milky when carbon dioxide is passed through it because calcium carbonate, an insoluble white precipitate, is formed.
🎯 Exam Tip: This reaction is a fundamental chemical test for carbon dioxide, where the formation of a white precipitate (CaCO3) signifies its presence.
Q.3.1. Answer The Following:
Question 1. Write down chemical equations for
(a) Zinc oxide reacts with sodium hydroxide
(b) Aluminium oxide reacts with sodium hydroxide.
Answer:(a) When zinc oxide reacts with sodium hydroxide, it forms sodium zincate and water
\( \text{ZnO} + \text{2NaOH} \implies \text{Na2ZnO2} + \text{H2O} \)
zinc sodium sodium water
oxide hydroxide zincate
(b) When Aluminium oxide reacts with sodium hydroxide, it forms sodium aluminate and water.
\( \text{Al2O3} + \text{2NaOH} \implies \text{2NaAlO2} + \text{H2O} \)
aluminium sodium sodium water
oxide hydroxide aluminate
In simple words: Both zinc oxide and aluminium oxide react with sodium hydroxide to form their respective soluble salts (sodium zincate and sodium aluminate) and water, showcasing their amphoteric nature.
🎯 Exam Tip: These reactions demonstrate the amphoteric nature of ZnO and Al2O3, meaning they can react with both acids and strong bases.
Question 2. Can we call Al2O3 and ZnO acidic oxides on the basis of above reactions.
Answer:- No, because they also react with acids to form their respective salts and water.
- So, they show the properties of basic oxides also.
In simple words: No, Al2O3 and ZnO are not solely acidic oxides; they are amphoteric because they can also react with acids, demonstrating properties of basic oxides.
🎯 Exam Tip: Amphoteric oxides react with both acids and bases. If they only reacted with bases, they would be considered acidic; if only with acids, they would be basic.
Question 3. Define 'amphoteric oxides' and give two examples.
Answer:- Amphoteric oxides are those oxides which react with both adds as well as bases to form their respective salts and water.
- Amphoteric oxides show the properties of both acidic oxides as well as basic oxides. ZnO and Al2 O3 are amphoteric oxides.?
In simple words: Amphoteric oxides are compounds that can act as both an acid and a base, reacting with strong acids and strong bases to form salts and water. Examples include zinc oxide (ZnO) and aluminium oxide (Al2O3).
🎯 Exam Tip: Understanding amphoteric behavior is key to predicting reactions of certain metal oxides. Remember that they neutralize both strong acids and strong bases.
Question 4. Take a solution of 1g copper sulphate in 50ml water in a 100 ml capacity beaker. Use a thick plate of copper as anode and a carbon rod as cathode. Arrange the apparatus as shown in the figure and pass an electric current through the circuit for some time. Do you see any changes?
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र इलेक्ट्रोलाइटिक सेल में कॉपर सल्फेट के घोल में विद्युत चालकता का परीक्षण दिखा रहा है। इसमें एक बीकर में कॉपर सल्फेट का घोल है, जिसमें एक तांबे का एनोड और एक कार्बन कैथोड डूबा हुआ है, जो एक बैटरी और स्विच के माध्यम से बल्ब से जुड़े हैं।
- A thin film of copper metal is deposited on cathode which is immersed in solution. There is no change in colour of solution
- The electrons from cathode combines with Cu2+ ion from the solution forming Cu atoms which were then deposited on the cathode.
In simple words: During the electrolysis of copper sulphate solution with a copper anode and carbon cathode, copper metal deposits on the cathode as Cu2+ ions gain electrons, while the solution's color remains unchanged as the copper anode continuously replenishes Cu2+ ions.
🎯 Exam Tip: In electrolysis, understand the reactions occurring at both anode and cathode. Copper deposition on the cathode is a key observation for copper salt solutions.
Q.3.5. Answer In Brief:
Question 1. What are acids, bases and salts?
Answer:- Compounds having H+ as the basic radical in their molecules are called Acids.
- Compounds having OH- as the acidic radical in their molecule are called Bases.
- Ionic compounds which have a basic radical other than H+ and an acidic radical other than OH- are called salts.
In simple words: Acids release H+ ions, bases release OH- ions, and salts are ionic compounds formed from a basic radical (not H+) and an acidic radical (not OH-).
🎯 Exam Tip: Clear definitions of acids, bases, and salts based on their ionic components (Arrhenius theory) are fundamental for chemistry exams.
Question 2. What is an ionic bond?
Answer:- The molecule of an ionic compound has two constituents namely cation (positive ion / basic radical) and anion (negative ion / acidic radical).
- There is a force of attraction between these ions as they are oppositely charged, and that is called the ionic bond.
- The force of attraction between one positive charge on a cation and one negative charge on an anion makes one ionic bond.
In simple words: An ionic bond is a strong electrostatic force of attraction between oppositely charged ions (cations and anions) in an ionic compound.
🎯 Exam Tip: Emphasize the transfer of electrons and the resulting electrostatic attraction between positive and negative ions as the core of an ionic bond.
Question 3. Give examples to show that proportions of H⁺ and OH¯ ions in aqueous solution determines the properties of those solutions.
Answer:The examples to show that proportions of H⁺ and OH¯ ions in aqueous solution determines the properties of those solutions are :
- The proportions of H⁺ and OH ions divides soil into the acidic, neutral and basic, types of soil.
- It is necessary for blood, cell sap etc to have H+ and OH- ions in certain definite proportions for their proper functioning.
- Fermentation carried out with the help of micro-organisms, other biochemical processes and also many chemical processes require the proportion of H⁺ and OH- ions to be maintained within certain limits.
In simple words: The balance of H+ and OH- ions dictates the acidity or basicity of solutions, influencing crucial environmental factors like soil pH, and biological processes such as blood pH and fermentation.
🎯 Exam Tip: Connect H+ and OH- ion concentrations to pH, and demonstrate practical implications in biological systems (e.g., blood pH, enzyme activity) and environmental contexts (e.g., soil fertility).
Question 4. What is pH scale?
Answer:1. In 1909, the Danish scientist Sorensen introduced a convenient new scale of expressing H+ ion concentration which is found to be useful in chemical and biochemical processes.
2. It is the pH scale (pH: power of hydrogen). The pH scale extends from 0 to 14. According to this scale pure water has a pH of 7. pH 7 indicates a neutral solution. This pH is the midpoint of the scale.
3. The pH of an acidic solution is less than 7 and?
In simple words: The pH scale, introduced by Sorensen, is a numerical scale from 0 to 14 that indicates the acidity or basicity of a solution, where pH 7 is neutral, below 7 is acidic, and above 7 is basic.
🎯 Exam Tip: Define pH and its range, clearly stating what pH values indicate for acidic, neutral, and basic solutions. Mention Sorensen's contribution.
Question 5. Give the pH of following solutions.
Answer:
| Solution | pH |
| Strong acids 1 M HCl | 0.0 |
| Gastric juice | 1.0 |
| Lemon juice | 2.5 |
| Vinegar | 3.0 |
| Tomato juice | 4.1 |
| Black coffee | 5.0 |
| Acid rain | 5.6 |
| Weak acids Urine | 6.0 |
| Neutral Rain, milk | 6.5 |
| Weak bases Pure water, sugar solution | 7.0 |
| Blood | 7.4 |
| Solution of baking soda | 8.5 |
| Toothpaste | 9.5 |
| Milk of magnesia | 10.5 |
| Lime water | 11.0 |
| Strong bases 1 M NaOH | 14.0 |
In simple words: This table provides the pH values for a range of common solutions, illustrating how pH varies from strongly acidic (0) to strongly basic (14), with pure water being neutral (7).
🎯 Exam Tip: Familiarity with the approximate pH values of common substances helps in understanding acidity/basicity and related concepts.
Question 6. What is universal indicator? Which is the most accurate method of measuring the pH of a solution?
Answer:- In the pH scale, the pH of solutions varies from 0 to 14 in accordance with the strength of the acid or base.
- To show these variations in pH, a universal indicator is used.
- A universal indicator shows different colours at different values of pH. A universal indicator is made by mixing several synthetic indicators in specific proportions.
- The pH of a solution can be determined by means of a universal indicator solution or the pH paper made from it.
- However, the most accurate method of measuring the pH of a solution is to use an electrical instrument called pH meter.
- In this method, pH is measured by dipping electrodes into the solution.
In simple words: A universal indicator is a mixture of dyes that displays different colors over a wide pH range, providing an estimate, while a pH meter offers the most accurate digital measurement of pH using electrodes.
🎯 Exam Tip: Differentiate between universal indicators (colorimetric, less precise) and pH meters (electronic, highly accurate) for measuring pH. Highlight the principle of each method.
Answer In Detail:
Question 1. Explain the Arrhenius theory of acids and bases.
Answer:The Swedish scientist Arrhenius put forth a theory of acids and bases in the year 1887. This theory gives definitions of acids and bases as follows:
Acid: An acid is a substance which on dissolving in water gives rise to H ion as the only cation. For example, HCl, H2SO4, H2CO3
\( \text{HCl(g)} \xrightarrow{\text{Water dissociation}} \text{H+(aq)} + \text{Cl-(aq)} \)
\( \text{H2SO4(l)} \xrightarrow{\text{Water dissociation}} \text{H+(aq)} + \text{HSO4-(aq)} \)
\( \text{HSO4-(aq)} \xrightarrow{\text{dissociation}} \text{H+(aq)} + \text{SO4²-(aq)} \)
Base: A base is a substance which on dissolving in water gives rise to the OH ion as the only anion, For example, NaOH, Ca(OH)2
\( \text{NaOH(s)} \xrightarrow{\text{Water dissociation}} \text{Na+(aq)} + \text{OH-(aq)} \)
\( \text{Ca(OH)2(s)} \xrightarrow{\text{Water dissociation}} \text{Ca2+(aq)} + \text{2OH-(aq)} \)
In simple words: The Arrhenius theory defines an acid as a substance that produces H+ ions when dissolved in water, and a base as a substance that produces OH- ions when dissolved in water.
🎯 Exam Tip: State Arrhenius's definitions clearly, provide one example for each (acid and base) with their dissociation equations in water.
Question 2. Write a short note on Neutralization.
Answer:- Take 10 ml of dilute HCl in a beaker, go on adding dilute NaOH drop by drop and record the pH.
- Stop adding the NaOH when the green colour appears on the pH paper, that is when the pH of solution becomes 7.
- Both HCl and NaOH dissociate in their aqueous solutions.
- Addition of NaOH to HCl solution is like adding a large concentration of OH ions to a large concentration of H+ ions.
- However water dissociates into H⁺ and OH ions to a very small extent.
- Therefore on mixing the excess OH- ions combines with excess H+ ions and forms H2O molecules which mix with solvent water.
- This change can be represented by the ionic equation shown as follows. H+ + Cl- + Na+ + OH- → Na+ + Cl- + H2O
- It can be observed that Na+ and CT ions are there on both the sides.
Therefore the net ionic reaction is H+ + OH- → H2O
- As NaOH solution is added drop by drop to the HCl solution, the concentration of ff goes on decreasing due to combination with added OH ions, and that is how the pH goes on increasing.
- When enough NaOH is added to HCl, the resulting aqueous solution contains only Na⁺ and Cl- ions, that is, NaCl, a salt, and the solvent water. The only source of H⁺ and OH- ions in this solution is a dissociation of water.
- Therefore, this reaction is called the Neutralization reaction. The Neutralization reaction is also represented by the following simple equation.
\( \text{HCl} + \text{NaOH} \implies \text{NaCl} + \text{H2O} \)
acid + base salt + water
In simple words: Neutralization is a chemical reaction where an acid and a base react to form a salt and water, typically resulting in a solution with a pH of 7 when equal molar amounts are used.
🎯 Exam Tip: Define neutralization, explain the ionic changes (H+ and OH- combining to form water), and provide a balanced chemical equation for a strong acid-strong base reaction.
Question 3. Explain the water of Crystallization.
Answer:
• Take some crystals of blue vitriol \((\text{CuSO}_4\text{. 5H}_2\text{O})\) in a test tube. Heat the test tube on a low flame of a burner.
• It was observed that on heating, the crystalline structure of blue vitriol broke down to form a colourless powder and water came out.
• This water was part of the crystal structure of blue vitriol. It is called water of crystallization.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र क्रिस्टलीकरण के जल के गुणों को दर्शाता है। इसमें एक टेस्ट ट्यूब में नीले रंग का कॉपर सल्फेट रखा है जिसे गर्म करने पर वह रंगहीन हो जाता है और जल की बूंदें निकलती हैं। फिर, जल मिलाने पर वह वापस नीला हो जाता है।
• was formed which had the same colour as the solution in the first test tube.
• From this we come to know that no chemical change has occurred in the crystals of blue vitriol due to heating.
• Losing water on heating blue vitriol, breaking down of the crystal structure, losing blue colour and regaining blue colour on adding water are all physical changes.
\( \text{CuSO}_4\text{. 5H}_2\text{O} \)
\( \implies^{\text{Heat}} \) \( \text{CuSO}_4 + \text{5H}_2\text{O} \)
(Blue) (White)
(anhydrous copper sulphate)
• Similarly, ferrous Sulphate crystals also contain 7 molecules of water of crystallization which are lost on heating.
• The reaction is represented as
\( \text{FeSO}_4\text{. 7H}_2\text{O} \)
\( \implies^{\text{Heat}} \) \( \text{FeSO}_4 + \text{7H}_2\text{O} \)
(Green) (White)
(anhydrous ferrous sulphate)
• Ionic compounds are crystalline in nature. These crystals are formed as a result of definite arrangement of ions.
• In the crystals of some compounds, water molecules are also included in this arrangement.
• That is the water of crystallization. The water of crystallization is present in a definite proportion of the chemical formula of the compound.In simple words: Water of crystallization refers to the definite number of water molecules that are chemically bound to the crystal structure of a salt. Upon heating, these crystals lose this water and change in appearance, and regain color upon re-addition of water.
🎯 Exam Tip: Understanding the concept of water of crystallization is crucial for explaining the physical changes observed in hydrated salts upon heating.
Question 4. Explain the conduction of electricity through solutions of ionic compounds
Answer:
1. Electrons conduct electricity through electrical wires, and ions conduct electricity through a liquid or a solution.
2. Electrons leave the battery at the negative terminal, complete the electric circuit and enter the battery at the positive terminal.
3. When there is a liquid or a solution in the circuit, two rods, wires or plates are immersed in it. These are called electrodes.
4. Electrodes are made of conducting solid. The electrode connected to negative terminal of a battery by means of a conducting wire is called a cathode and the electrode connected to the positive terminal of a battery is called anode.
5. We have seen that salts, strong acids and strong bases dissociates almost completely in their aqueous solutions.
6. Therefore the aqueous solutions of all these three contain large number of cations and anions.
7. A characteristic of liquid state is the mobility of its particles. Due to its mobility the positive charged ions of the solution are attracted to the negative electrode or cathode.
8. On the other hand, the negative charged ions of the solution are attracted to the positive electrode or anode.
9. The movement of ions in the solution towards the respective electrodes accounts to the conduction of electricity through the solution.
10. From this we can understand that those liquids or solutions which contain a large number of dissociated ions conduct electricity.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र सोडियम क्लोराइड के घोल में विद्युत चालकता का परीक्षण दर्शाता है। इसमें दो इलेक्ट्रोड एक बैटरी और बल्ब से जुड़े हैं, और इलेक्ट्रोड घोल में डूबे हुए हैं, जो आयनों की गति के कारण बल्ब को रोशन करते हैं।
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र जलीय घोल में आयनों के पृथक्करण को दर्शाता है। इसमें धनात्मक और ऋणात्मक आयन व्यवस्थित रूप से दिखाए गए हैं जो घोल में स्वतंत्र रूप से घूम रहे हैं, जिससे विद्युत प्रवाह संभव होता है।In simple words: Ionic compounds conduct electricity in solution because they dissociate into free-moving ions. These charged ions migrate towards oppositely charged electrodes, creating an electric current.
🎯 Exam Tip: Remember that for electrical conduction, the presence of free-moving charged particles (ions or electrons) is essential. Ionic compounds provide these ions in their aqueous solutions.
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