Maharashtra Board Class 8 Science Chapter 12 Introduction to Acid and Base Solutions

Std 8 Science Chapter 12 Introduction to Acid and Base Question Answer Maharashtra Board

Class 8 Science Chapter 12 Introduction to Acid and Base Question Answer Maharashtra Board

Question 1. Identify the following solutions, whether they are acid or base.

🎯 Exam Tip: When evaluating indicator questions, focus on specific color changes for each indicator in both acidic and basic environments to correctly identify the solution type. Pay close attention to the initial color of the indicator and how it reacts.

Question 2. Write chemical names from given formulae.
H2SO4, Ca(OH)2, HCI, NaOH, KOH, NH4OH
Answer:
1. H2SO4 - Sulphuric acid
2. Ca(OH)2 - Calcium hydroxide
3. HCl - Hydrochloric acid
4. NaOH - Sodium hydroxide
5. KOH - Potassium hydroxide
6. NH4OH - Ammonium hydroxide
In simple words: The chemical names correspond to the given formulas: H2SO4 is Sulphuric acid, Ca(OH)2 is Calcium hydroxide, HCl is Hydrochloric acid, NaOH is Sodium hydroxide, KOH is Potassium hydroxide, and NH4OH is Ammonium hydroxide. These are common acids and bases.

🎯 Exam Tip: Accurately identifying chemical names from formulas is fundamental. Practice associating common acid and base formulas with their correct names, paying attention to polyatomic ions and oxidation states.

Question 3. Sulphuric acid has highest importance in chemical Industry. Why?

Answer:
Sulphuric acid has highest importance in the chemical industry because it is used in the manufacturing of fertilizers like ammonium sulphate and superphosphate of lime. It is used in the manufacturing of hydrochloric acid, nitric acid, phosphoric acid, ether, plastics and metal sulphates. It is also used in the manufacturing of dyes, drugs, perfumes, disinfectants and glue.
In simple words: Sulphuric acid is crucial in the chemical industry due to its extensive use in producing fertilizers like ammonium sulphate, other important acids like hydrochloric and nitric acid, and various products such as plastics, dyes, drugs, and disinfectants. Its versatility makes it a cornerstone chemical.

🎯 Exam Tip: When describing the importance of a chemical, list specific applications and products it helps create. Emphasize its role in major industrial sectors like agriculture (fertilizers) and manufacturing to demonstrate comprehensive understanding.

Question 4. Give answers.

Question a. Which acid is used for getting chloride salt?
Answer:
Hydrochloric acid is used for getting chloride salt.
In simple words: Hydrochloric acid is used to produce chloride salts because it contains chloride ions which can combine with various metal ions.

🎯 Exam Tip: For questions asking for a specific acid related to a salt type, connect the anion of the salt (e.g., chloride) directly to the corresponding acid (e.g., hydrochloric acid).

Question b. By squeezzing lemon on a piece of rock the gas liberated turned lime water milky. Which compound is present in the rock?
Answer:
Metal carbonate is present in the rock.
In simple words: The effervescence (gas liberation) and subsequent milky lime water when lemon juice is squeezed on a rock indicate the presence of a metal carbonate in the rock, as acids react with carbonates to produce carbon dioxide gas.

🎯 Exam Tip: Remember that the reaction between an acid and a carbonate produces carbon dioxide gas, which turns lime water milky. This is a classic test for carbonates.

Question c. The label on the bottle of chemical is spoiled. How will you find whether the chemical is acidic or not?
Answer:
The chemical is tested with blue litmus paper. If it turns red it is an acidic otherwise tested with red litmus paper, if it turns blue, it is an alkaline.
In simple words: To determine if an unlabeled chemical is acidic, you can use litmus paper: if blue litmus paper turns red, it's an acid; if red litmus paper turns blue, it's an alkali (base).

🎯 Exam Tip: Always describe the full test, including using both blue and red litmus paper, to conclusively identify a solution as acidic, basic, or neutral, as one color change alone might not be sufficient for a complete conclusion.

Question 5. Answer the following questions.

Question a. Explain the difference between acid and base.
Answer:
Acids:
1. Acids have sour taste.
2. Acids turn blue litmus red.
Bases:
1. Bases have bitter taste.
2. Bases turn red litmus blue.
In simple words: Acids generally taste sour and turn blue litmus paper red, while bases (alkalis) generally taste bitter and turn red litmus paper blue. These are basic characteristics used to differentiate them.

🎯 Exam Tip: When differentiating acids and bases, always include both taste (though never taste in a lab!) and their characteristic reactions with litmus paper. Mentioning the release of H+ ions for acids and OH- ions for bases in aqueous solutions would also add value.

Question b. Why indicator does not affect by salt?
Answer:
Mostly indicators are organic compounds which do not react with a salt.
In simple words: Indicators, being organic compounds, typically do not react with neutral salts because salts do not produce significant amounts of H+ or OH- ions in solution to cause a color change.

🎯 Exam Tip: Explain that indicators are sensitive to changes in pH (H+ or OH- concentration). Since neutral salts do not significantly alter pH, indicators typically do not show a color change in their presence.

Question c. Which substances are produced i by neutralization process?
Answer:
Salt and water are produced in the neutralization process.
In simple words: When an acid and a base react in a neutralization process, they always form salt and water as the products.

🎯 Exam Tip: The products of a neutralization reaction are consistently a salt and water. This is a fundamental concept, so remember these two products without fail.

Question d. Which are the industrial uses of acids?
Answer:
Acids which are used in the industry are:
1. Sulphuric acid
2. Hydrochloric acid
3. Nitric acid.
1. Sulphuric acid: Sulphuric acid is used (a) in the manufacture of chemical fertilizers like ammonium sulphate, (b) for cleaning gold and silver articles and (c) in car batteries.
2. Hydrochloric acid: Hydrochloric acid is used (a) to clean toilets and (b) to obtain glucose from starch and also for producing gelatine.
3. Nitric acid: Nitric acid is used (a) in the manufacture of perfumes (b) for engraving on copper, brass or silver and (c) in the manufacture of paints and explosives.
In simple words: Industrially, sulphuric acid is vital for fertilizers, metal cleaning, and car batteries; hydrochloric acid is used for cleaning and producing glucose; and nitric acid is essential for perfumes, metal engraving, paints, and explosives.

🎯 Exam Tip: When listing industrial uses, provide specific examples for each acid rather than general applications. This demonstrates a deeper understanding of their practical importance.

Question 6. Select proper word given in bracket and fill in the blanks.

Question a. Main constituent of acid is ................ .
Answer:
Main constituent of acid is H+ ion.
In simple words: The primary component that makes a substance an acid is the presence of hydrogen ions (H+).

🎯 Exam Tip: Always remember that the defining characteristic of an acid in aqueous solution is its ability to release hydrogen ions (H+).

Question b. Main constituent of alkali is ................ .
Answer:
Main constituent of alkali is OH- ion.
In simple words: The main component that defines an alkali (base) is the presence of hydroxide ions (OH-).

🎯 Exam Tip: For alkalis in aqueous solution, the release of hydroxide ions (OH-) is their characteristic property. Note the negative charge on the hydroxide ion.

Question c. Tartaric acid is a ................ acid.
Answer:
Tartaric acid is a weak acid.
In simple words: Tartaric acid is classified as a weak acid, meaning it does not fully ionize in solution.

🎯 Exam Tip: Distinguish between strong acids (like HCl, H2SO4, HNO3) and weak acids (like tartaric acid, acetic acid, carbonic acid) based on their degree of ionization in water.

Question 7. Match the pairs.

Question a.

🎯 Exam Tip: For 'Match the Pairs' questions, create a mental list of common substances and their associated chemical components. This helps in quickly and accurately linking the items.

Question 8. State true or false.

Question a. Oxides of metals are alkaline in nature.
Answer:
True.
In simple words: The statement is true because when metal oxides dissolve in water, they typically form hydroxides, which are alkaline (basic) solutions.

🎯 Exam Tip: Remember the general rule: metal oxides are basic, and non-metal oxides are acidic (or neutral, in some cases). This distinction is crucial for understanding chemical properties.

Question b. Salt is acidic.
Answer:
False. (Salt is neutral)
In simple words: The statement is false because salts formed from strong acids and strong bases are typically neutral, although salts can also be acidic or basic depending on their parent acid and base.

🎯 Exam Tip: While many common salts are neutral, it's important to clarify that salts can also be acidic or basic depending on the strength of the acid and base from which they are formed. For a general statement like this, "neutral" is the common expectation.

Question c. Metal corrodes due to salts.
Answer:
False. (Acids and bases corrode metals)
In simple words: The statement is false; while some salts can contribute to corrosion, it is primarily acids and bases that directly corrode metals through chemical reactions.

🎯 Exam Tip: Differentiate between the direct corrosive action of acids and bases on metals and the indirect role of salts in accelerating corrosion, often by enhancing conductivity in electrochemical processes.

Question d. Salts are neutral.
Answer:
True. (Not all salts neutral)
In simple words: This statement is generally considered true for salts formed from strong acids and strong bases, resulting in a neutral solution, but it's important to note that not all salts are neutral; some can be acidic or basic.

🎯 Exam Tip: When stating 'True' for a general statement like this, it's good practice to add a clarifying parenthetical remark, like "(Not all salts neutral)," to show a nuanced understanding that exceptions exist based on the parent acid and base strengths.

Question 9. Classify the following substances into acidic, basic and neutral group: HCl, NaCl, MgO, KCl, CaO, H2SO4, HNO3, H2O and Na2CO3.

Question a. Classify the following substances into acidic, basic and neutral group: HCl, NaCl, MgO, KCl, CaO, H2SO4, HNO3, H2O and Na2CO3.
Answer:

🎯 Exam Tip: For classification questions, clearly identify the defining characteristic of each group (e.g., strong acids, metal oxides for bases, common salts and water for neutral) and meticulously place each substance under its correct category.

Project:

Question a. Write in your own language the uses and importance of neutralization reaction in daily life.
Answer:
[Student's own answer demonstrating understanding of neutralization in contexts like antacids for acidity, agriculture for soil pH, wastewater treatment, and pest control.]
In simple words: Neutralization reactions are important in daily life for things like taking antacids to relieve stomach acidity, balancing soil pH in agriculture, treating wastewater, and even in some cleaning products to counteract acidic or basic spills.

🎯 Exam Tip: When answering 'Project' or 'Write in your own language' questions, provide diverse examples from daily life to showcase a broad understanding of the concept's practical applications, explaining how neutralization solves a problem in each scenario.

Class 8 Science Chapter 12 Introduction to Acid and Base Important Questions and Answers

Fill in the blanks:

Question 1. Acid reacts with metal to form ................ gas.
Answer:
Acid reacts with metal to form hydrogen gas.
In simple words: When an acid reacts with most metals, it produces hydrogen gas, often observed as bubbles.

🎯 Exam Tip: Recall the general reaction: Acid + Metal → Salt + Hydrogen gas. This is a fundamental chemical property of acids.

Question 2. DNA is an acid present in our body, it decides ................ properties.
Answer:
DNA is an acid present in our body, it decides heredity properties.
In simple words: DNA, which is a type of acid in our bodies, carries the genetic information that determines our inherited traits.

🎯 Exam Tip: Connect DNA (Deoxyribonucleic acid) to its biological function of carrying genetic information and determining hereditary characteristics. This links chemistry to biology.

Question 3. The chemical formula of milk of magnesia is ................ .
Answer:
The chemical formula of milk of magnesia is Mg(OH)2.
In simple words: Milk of magnesia, a common antacid, has the chemical formula Mg(OH)2, indicating it's magnesium hydroxide.

🎯 Exam Tip: Memorize the chemical formulas of common compounds, especially those mentioned in the textbook, as they are frequently tested in fill-in-the-blanks or matching questions.

Question 4. ................ are used to control hyperacidity.
Answer:
Antacids are used to control hyperacidity.
In simple words: Antacids are medicines used to alleviate excessive stomach acid, known as hyperacidity.

🎯 Exam Tip: Understand that antacids work by neutralizing excess acid in the stomach, hence connecting their function to the concept of neutralization.

Question 5. Alkali has ................ taste.
Answer:
Alkali has bitter taste.
In simple words: Alkalis, also known as bases, are characterized by their bitter taste.

🎯 Exam Tip: While taste is a characteristic property, never taste chemicals in a laboratory setting. This is a descriptive property for identification, but safety comes first.

Question 6. Proteins are made up of ................ .
Answer:
Proteins are made up of amino acids.
In simple words: Proteins are large biological molecules built from smaller units called amino acids, linked together in long chains.

🎯 Exam Tip: Recall the basic building blocks of macromolecules. For proteins, the fundamental units are amino acids. This connects to basic biochemistry.

Question 7. ................ is used in batteries.
Answer:
Dil. H2SO4 is used in batteries.
In simple words: Diluted sulphuric acid (H2SO4) is a key component found in lead-acid batteries, such as those in cars.

🎯 Exam Tip: Identify specific applications for common acids, like the use of dilute sulphuric acid in car batteries (lead-acid batteries), which is a practical application of acid chemistry.

Rewrite the following statements by selecting the correct options:

Question 1. The colour of phenolphthalein indicator in alkaline solution is ................ .
(a) yellow
(b) green
(c) orange
(d) pink
Answer: (d) pink
In simple words: Phenolphthalein indicator turns pink when it is in an alkaline (basic) solution.

🎯 Exam Tip: Memorize the color changes of common indicators in both acidic and basic mediums. Phenolphthalein is colorless in acid and pink in base.

Question 2. ................ is sour to taste.
(a) An acid
(b) An alkali
(c) A salt
(d) Alcohol
Answer: (a) An acid
In simple words: Acids are chemically characterized by having a sour taste.

🎯 Exam Tip: Recall the basic properties of acids and bases. Acids are typically sour, while bases are bitter and slippery.

Question 3. When phenolphthalein is added to NaOH, the colour of the solution will become ................ .
(a) colourless
(b) red
(c) pink
(d) yellow
Answer: (c) pink
In simple words: Since NaOH (sodium hydroxide) is a strong base (alkaline solution), adding phenolphthalein to it will turn the solution pink.

🎯 Exam Tip: Identify NaOH as a strong alkali (base). Then, apply the known color change of phenolphthalein in basic solutions (pink) to determine the answer.

Question 4. When phenolphthalein is added to HCl, the colour of the solution will be ................ .
(a) red
(b) pink
(c) green
(d) colourless
Answer: (d) colourless
In simple words: HCl (hydrochloric acid) is an acid, and phenolphthalein remains colorless in acidic solutions.

🎯 Exam Tip: Recognize HCl as a strong acid. Then, apply the rule that phenolphthalein stays colorless in acidic conditions to determine the result.

Question 5. ................ is a natural indicator.
(a) Phenolphthalein
(b) Methyl orange
(c) Litmus
(d) Methyl red
Answer: (c) Litmus
In simple words: Litmus is a natural indicator derived from lichens, unlike phenolphthalein, methyl orange, and methyl red which are synthetic.

🎯 Exam Tip: Differentiate between natural indicators (like litmus, turmeric, red cabbage juice) and synthetic indicators (like phenolphthalein, methyl orange, methyl red).

Question 6. The litmus paper or the litmus solution is obtained from ................ plants.
(a) moss
(b) rose
(c) hibiscus
(d) lichen
Answer: (d) lichen
In simple words: Litmus, a widely used natural indicator for acids and bases, is extracted from lichens.

🎯 Exam Tip: Know the natural source of litmus paper. This is a specific fact often asked in objective questions.

Question 7. ................ is not an alkali.
(a) Sodium hydroxide
(b) Potassium hydroxide
(c) Copper hydroxide
(d) Calcium hydroxide
Answer: (c) Copper hydroxide
In simple words: Copper hydroxide is generally insoluble in water and thus does not readily form hydroxide ions in solution, making it an insoluble base rather than a soluble alkali. Sodium, potassium, and calcium hydroxides are soluble and thus considered alkalis.

🎯 Exam Tip: Understand that all alkalis are bases, but not all bases are alkalis. Alkalis are bases that are soluble in water. Recognize common soluble hydroxides as alkalis and insoluble hydroxides as just bases.

Question 8. ................ is a weak acid.
(a) Hydrochloric acid
(b) Nitric acid
(c) Carbonic acid
(d) Sulphuric acid
Answer: (c) Carbonic acid
In simple words: Carbonic acid (H2CO3) is considered a weak acid because it only partially dissociates into ions in water, unlike strong acids such as hydrochloric, nitric, and sulphuric acids.

🎯 Exam Tip: Be able to identify common strong acids (HCl, HNO3, H2SO4) and weak acids (e.g., carbonic acid, acetic acid, citric acid). Weak acids dissociate partially in water.

Question 9. When methyl orange is added to HCl, the colour of the solution will be ................ .
(a) red
(b) pink
(c) yellow
(d) colourless
Answer: (b) pink
In simple words: When methyl orange is added to hydrochloric acid (HCl), which is a strong acid, the indicator will turn pink.

🎯 Exam Tip: Remember the color changes for methyl orange: it is red/pink in acidic solutions and yellow in basic solutions. HCl is an acid.

Question 10. When blue litmus paper is added to NaOH, the colour of the litmus paper will be ................ .
(a) blue
(b) red
(c) pink
(d) yellow
Answer: (a) blue
In simple words: Sodium hydroxide (NaOH) is a base, and blue litmus paper remains blue in a basic solution.

🎯 Exam Tip: Recall the litmus paper rules: blue litmus turns red in acid, and red litmus turns blue in base. Blue litmus remains blue in a basic or neutral solution.

State whether the following statements are true or false. If a statement is false, correct it and rewrite:

Question 1. Red cabbage is a natural indicator.
Answer:
True
In simple words: Red cabbage juice can indeed be used as a natural indicator because it changes color depending on the pH of a solution.

🎯 Exam Tip: Be familiar with various natural substances that act as pH indicators, such as red cabbage, turmeric, and hibiscus petals.

Question 2. Fats of our body are formed by fatty acids.
Answer:
True.
In simple words: Fats in our bodies are primarily composed of fatty acids linked to glycerol molecules, forming triglycerides.

🎯 Exam Tip: Understand the basic building blocks of different biomolecules. For fats, fatty acids are the key components.

Question 3. Ammonium hydroxide is used in the production of fertilizers.
Answer:
True.
In simple words: Ammonium hydroxide is utilized in the fertilizer industry as a source of ammonia, which is essential for synthesizing nitrogen-based fertilizers.

🎯 Exam Tip: Connect the chemical properties of ammonium hydroxide (being a source of nitrogen) to its practical application in agriculture as a component in fertilizers.

Question 4. Lime water is a weak acid.
Answer:
False. (Limewater is a weak base)
In simple words: Limewater (calcium hydroxide solution) is actually a weak base, not a weak acid, as it produces hydroxide ions in water.

🎯 Exam Tip: Correctly identify common substances as acids or bases. Limewater, being calcium hydroxide, is a base, and since it is only sparingly soluble, it is considered a weak base.

Question 5. Orange colour of methyl orange turns yellow in acid.
Answer:
False. (Orange colour of methyl orange turns pink in acid)
In simple words: Methyl orange indicator turns pink or red in acidic solutions, not yellow, while it turns yellow in basic solutions.

🎯 Exam Tip: Review the color changes for methyl orange carefully: it is pink/red in acid and yellow in base. This is a common point of confusion.

Question 6. Methyl red turns yellow in alkali.
Answer:
True.
In simple words: Methyl red indicator indeed changes to a yellow color when placed in an alkaline (basic) solution.

🎯 Exam Tip: Familiarize yourself with the specific pH ranges and corresponding color changes for different indicators. Methyl red is typically red in acidic solutions and yellow in basic solutions.

Question 7. Oxalic acid is used in aerated cold drinks.
Answer:
False. (Carbonic acid is used in aerated cold drinks).
In simple words: Carbonic acid, formed from dissolved carbon dioxide, is responsible for the fizz and slight acidity in aerated cold drinks, not oxalic acid.

🎯 Exam Tip: Correctly associate specific acids with their common applications. Carbonic acid (H2CO3) is the acid found in carbonated beverages.

Find the odd one out and justify:

Question 1. Acetic acid, carbonic acid, hydrochloric acid, nitric acid.
Answer:
Acetic acid. (Others are mineral acids.)
In simple words: Acetic acid is the odd one out because it is an organic acid, whereas hydrochloric acid, carbonic acid, and nitric acid are inorganic (mineral) acids.

🎯 Exam Tip: Classify acids into organic (containing carbon, typically from living organisms) and inorganic/mineral acids. This distinction helps in identifying the odd one out.

Question 2. Hydrogen chloride, sodium hydroxide, calcium oxide, ammonia.
Answer:
Hydrogen chloride. (Others are bases.)
In simple words: Hydrogen chloride is the odd one out as it is an acid, while sodium hydroxide, calcium oxide, and ammonia are all bases.

🎯 Exam Tip: Be able to categorize compounds as acids or bases. HCl forms a strong acid, while NaOH, CaO, and NH3 (ammonia, which forms NH4OH in water) are bases.

Question 3. HCl, CH3COOH, H2SO4, HNO3
Answer:
CH3COOH. (Others are strong acids.)
In simple words: CH3COOH (acetic acid) is the odd one out because it is a weak acid, whereas HCl, H2SO4, and HNO3 are all strong acids.

🎯 Exam Tip: Distinguish between strong acids (fully ionize) and weak acids (partially ionize). This is a common way to categorize acids.

Question 4. NaOH, Ca(OH)2, NH4OH, Ba(OH)2
Answer:
NaOH (Others are weak bases.)
In simple words: NaOH (sodium hydroxide) is the odd one out because it is a strong base, while Ca(OH)2 (calcium hydroxide), NH4OH (ammonium hydroxide), and Ba(OH)2 (barium hydroxide) are generally considered weak bases (or sparingly soluble bases).

🎯 Exam Tip: Learn to differentiate between strong bases (Group 1 hydroxides) and weak/sparingly soluble bases (most other metal hydroxides and ammonium hydroxide).

Question 5. H2SO4, H2CO3, HCl, HNO3
Answer:
H2CO3 (Others are strong acids.)
In simple words: H2CO3 (carbonic acid) is the odd one out because it is a weak acid, while H2SO4, HCl, and HNO3 are all strong acids.

🎯 Exam Tip: Reiterate the strong vs. weak acid classification. Carbonic acid is formed from CO2 in water and is a common weak acid.

Question 6. Citric acid, formic acid, lactic acid, nitric acid.
Answer:
Nitric acid. (Others are organic acids.)
In simple words: Nitric acid is the odd one out because it is an inorganic (mineral) acid, whereas citric acid, formic acid, and lactic acid are all organic acids.

🎯 Exam Tip: Remember that organic acids contain carbon and are typically found in living organisms (e.g., fruit acids), while inorganic acids do not have a carbon backbone.

Question 7. Lime, litmus, phenolphthalein, methyl orange.
Answer:
Lime. (Others are indicators.)
In simple words: Lime (calcium oxide or hydroxide) is the odd one out because it is a base, whereas litmus, phenolphthalein, and methyl orange are all substances used as acid-base indicators.

🎯 Exam Tip: Clearly distinguish between a chemical substance that acts as an acid or base (like lime) and a substance that indicates the presence of acids or bases (indicators).

Match the following:

Question 1.

🎯 Exam Tip: For matching questions, systematically go through each item in Column 'A' and find its best corresponding match in Column 'B'. This requires knowing examples for each classification (strong/weak acid/base).

Question 2.

🎯 Exam Tip: When matching uses of substances, think about their characteristic properties (e.g., strong base for soap, mild base for antacid, lime for whitewash) to correctly associate them with their applications.

Define the following:

Question 1. Acid: A substance which gives H+ ions in water is called an acid.
Answer:
Acid: A substance which gives H+ ions in water is called an acid.
\[ \text{HCl(aq)} \implies \text{H}^+ \text{(aq)} + \text{Cl}^- \text{(aq)} \]
In simple words: An acid is defined as a substance that releases hydrogen ions (H+) when dissolved in water.

🎯 Exam Tip: The Arrhenius definition of an acid, focusing on H+ ion release in water, is a fundamental concept. Be prepared to state it and give a simple chemical equation example.

Question 2. Alkali: A substance which gives OH- ions in water is called an alkali.
Answer:
Alkali: A substance which gives OH- ions in water is called an alkali.
\[ \text{NaOH(aq)} \implies \text{Na}^+ \text{(aq)} + \text{OH}^- \text{(aq)} \]
In simple words: An alkali is a base that is soluble in water and releases hydroxide ions (OH-) when it dissolves.

🎯 Exam Tip: The Arrhenius definition of an alkali/base focuses on the release of OH- ions in water. Remember that all alkalis are bases, but not all bases are alkalis (some bases are insoluble).

Define The Following:

Question 1. Acid: A substance which gives H+ ions in water is called an acid.
Answer: \(HCl_{(aq)}\)
\( \implies H^+ + Cl^-\)
In simple words: An acid is a chemical compound that releases hydrogen ions (H+) when dissolved in water, making the solution acidic.

🎯 Exam Tip: Remember to define acids by their ability to donate H+ ions in water and be ready to provide a simple chemical example like HCl dissociation.

Question 2. Alkali: A substance which gives OH- ions in water is called an alkali.
Answer: \(NaOH_{(aq)}\)
\( \implies Na^+_{(aq)} + OH^-\)
In simple words: An alkali is a base that is soluble in water and produces hydroxide ions (OH-) when dissolved, leading to a basic solution.

🎯 Exam Tip: Focus on the characteristic of alkalis releasing OH- ions in aqueous solutions and use strong alkali examples like NaOH for your answer.

Question 3. Indicator: Substances which change their colours in presence of acid or base are called indicators.
Answer: Substances which change their colours in presence of acid or base are called indicators.
In simple words: Indicators are special chemicals that change color when they come into contact with an acid or a base, helping us identify the nature of a solution.

🎯 Exam Tip: When defining indicators, emphasize their color-changing property in the presence of acids or bases, as this is their primary function.

Question 4. Neutralization: The reaction between an acid and an alkali to form the r salt and water is termed as neutralization.
Answer: The reaction between an acid and an alkali to form the salt and water is termed as neutralization.
In simple words: Neutralization is a chemical reaction where an acid and a base combine to form a salt and water, effectively canceling out each other's properties.

🎯 Exam Tip: For neutralization, clearly state that it involves an acid and an alkali reacting to produce salt and water, which is a fundamental concept in chemistry.

Answer The Following Questions In One Sentence Each:

Question 1. What are natural acids?
Answer: Acids present in foodstuffs are called natural acids.
In simple words: Natural acids are organic acids found naturally in food items like fruits and vegetables.

🎯 Exam Tip: Keep your answer concise by linking natural acids directly to their presence in foodstuffs.

Question 2. State three vegetables from which natural indicators can be prepared.
Answer: Natural indicators: Red cabbage, radish, tomato.
In simple words: Red cabbage, radish, and tomato are common vegetables that can be used to make natural acid-base indicators.

🎯 Exam Tip: List at least two or three common examples of vegetables used as natural indicators to ensure full marks.

Question 3. State names of any three strong acids.
Answer:
1. Hydrochloric acid
2. Sulphuric acid
3. Nitric acid.
In simple words: Hydrochloric acid, Sulphuric acid, and Nitric acid are examples of very strong acids that dissociate completely in water.

🎯 Exam Tip: Memorize the names of the three most common strong acids: Hydrochloric, Sulphuric, and Nitric acid.

Question 4. State the names of the acids found in lemon juice, Amla, tamarind water and curd.
Answer:
1. Lemon juice - citric acid
2. Amla - ascorbic acid
3. Tamarind water - tartaric acid
4. Curd - lactic acid.
In simple words: Different natural acids like citric acid in lemon, ascorbic acid in Amla, tartaric acid in tamarind, and lactic acid in curd are responsible for their sour tastes.

🎯 Exam Tip: Practice associating common food items with the specific natural acids they contain; this is a frequent knowledge-based question.

Question 5. State names of any three alkalis.
Answer:
1. Sodium hydroxide
2. Potassium hydroxide
3. Calcium hydroxide.
In simple words: Sodium hydroxide, Potassium hydroxide, and Calcium hydroxide are common examples of alkalis, which are soluble bases.

🎯 Exam Tip: Be ready to name at least three common alkalis, such as sodium hydroxide, potassium hydroxide, and calcium hydroxide.

Question 6. State the names of three indicators.
Answer:
1. Litmus paper
2. Methyl orange
3. Phenolphthalein.
In simple words: Litmus paper, Methyl orange, and Phenolphthalein are three commonly used indicators for detecting acids and bases.

🎯 Exam Tip: Know the names of at least three indicators and ideally their color changes in acidic and basic mediums.

Question 7. State the names of three weak alkalis.
Answer:
1. Calcium hydroxide
2. Ammonium hydroxide
3. Magnesium hydroxide.
In simple words: Calcium hydroxide, Ammonium hydroxide, and Magnesium hydroxide are examples of weak alkalis that do not fully dissociate in water.

🎯 Exam Tip: Differentiate between strong and weak alkalis and be able to provide examples for both categories.

Question 8. From which plant is litmus obtained?
Answer: Litmus is obtained from plants called lichens.
In simple words: Litmus, a natural indicator, is extracted from organisms known as lichens.

🎯 Exam Tip: Remember that litmus, a key indicator, originates from lichens.

Question 9. Name the antacid which is used to control the hyper acidity.
Answer: Milk of magnesia [Mg(OH)2] is used to control the hyper acidity.
In simple words: Milk of magnesia, containing magnesium hydroxide, is an antacid commonly used to relieve hyperacidity.

🎯 Exam Tip: Connect hyperacidity relief with Milk of Magnesia and its active ingredient, magnesium hydroxide.

Question 10. How will you neutralize the excess of acid present in the soil?
Answer: Lime stone or lime water is mixed in the soil to neutralize the excess of acid.
In simple words: To reduce soil acidity, farmers add alkaline substances like limestone or lime water to balance the pH.

🎯 Exam Tip: Note that alkaline substances like limestone or limewater are used to neutralize acidic soil, demonstrating practical application of neutralization.

Question 11. When lemon juice falls on a marble kitchen counter, which is the gas that bubbled out?
Answer: Carbon dioxide.
In simple words: When acidic lemon juice reacts with the calcium carbonate in marble, carbon dioxide gas is produced, causing bubbles.

🎯 Exam Tip: This question highlights the reaction of an acid with a carbonate, which always produces carbon dioxide gas and is a common observation in everyday life.

Answer The Following Questions:

Question 1. What are indicators?
Answer: Substances which change their colours in presence of acid or base are called indicators.
In simple words: Indicators are special chemicals that change color when they come into contact with an acid or a base, helping us identify the nature of a solution.

🎯 Exam Tip: When defining indicators, emphasize their color-changing property in the presence of acids or bases, as this is their primary function.

Question 2. State two acid-base indicators and mention their colour change.
Answer: Phenolphthalein and methyl orange are two acid-base indicators. Phenolphthalein is colourless in an acidic solution while it turns pink in a basic solution. Methyl orange gives orange colour with an acidic solution and yellow colour with a basic solution.
In simple words: Phenolphthalein is clear in acid and pink in base, while methyl orange is orange in acid and yellow in base; both are used to detect acidity or alkalinity.

🎯 Exam Tip: For this type of question, ensure you name two indicators and accurately describe their distinct color changes in both acidic and basic environments.

Question 3. State the colour change for each of the following solutions with red litmus, blue litmus, phenolphthalein and methyl orange solutions.
Answer:

🎯 Exam Tip: Create a mental or actual table to organize the color changes of different indicators with various acids and bases for easy recall during exams.

Question 4. Name the acid present in (1) Orange (2) Vinegar (3) Tamarind (4) Curd (5) Tomato (6) Lemon.
Answer:

🎯 Exam Tip: This question tests your knowledge of natural acids found in common food items; memorize the specific acid for each substance listed.

Question 5. Classify the following into acidic substances, basic substances and salts.
(1) Lime water, (2) soda water, (3) soap water, (4) sea water, (5) sweet lime juice, (6) sugar cane juice, (7) buttermilk, (8) a mixture of ash in water, (9) tamarind water.
Answer:
a. Acidic substances: (1) Soda water, (2) sweet lime juice, (3) buttermilk, (4) tamarind water.
b. Basic substances: (1) Lime water, (2) Soap water, (3) a mixture of ash in water.
c. Salts: (1) Sea water, (2) sugar cane juice.
In simple words: We can categorize these substances: soda water, sweet lime juice, buttermilk, and tamarind water are acidic; lime water, soap water, and ash in water are basic; and sea water and sugar cane juice are salts (or neutral solutions).

🎯 Exam Tip: Understand the general properties of acids, bases, and salts (or neutral substances) to classify common household items correctly.

Question 6. What happens when sour substances like lime juice, tamarind water falls on shahabad stones or kitchen platform? Why?
Answer: When sour substances like lime juice, tamarind water falls on shahabad stones or kitchen platform, citric acid present in lime juice and tartaric acid in tamarind water reacts with metal carbonates present in shahabad stones or kitchen platform, carbon dioxide gas is evolved resulting in the formation of uneven surface.
In simple words: Sour substances like lemon juice or tamarind water contain acids that react with the calcium carbonate in stones, producing carbon dioxide gas and causing erosion or an uneven surface.

🎯 Exam Tip: This question demonstrates an acid-carbonate reaction; remember that acids react with carbonates to produce carbon dioxide, which can cause damage to surfaces like marble.

Question 7. Collect soil samples from your surroundings and find out whether it is acidic or alkaline or neutral?
Answer: Soil samples collected from the surroundings are acidic in nature.
In simple words: The soil samples from the local area were tested and found to be acidic.

🎯 Exam Tip: For practical-based questions like this, state your observation clearly and directly.

Question 8. Which substances are used to clean greenish stains on copper vessels and to shine blackish silver utensils?
Answer: Tamarind pulp is used to clean greenish stains on copper vessels. To shine blackish silver utensils, ammoniacal solution or lime juice or detergent is used.
In simple words: Tamarind pulp cleans green copper stains, while ammoniacal solution, lime juice, or detergent are used to shine tarnished silver.

🎯 Exam Tip: This question highlights practical applications of acids and bases in cleaning; know that acids like those in tamarind clean copper, and mild bases/acids can polish silver.

Question 9. Why toothpaste is used for brushing teeth?
Answer:
1. Toothpaste contains fluorides and alkali to neutralize the mouth acid.
2. Hence, the tooth paste, which is generally alkaline, is used for cleaning the teeth as it can neutralize the excess acid in the mouth and prevent tooth decay.
In simple words: Toothpaste is used to brush teeth because its alkaline nature helps neutralize the acids produced in the mouth, which are responsible for tooth decay.

🎯 Exam Tip: Explain the role of toothpaste in neutralizing mouth acids to prevent tooth decay, focusing on its alkaline properties.

Question 10. State the properties of acids.
Answer:
1. Acids are sour in taste.
2. Acid molecules contain hydrogen ion (H+) as a main constituent.
3. Acid reacts with metal to form hydrogen gas.
4. Acid reacts with carbonates and liberates \(CO_2\) gas.
5. Blue litmus turns red in acid.
In simple words: Acids taste sour, contain H+ ions, react with metals to produce hydrogen gas, react with carbonates to release carbon dioxide, and turn blue litmus paper red.

🎯 Exam Tip: List at least three to four distinct properties of acids, including taste, ion presence, reactivity with metals/carbonates, and litmus test, for a complete answer.

Question 11. State the uses of acids.
Answer:
1. Acids are used in the production of chemical fertilizers.
2. Acids are used in the production of explosives, oil purification, medicines, dyes and paints.
3. Hydrochloric acid is used for the preparation of different types of chloride salts.
4. Dil. \(H_2SO_4\) acid is used in the batteries (electric cell).
5. Dil. HCl is used for sterilization of water.
6. Acid is used for making of white paper from wood pulp.
In simple words: Acids are widely used in making fertilizers, explosives, medicines, dyes, paints, and chloride salts, and dilute versions are used in batteries, water sterilization, and paper production.

🎯 Exam Tip: Provide diverse examples of acid uses across various industries and applications, demonstrating their importance beyond the laboratory.

Question 12. The iron knife shines better after cutting the sour fruits like lemon, raw mangoes. Why?
Answer: Acids present in sour fruits clean and dissolves the salts present on the surface of iron knife as a result iron knife shines better after cutting the sour fruits.
In simple words: The acids in sour fruits dissolve and remove the dull salt or oxide layer from the iron knife's surface, making it appear shinier.

🎯 Exam Tip: Explain that acids react with and remove the dull layer (salts/oxides) on metals, leading to a shiny appearance, which is a common cleaning principle.

Question 13. What is meant by neutralization? Give example.
Answer: When an acid reacts with an alkali to form a salt and water, it is called neutralization.
Acid + Base \(\implies\) Salt + Water
\(HCl\) + \(NaOH\)
\( \implies NaCl + H_2O\)
In simple words: Neutralization is a chemical reaction where an acid and a base combine to form a salt and water, cancelling out each other's properties, like hydrochloric acid and sodium hydroxide forming salt and water.

🎯 Exam Tip: Provide both a clear definition and a balanced chemical equation example (like HCl + NaOH) to illustrate the concept of neutralization completely.

Give Scientific Reasons:

Question 1. When we have stomachache, doctors prescribe medicine containing magnesium hydroxide.
Answer:
1. There is hydrochloric acid in our stomach which helps in the digestion of food.
2. Sometimes in the stomach, there is more hydrochloric acid than we need.
3. This excess acid causes acidity and indigestion resulting in stomachache.
4. When magnesium hydroxide is administered it neutralizes the extra acid in the stomach.
5. Therefore, magnesium hydroxide is the best cure for stomachache.
6. So, when we have stomachache, doctors prescribe medicine containing magnesium hydroxide.
In simple words: Doctors prescribe magnesium hydroxide for stomachaches because it's an alkali that neutralizes the excess hydrochloric acid in the stomach, alleviating acidity and indigestion.

🎯 Exam Tip: Explain the role of stomach acid, how excess acid causes discomfort, and how magnesium hydroxide (a base) neutralizes it, providing a complete scientific reason.

Question 2. Quicklime or slaked lime is added to the soil.
Answer:
1. When chemical fertilizers are added to the soil, the soil becomes acidic.
2. To reduce its acidity quicklime or slaked lime is added to the soil.
In simple words: Quicklime or slaked lime is added to soil to neutralize acidity caused by chemical fertilizers, optimizing soil pH for plant growth.

🎯 Exam Tip: Focus on how chemical fertilizers can make soil acidic and the role of quicklime/slaked lime as a basic substance to neutralize this acidity.

Question 3. Tarnished and stained copper vessels are brought to a shine by using tamarind pulp.
Answer: In due course, copper vessels are covered with a coating of black copper oxide and other compounds of copper which tarnish the vessel. Tamarind contains tartaric acid. When the vessel is rubbed with tamarind pulp, tartaric acid reacts with copper oxide and removes the layer. Thus, the copper vessel regains its shine.
In simple words: Tamarind pulp shines tarnished copper vessels because its tartaric acid reacts with and removes the black copper oxide layer, restoring the copper's original luster.

🎯 Exam Tip: Highlight the chemical reaction between tartaric acid (in tamarind) and copper oxide (tarnish) as the mechanism for cleaning copper vessels.

Question 4. Copper and brass utensils are tinned.
Answer: Copper and brass reacts with organic acids present in food materials and poisonous salts are formed. Tin does not react with organic acids present in food materials. Therefore, copper or brass vessels are tinned.
In simple words: Copper and brass utensils are tinned to prevent them from reacting with food acids and forming harmful compounds, as tin is non-reactive with these acids.

🎯 Exam Tip: The key reason for tinning copper and brass utensils is to prevent the formation of poisonous compounds due to the reaction of these metals with organic acids in food.

Distinguish Between Acid And Alkali. OR Distinguish Between The Following:

Question 1. Acid and Alkali:
Answer:

🎯 Exam Tip: For distinctions, present contrasting points clearly in a table format, covering taste, litmus test, ion release, and oxide formation.

Activity-Based Questions:

Activity 1:

Apparatus: Hibiscus, rose, turmeric, red cabbage leaves, filter paper, etc.
Activity: Rub red petals of hibiscus flower on the white filter paper. This gives hibiscus indicator paper. Similarly rub, rose petals on the white filter paper. Cut strips of this paper, it is a rose indicator paper. Take turmeric powder, add a little water in it. Dip filter paper or ordinary paper in the turmeric water for some time.
After drying make strips of that paper. Prepare turmeric indicator paper in this way. Put leaves of red cabbage in small quantity of water and heat it. Once solution of cabbage leaves cool down, dip papers in it and dry it. Make strips of dried paper. In this way prepare red cabbage indicator paper. Put some drops of following substances on the indicator papers prepared by the above method and write the effect in the following table:

Activity 2:

Take baking powder. Add a little water to it. Add this solution on to lime juice, vinegar, orange juice, apple juice, etc. and note the findings.
What do you observe on addition of baking soda solution in the fruit juice? Whether bubbles formed or effervescence came out of fruit juice?
From the above first activity we came to know that yellow turmeric indicator paper's turns red in certain solutions. Similarly on addition of baking soda solution in the acidic solution bubbles come out or effervescence is produced.
By these simple and easy activity we can identify acidic or alkaline substance:
[Note for Activity 1 and Activity 2: Students should perform the experiments under the guidance of school teachers and record their observations.]

Activity 3:

Under the guidance of teacher take lime juice, ammonium hydroxide (\(NH_4OH\)), dil. hydrochloric acid (dil. HCl) and nitric acid (\(HNO_3\)) in different test-tubes. Add drops of following indicators in them. Also dip litmus papers in the solutions. Observe and record in the following table.