CBSE Class 10 Science Acids Bases and Salts Assignment Set 02

Question. Which one of the following can be used as an acid– base indicator by a visually impaired student?
(A) Litmus
(B) Turmeric
(C) Vanilla essence
(D) Petunia leaves
Answer : C

Question. What is formed when zinc reacts with sodium hydroxide?
(a) Zinc hydroxide and sodium
(b) Sodium zincate and hydrogen gas
(c) Sodium zinc-oxide and hydrogen gas
(d) Sodium zincate and water
Answer : B

Question. Which of the following statement is correct about an aqueous solution of an acid and of a base?
(i) Higher the pH, stronger the acid
(ii) Higher the pH weaker the acid
(iii ) Lower the pH ,stronger the base
(iv) Lower the pH, weaker the base
(a) i & iii
(b) ii & iii
(c ) I & iv
(d) ii & iv
Answer : D

Question. Tooth enamel is made up of
(a) calcium phosphate
(b) calcium carbonate
(c) calcium oxide
(d) potassium sulphate
Answer : A

Question. Sodium hydroxide turns phenolphthalein solution
(a) pink
(b) yellow
(c) colourless
(d) orange
Answer : A

Question. Which one of the given is true, if a substance has a pH value of 7?
(a) The substance is a base
(b) The substance is an acid
(c) The substance is a neutral substance
(d) Either (A) or (B)
Answer : C

Question. An aqueous solution turns red litmus solution blue. Excess addition of which of the following solution would reverse the change?
(a) Baking powder
(b) Lime
(c) Ammonium hydroxide solution
(d) Hydrochloric acid
Answer : D

Question. Rain is called acid rain when its:
(a) pH falls below 7
(b) pH falls below 6
(c) pH falls below 5.6
(d) pH is above 7
Answer : C

Question. When copper oxide and dilute hydrochloric acid react, colour changes to
(a) white
(b) bluish-green
(c) blue-black
(d) black
Answer : B

Question. Generally, when certain metals react with an acid they release gas.
(a) Nitrogen
(b) Oxygen
(c) Hydrogen
d) Argon
Answer : C

 

 

 

 

ACID, BASES AND SALTS

FORMATIVE ASSESSMENT I - Q.PAPER

Question ii. Name the gas formed when sodium hydroxide reacts with zinc.
Answer: Hydrogen gas (\(\text{H}_2\)) is formed when sodium hydroxide reacts with zinc metal, along with sodium zincate.
In simple words: When zinc reacts with a strong base like sodium hydroxide, it releases hydrogen gas.

Exam Tip: Remember the balanced reaction: \(\text{Zn} + 2\text{NaOH} \rightarrow \text{Na}_2\text{ZnO}_2 + \text{H}_2 \uparrow\).

Question iii. Write the chemical name of baking soda.
Answer: Sodium hydrogen carbonate (or Sodium bicarbonate), with the chemical formula \(\text{NaHCO}_3\).
In simple words: Baking soda is chemically known as sodium bicarbonate.

Exam Tip: Do not confuse baking soda (\(\text{NaHCO}_3\)) with washing soda (\(\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}\)).

Question iiii. What happens when gypsum is heated at 373K?
Answer: When gypsum is heated at 373K (\(100^\circ\text{C}\)), it loses water molecules and becomes Plaster of Paris (Calcium sulfate hemihydrate).
\(\text{CaSO}_4 \cdot 2\text{H}_2\text{O} \xrightarrow{373\text{K}} \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} + 1\frac{1}{2}\text{H}_2\text{O}\)
In simple words: Heating gypsum removes most of its water of crystallization to form Plaster of Paris.

Exam Tip: Note the fractional water molecule in Plaster of Paris (\(\frac{1}{2}\text{H}_2\text{O}\)), which represents two formula units sharing one water molecule.

Question iiv. Which has a higher pH value 1M HCl or 1M NaOH solution?
Answer: 1M NaOH solution has a higher pH value (\(\text{pH} = 14\)) compared to 1M HCl (\(\text{pH} = 0\)).
In simple words: Strong bases like NaOH have high pH values, while strong acids like HCl have very low pH values.

Exam Tip: Higher pH means higher basicity and lower hydrogen ion concentration.

Question iv. Hydrogen ion concentration of an acid is \(1 \times 10^{-2}\) mol/l. What is its pH?
Answer: Given \([\text{H}^+] = 1 \times 10^{-2}\) mol/L.
Using the formula: \(\text{pH} = -\log[\text{H}^+]\)
\(\text{pH} = -\log(10^{-2}) = 2\)
In simple words: The pH is 2, which indicates a strong acidic solution.

Exam Tip: For any acid with \([\text{H}^+] = 1 \times 10^{-n}\), the pH is simply \(n\).

Question ivi. What is meant by 'Water of Crystallisation' of a substance? Describe an activity to show that.
Answer: Water of crystallization is the fixed number of water molecules chemically bound in one formula unit of a salt in its crystalline form.
Activity:
1. Take a few crystals of copper sulfate (\(\text{CuSO}_4 \cdot 5\text{H}_2\text{O}\)) in a dry boiling tube and heat it.
2. Observe that the blue crystals turn white, and water droplets appear on the inner walls of the tube.
3. Add 2-3 drops of water to the cooled white sample; the blue color reappears.
In simple words: It is the water trapped inside crystals that gives them their shape and color, which can be removed by heating.

Exam Tip: Always mention the color change from blue to white upon heating hydrated copper sulfate.

Question ivii. Why does tooth decay start when the pH of mouth is lower than 5.5?
Answer: Tooth enamel is made of calcium hydroxyapatite (a crystalline form of calcium phosphate), which is the hardest substance in the body. When the mouth pH falls below 5.5 due to acid production by bacteria breaking down sugar, the acidic environment corrodes and dissolves the enamel.
In simple words: Acidic conditions in the mouth dissolve the protective enamel coating on teeth, causing cavities.

Exam Tip: Mention tooth enamel composition (calcium phosphate) for full marks.

Question iviii. What is baking powder? How does it make the cake soft and spongy?
Answer: Baking powder is a mixture of baking soda (sodium hydrogen carbonate) and a mild edible acid such as tartaric acid. When mixed with water or heated during baking, the following reaction occurs:
\(\text{NaHCO}_3 + \text{H}^+ \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{Sodium salt of acid}\)
The carbon dioxide (\(\text{CO}_2\)) gas produced gets trapped in the wet dough and escapes slowly, making cakes and breads rise, causing them to become soft and spongy.
In simple words: Baking powder releases carbon dioxide gas when heated, which puffs up the batter to make it spongy.

Exam Tip: Distinguish between baking soda (pure \(\text{NaHCO}_3\)) and baking powder (mixture with an acid).

Question iix. Give Arrhenius definition of an acid and a base. Choose strong acid and strong base from the following: \(\text{CH}_3\text{COOH}, \text{NH}_4\text{OH}, \text{KOH}, \text{HCl}\)
Answer:
- Arrhenius Acid: A substance that dissociates in water to yield hydrogen ions (\(\text{H}^+\)).
- Arrhenius Base: A substance that dissociates in water to yield hydroxide ions (\(\text{OH}^-\)).
- Strong Acid: \(\text{HCl}\)
- Strong Base: \(\text{KOH}\)
In simple words: Acids give hydrogen ions in water, and bases give hydroxide ions. Hydrochloric acid is the strong acid, and potassium hydroxide is the strong base.

Exam Tip: \(\text{CH}_3\text{COOH}\) is a weak acid and \(\text{NH}_4\text{OH}\) is a weak base.

Question ix. What happens when nitric acid is added to egg shell? Give the chemical equation.
Answer: Egg shells are made of calcium carbonate (\(\text{CaCO}_3\)). When nitric acid is added, it reacts to produce calcium nitrate, carbon dioxide gas (which causes effervescence), and water.
\(\text{CaCO}_3 + 2\text{HNO}_3 \rightarrow \text{Ca(NO}_3)_2 + \text{CO}_2 \uparrow + \text{H}_2\text{O}\)
In simple words: Nitric acid dissolves calcium carbonate in egg shells and produces bubbling carbon dioxide gas.

Exam Tip: Always indicate gas evolution using the upward arrow (\(\uparrow\)).

Question ixi. A student prepared solutions of an acid and a base in two separate beakers. She forgot to label the solutions and litmus paper is not available in the laboratory. Since both the solutions are colourless, how will she distinguish between the two?
Answer: She can use another olfactory indicator or a synthetic indicator available in the lab, such as phenolphthalein or methyl orange:
1. Add a few drops of phenolphthalein to both beakers. The solution that turns pink is basic, while the solution that remains colorless is acidic.
2. Alternatively, add a few pieces of zinc metal to both; the one that evolves hydrogen gas bubbles is the acid.
In simple words: Use phenolphthalein indicator-it turns pink in a base and stays colorless in an acid.

Exam Tip: Mentioning phenolphthalein or methyl orange test is the standard laboratory method.

Question ixii. Identify the compound 'X' on the basis of the reactions given below. Write the names and chemical formulae of A, B, C
Compound X + Zn \(\rightarrow\) (A) + \(\text{H}_2\text{(g)}\)
Compound X + HCl \(\rightarrow\) (B) + \(\text{H}_2\text{O}\)
Compound X + \(\text{CH}_3\text{COOH} \rightarrow\) (C) + \(\text{H}_2\text{O}\)
Answer:
- Compound X is Sodium Hydroxide (\(\text{NaOH}\)).
- (A) Sodium zincate, Formula: \(\text{Na}_2\text{ZnO}_2\)
- (B) Sodium chloride, Formula: \(\text{NaCl}\)
- (C) Sodium acetate, Formula: \(\text{CH}_3\text{COONa}\)
In simple words: Compound X is a strong base (NaOH) which reacts with metals to form salts and hydrogen, and with acids to form salt and water.

Exam Tip: Bases react with acids to form salt and water, and with active metals like zinc to form a metal salt and hydrogen gas.

Question ixiii. How is plaster of Paris prepared? What is its chemical formula? Write is chemical name.
Answer:
- Preparation: Plaster of Paris is prepared by heating gypsum (\(\text{CaSO}_4 \cdot 2\text{H}_2\text{O}\)) at \(373\text{K}\).
- Chemical Name: Calcium sulfate hemihydrate.
- Chemical Formula: \(\text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O}\)
In simple words: Plaster of Paris is made by heating gypsum to drive off three-fourths of its water content.

Exam Tip: Ensure the fraction in the formula is written correctly as \(\frac{1}{2}\text{H}_2\text{O}\).

Question ixiv. a) Define strong acid and weak acid.
Answer:
- Strong Acid: An acid that dissociates completely or almost completely in water, producing a high concentration of hydrogen ions (\(\text{H}^+\)), e.g., \(\text{HCl}\).
- Weak Acid: An acid that dissociates only partially in aqueous solution, producing a low concentration of hydrogen ions, e.g., \(\text{CH}_3\text{COOH}\).
In simple words: Strong acids release many hydrogen ions because they break apart completely, whereas weak acids break apart only slightly.

Exam Tip: Use the degree of dissociation as the key defining factor.

Question ixiv. b) A student working in the laboratory added some water to a syrupy liquid taken in tube. The tube immediately cracked and the liquid escaped out, that produced blisters on the skin of the student. Why?
Answer: The syrupy liquid was concentrated sulfuric acid (\(\text{H}_2\text{SO}_4\)). Adding water to concentrated acid is a highly exothermic process. The localized heat generated boils the water instantly, causing the glass tube to crack and hot acid droplets to splatter and burn the skin.
In simple words: Mixing water into concentrated acid releases intense heat that shatters glassware and splashes corrosive acid onto the skin.

Exam Tip: Always remember the laboratory safety rule: "Always add acid to water slowly with constant stirring, never water to acid."

HOTS QUESTIONS

Question Q.1. In one of the industrial process used for manufacture of sodium hydroxide, a gas 'X' is formed as by-product. The gas 'X' reacts with lime water to give a compound 'Y' which is used as a bleaching agent in chemical industry. Identify 'X' and 'Y' giving the chemical equation of the reaction.
Answer:
- Gas 'X' is Chlorine gas (\(\text{Cl}_2\)).
- Compound 'Y' is Bleaching powder (Calcium oxychloride, \(\text{CaOCl}_2\)).
Chemical Equations:
Chlor-alkali process: \(2\text{NaCl (aq)} + 2\text{H}_2\text{O (l)} \rightarrow 2\text{NaOH (aq)} + \text{Cl}_2\text{ (g)} + \text{H}_2\text{ (g)}\)
Reaction with lime water: \(\text{Ca(OH)}_2 + \text{Cl}_2 \rightarrow \text{CaOCl}_2 + \text{H}_2\text{O}\)
In simple words: Electrolysis of brine produces chlorine gas, which reacts with lime water to make bleaching powder.

Exam Tip: Clearly label X and Y before writing the chemical reactions.

Question Q.2. Dry hydrogen chloride gas does not turn blue litmus, whereas hydrochloric acid does. Why?
Answer: Hydrogen chloride gas (\(\text{HCl}\)) does not contain ions in its dry gaseous state and cannot release \(\text{H}^+\) ions. When dissolved in water, it ionizes to form hydronium ions (\(\text{H}_3\text{O}^+\) or \(\text{H}^+\)), which exhibit acidic properties.
\(\text{HCl} + \text{H}_2\text{O} \rightarrow \text{H}_3\text{O}^+ + \text{Cl}^-\)
In simple words: Water is required for HCl to release hydrogen ions and show acidic behavior.

Exam Tip: Emphasize that acid character is due to the presence of aqueous hydrogen ions.

Question Q.3. Acid when react with metals release hydrogen gas but there is one acid which when reacts with metals does not release hydrogen except for two metals. Prove this statement.
Answer: Nitric acid (\(\text{HNO}_3\)) is a strong oxidizing agent. When it reacts with most metals, it oxidizes the hydrogen gas produced into water and gets reduced to nitrogen oxides (\(\text{NO}_2, \text{NO}\)). However, very dilute nitric acid reacts with Magnesium (\(\text{Mg}\)) and Manganese (\(\text{Mn}\)) to evolve hydrogen gas.
\(\text{Mg} + 2\text{HNO}_3 \text{ (dilute)} \rightarrow \text{Mg(NO}_3)_2 + \text{H}_2 \uparrow\)
In simple words: Nitric acid usually oxidizes hydrogen to water instead of releasing it, except with magnesium and manganese.

Exam Tip: Remember Mg and Mn as the two exception metals for nitric acid.

Question Q.4. Name the properties responsible for the following uses of baking powder: (i) Baking industry (ii) As an antacid (iii) As soda-acid fire extinguisher.
Answer:
(i) Baking industry: It releases carbon dioxide gas upon heating, making cakes and dough light and spongy.
(ii) As an antacid: It is mildly basic in nature, which neutralizes excess acid in the stomach.
(iii) As soda-acid fire extinguisher: It reacts with sulfuric acid to rapidly evolve carbon dioxide gas, which cuts off oxygen supply and puts out fires.
In simple words: Baking powder is used for producing carbon dioxide gas and neutralizing acids.

Exam Tip: Link each application directly to the chemical property (gas evolution or neutralization).

Question Q.5. What is meant by water of crystallisation of a substance? What is its importance?
Answer: Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt. It imparts crystalline shape and color to many salts (e.g., blue color of copper sulfate crystals). When heated, crystals lose this water and often lose their color and crystalline structure.
In simple words: It is the bound water that gives crystals their specific geometric form and properties.

Exam Tip: Mention both the structural and color importance of water of crystallization.

Question Q.6. What effect does an increase in concentration of \(\text{H}^+\) ions in a solution have on the pH of a solution?
Answer: An increase in the concentration of hydrogen ions (\(\text{H}^+\)) decreases the pH of the solution, making it more acidic.
In simple words: Higher hydrogen ion concentration results in a lower pH value.

Exam Tip: pH is inversely proportional to hydrogen ion concentration (\(\text{pH} = -\log[\text{H}^+]\)).

Question Q.7. Fresh milk has a pH of 6. When it changes to curd, will its pH value increase or decrease? Why?
Answer: The pH value will decrease. Curd is formed due to the action of bacteria that convert lactose into lactic acid, increasing the concentration of hydrogen ions and lowering the pH.
In simple words: Milk becomes acidic when it turns into curd, causing the pH to drop below 6.

Exam Tip: Acids have a lower pH, so formation of lactic acid decreases pH.

Question Q.8. How does the flow of acid rain water into a river make the survival of aquatic life in a river difficult?
Answer: Acid rain lowers the pH of river water. Most aquatic organisms have a narrow optimal pH survival range. Highly acidic water disrupts their metabolic processes, impairs gill function, and can release toxic heavy metals into the water, making survival difficult.
In simple words: Acid rain makes river water too acidic for fish and aquatic plants to survive.

Exam Tip: Mention the drop in water pH as the primary reason for aquatic toxicity.

Question Q.9. Arrange in the increasing order of their pH values: NaOH solution, Blood, Lemon juice.
Answer: Lemon juice (\(\text{pH} \approx 2.2\) - acidic) < Blood (\(\text{pH} \approx 7.4\) - slightly basic) < NaOH solution (\(\text{pH} \approx 14\) - strongly basic).
Increasing order: Lemon juice < Blood < NaOH solution.
In simple words: Ordered from most acidic to most basic: Lemon juice, Blood, NaOH solution.

Exam Tip: Recall standard pH ranges: acids are below 7, blood is slightly above 7, and strong alkalis are near 14.

Question Q.10. Two solutions A and B have pH values of 5 and 8 respectively. Which solution will be basic in nature?
Answer: Solution B with a pH of 8 will be basic in nature (since pH > 7). Solution A with pH 5 is acidic.
In simple words: Solution B is basic because its pH is greater than 7.

Exam Tip: pH range 0-7 is acidic, 7 is neutral, and 7-14 is basic.

Question Q.11. Why does an aqueous solution of acid conduct electricity?
Answer: An aqueous solution of an acid conducts electricity because acids dissociate in water to produce free hydrogen ions (\(\text{H}^+\) or \(\text{H}_3\text{O}^+\)) and anions, which act as mobile charge carriers.
In simple words: Acids release mobile ions in water that carry electric current.

Exam Tip: Presence of mobile ions is essential for electrical conductivity in solutions.

Question Q.12. How is alkali different from a base?
Answer: An alkali is a water-soluble base. Therefore, all alkalis are bases, but not all bases are alkalis (since many metal oxides and hydroxides are insoluble in water).
In simple words: Alkalis are bases that dissolve completely in water.

Exam Tip: Remember the classic distinction: "All alkalis are bases, but all bases are not alkalis."

FA II - ACIDS, BASES AND SALTS - ORAL QUESTIONS (Conversation Type)

Question 1. a) Acids are sour in taste. Is it a way to find whether a substance is an acid or a base?
Answer: No, tasting unknown laboratory chemicals is extremely dangerous and unsafe because many acids and bases are corrosive and toxic.
In simple words: Never taste laboratory chemicals as they can burn or poison you.

Exam Tip: Always use indicators instead of taste for testing acids and bases.

Question 1. b) What is other physical test?
Answer: Using indicators such as litmus paper, phenolphthalein, or methyl orange to observe color changes.
In simple words: Use chemical indicators to test acidity and basicity safely.

Exam Tip: Indicators provide safe color-based identification.

Question 1. c) Any test with solid acid?
Answer: Solid dry acids generally do not change dry litmus paper color because moisture is required to release hydrogen ions. Dissolving the solid in water or using damp litmus paper is necessary.
In simple words: Solid acids need moisture to show their acidic properties on indicators.

Exam Tip: Moisture is mandatory for acid-base indicator reactions.

Question 1. d) Can you check the evolution of CO2 chemically?
Answer: Yes, by passing the evolved gas through freshly prepared lime water (\(\text{Ca(OH)}_2\)), which turns milky due to the formation of insoluble calcium carbonate.
In simple words: Carbon dioxide turns lime water milky.

Exam Tip: This milky appearance test is the standard confirmatory test for carbon dioxide.

Question 2. a) What are acids?
Answer: Acids are chemical substances that have a sour taste, turn blue litmus red, and release hydronium ions (\(\text{H}_3\text{O}^+\)) in aqueous solution.
In simple words: Acids are sour substances that release hydrogen ions in water.

Exam Tip: Acids have pH values less than 7.

Question 2. b) Can presence of H+ ion in water be estimated? How?
Answer: Yes, using a pH meter or pH paper, which displays specific colors corresponding to hydrogen ion concentration.
In simple words: pH paper or a pH meter measures hydrogen ion concentration.

Exam Tip: Universal indicator/pH paper gives a color gradient based on \([\text{H}^+]\).

Question 2. c) How is pH related to strength of an acid?
Answer: Lower pH values indicate stronger acids with higher hydrogen ion concentrations.
In simple words: The lower the pH, the stronger the acid.

Exam Tip: Strong acids have pH 0 to 2.

Question 2. d) Name one strong acid and one weak acid.
Answer: Strong acid: Hydrochloric acid (\(\text{HCl}\)); Weak acid: Acetic acid (\(\text{CH}_3\text{COOH}\)).
In simple words: HCl is strong, and acetic acid (vinegar) is weak.

Exam Tip: Memorize common strong mineral acids (\(\text{HCl}, \text{H}_2\text{SO}_4, \text{HNO}_3\)).

Question 3. a) What are salts?
Answer: Salts are ionic compounds formed by the neutralization reaction between an acid and a base.
In simple words: Salts are formed when acids and bases neutralize each other.

Exam Tip: Acid + Base \(\rightarrow\) Salt + Water.

Question 3. b) How many types of salts are formed?
Answer: Salts are generally classified into neutral salts, acidic salts, and basic salts.
In simple words: Salts can be neutral, acidic, or basic depending on their parent acids and bases.

Exam Tip: Classification depends on the strength of the parent acid and base.

Question 3. c) What are neutral salts?
Answer: Salts formed by the neutralization of a strong acid and a strong base, having a pH of 7 (e.g., \(\text{NaCl}\)).
In simple words: Neutral salts come from strong acids and strong bases and have a neutral pH.

Exam Tip: Sodium chloride is a classic neutral salt.

Question 3. d) What do you mean by acidic salts?
Answer: Salts formed by the reaction of a strong acid and a weak base, having a pH less than 7 (e.g., \(\text{NH}_4\text{Cl}\)).
In simple words: Acidic salts are formed from strong acids and weak bases, making their solutions acidic.

Exam Tip: Ammonium chloride is an example of an acidic salt.

Question 3. e) Define basic salts.
Answer: Salts formed by the reaction of a weak acid and a strong base, having a pH greater than 7 (e.g., \(\text{CH}_3\text{COONa}\)).
In simple words: Basic salts are formed from weak acids and strong bases and have a basic pH.

Exam Tip: Sodium acetate is a basic salt.

Question 3. f) Give the corresponding acid and base from which sodium carbonate is formed.
Answer: Acid: Carbonic acid (\(\text{H}_2\text{CO}_3\)); Base: Sodium hydroxide (\(\text{NaOH}\)).
In simple words: Sodium carbonate is made from carbonic acid and sodium hydroxide.

Exam Tip: Sodium carbonate is a basic salt because NaOH is a strong base and carbonic acid is weak.

Question 4. a) What is common salt?
Answer: Sodium chloride (\(\text{NaCl}\)), an essential dietary salt obtained from seawater or rock salt deposits.
In simple words: Common salt is sodium chloride, used daily in food.

Exam Tip: NaCl is the primary raw material for many industrial chemicals.

Question 4. b) Why does common salt become moist in rainy season?
Answer: Common salt contains small amounts of impurities like magnesium chloride (\(\text{MgCl}_2\)) and calcium chloride (\(\text{CaCl}_2\)), which are deliquescent (absorb moisture from humid air).
In simple words: Impurities in common salt absorb moisture from humid rainy air, making it damp.

Exam Tip: Pure sodium chloride is not deliquescent; impurities cause the dampness.

Question 4. c) How is it used as a freezing mixture?
Answer: Mixing salt with ice lowers the freezing point of water (freezing point depression), creating temperatures below \(0^\circ\text{C}\) used for cooling.
In simple words: Salt mixed with ice melts the ice and lowers the temperature below freezing.

Exam Tip: This principle is used in making ice cream.

Question 4. d) Name two important laboratory chemicals prepared from common salt on large scale.
Answer: Sodium hydroxide (\(\text{NaOH}\)) and Sodium hydrogen carbonate (\(\text{NaHCO}_3\)) (or bleaching powder).
In simple words: Sodium hydroxide and baking soda are manufactured from common salt.

Exam Tip: Remember products of the chlor-alkali process.

Question 5. a) What is washing soda?
Answer: Sodium carbonate decahydrate, with the chemical formula \(\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}\).
In simple words: Washing soda is hydrated sodium carbonate used for cleaning and softening hard water.

Exam Tip: Note the 10 molecules of water of crystallization.

Question 5. b) Name the process by which sodium carbonate is manufactured.
Answer: Solvay process.
In simple words: The Solvay process is used to manufacture sodium carbonate industrially.

Exam Tip: Remember "Solvay process" for sodium carbonate manufacture.

Question 5. c) What are the raw materials used in the preparation of washing soda?
Answer: Sodium chloride (brine), ammonia, and limestone (calcium carbonate).
In simple words: Salt, ammonia, and limestone are the starting raw materials.

Exam Tip: List all three raw materials for complete credit.

Question 5. d) Sodium carbonate is obtained from another carbonate on heating. Name it.
Answer: Sodium hydrogen carbonate (Baking soda, \(\text{NaHCO}_3\)).
\(2\text{NaHCO}_3 \xrightarrow{\text{Heat}} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2\)
In simple words: Heating sodium bicarbonate produces sodium carbonate.

Exam Tip: Thermal decomposition of baking soda yields sodium carbonate.

Question 6. a) Name the substance used for bleaching cotton and wood pulp in textiles.
Answer: Bleaching powder (Calcium oxychloride, \(\text{CaOCl}_2\)).
In simple words: Bleaching powder is used to whiten cotton and wood pulp.

Exam Tip: Bleaching powder acts via the release of active chlorine.

Question 6. b) What is its chemical name?
Answer: Calcium oxychloride.
In simple words: Its chemical name is calcium oxychloride.

Exam Tip: Formula is \(\text{CaOCl}_2\).

Question 6. c) How is it manufactured?
Answer: By the action of chlorine gas on dry slaked lime: \(\text{Ca(OH)}_2 + \text{Cl}_2 \rightarrow \text{CaOCl}_2 + \text{H}_2\text{O}\)
In simple words: Passing chlorine over dry slaked lime produces bleaching powder.

Exam Tip: Ensure slaked lime is specified as dry.

Question 6. d) What is slaked lime?
Answer: Calcium hydroxide, \(\text{Ca(OH)}_2\).
In simple words: Slaked lime is calcium hydroxide.

Exam Tip: Formed by adding water to quicklime (\(\text{CaO}\)).

Question 6. e) Why does bleaching powder smell of chlorine?
Answer: Because it slowly reacts with carbon dioxide in the air to release chlorine gas.
In simple words: Reaction with atmospheric carbon dioxide releases free chlorine gas, which has a sharp smell.

Exam Tip: Chlorine gas gives bleaching powder its characteristic pungent odor.

ORAL QUESTIONS

Question 1. Name the acid present in lemon juice.
Answer: Citric acid.
In simple words: Lemons contain citric acid.

Exam Tip: Citrus fruits are rich in citric acid.

Question 2. What is the chemical difference between washing soda and baking powder?
Answer: Washing soda is hydrated sodium carbonate (\(\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}\)), whereas baking powder is a mixture of sodium hydrogen carbonate (\(\text{NaHCO}_3\)) and a mild edible acid like tartaric acid.
In simple words: Washing soda is sodium carbonate with water molecules, while baking powder is sodium bicarbonate mixed with an acid.

Exam Tip: Note the difference in chemical formulas and ingredients.

Question 3. Name the acid present in ant sting.
Answer: Formic acid (Methanoic acid, \(\text{HCOOH}\)).
In simple words: Ant stings inject methanoic acid.

Exam Tip: Formic acid causes irritation and pain upon ant stings.

Question 4. What is the ideal pH of the soil for the healthy growth of a plant?
Answer: Around 6.5 to 7.0 (neutral to slightly acidic).
In simple words: Plants grow best in neutral or slightly acidic soil.

Exam Tip: Extreme soil pH hinders nutrient absorption.

Question 5. At what pH the mouth teeth start decaying?
Answer: When the pH falls below 5.5.
In simple words: Tooth decay starts when mouth pH drops below 5.5.

Exam Tip: Acid corrosion of enamel starts below pH 5.5.

Question 6. How is pH of an acid solution affected when it is diluted?
Answer: The pH increases towards 7 as the concentration of hydrogen ions per unit volume decreases.
In simple words: Diluting an acid reduces its acidity, so its pH increases.

Exam Tip: Dilution decreases hydronium ion concentration, raising the pH.

Question 7. Name the gas responsible for extinguishing fire in a soda-acid fire extinguisher.
Answer: Carbon dioxide (\(\text{CO}_2\)) gas.
In simple words: Carbon dioxide puts out fires by cutting off oxygen.

Exam Tip: Carbon dioxide is heavier than air and blankets the fire.

Question 8. Out of glucose and acetic acid which one will conduct electricity in water?
Answer: Acetic acid, because it ionizes in water to release ions, whereas glucose dissolves as neutral molecules without forming ions.
In simple words: Acetic acid conducts electricity because it produces ions in water, while glucose does not.

Exam Tip: Only solutions containing mobile ions conduct electricity.

Question 9. What is the pH of blood?
Answer: Approximately 7.35 to 7.45 (slightly basic).
In simple words: Human blood is slightly alkaline with a pH around 7.4.

Exam Tip: Blood pH is tightly regulated within a narrow alkaline range.

Question 10. What is the chemical name of the compound which has the property of hardening when mixed with water?
Answer: Calcium sulfate hemihydrate (Plaster of Paris).
In simple words: Plaster of Paris hardens into gypsum when mixed with water.

Exam Tip: Hardening is due to rehydration back into gypsum.

QUIZ - WHO AM I

Question 1. I can roughly measure pH value from 0 - 14.
Answer: Universal indicator (or pH paper).
In simple words: Universal indicator shows a full spectrum of colors for pH 0 to 14.

Exam Tip: Universal indicators use color gradients to indicate pH.

Question 2. I am called antichlor and am used to remove excess chlorine from clothes when treated with bleaching powder.
Answer: Sodium thiosulfate (\(\text{Na}_2\text{S}_2\text{O}_3\)).
In simple words: Sodium thiosulfate neutralizes excess chlorine.

Exam Tip: Known as 'antichlor' in bleaching processes.

Question 3. I am a product of gypsum and am used to making chalks and fire proof materials.
Answer: Plaster of Paris (\(\text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O}\)).
In simple words: Plaster of Paris is made from gypsum.

Exam Tip: Used for casts, chalks, and fireproofing.

Question 4. I am a compound of calcium and can be used for disinfecting drinking water as well as for decolourisation.
Answer: Bleaching powder (Calcium oxychloride, \(\text{CaOCl}_2\)).
In simple words: Bleaching powder disinfects water and bleaches materials.

Exam Tip: Chlorine release provides the disinfectant property.

Question 5. I give different smell in acid and base solution.
Answer: Olfactory indicator (e.g., vanilla, clove oil, or onion extract).
In simple words: Olfactory indicators change their odor in acidic and basic solutions.

Exam Tip: Useful for visually impaired students.

Question 6. I am an oxide capable of showing properties for both acids and bases.
Answer: Amphoteric oxide (e.g., Zinc oxide \(\text{ZnO}\) or Aluminum oxide \(\text{Al}_2\text{O}_3\)).
In simple words: Amphoteric oxides react with both acids and bases.

Exam Tip: ZnO and \(\text{Al}_2\text{O}_3\) are classic examples.

Question 7. I am a covalent compound and conducts electricity in aqueous medium.
Answer: Hydrogen chloride (\(\text{HCl}\)).
In simple words: HCl is a covalent molecule that ionizes in water to conduct electricity.

Exam Tip: Covalent acids conduct electricity only when dissolved in water.

Question 8. I am a salt of potassium hydroxide and nitric acid.
Answer: Potassium nitrate (\(\text{KNO}_3\)).
In simple words: Potassium nitrate is formed from KOH and \(\text{HNO}_3\).

Exam Tip: Formed by neutralizing a strong acid with a strong base.

Question 9. I am the term used when a solid becomes liquid when exposed to moist air.
Answer: Deliquescence.
In simple words: Deliquescent substances absorb so much moisture from air that they dissolve into a liquid solution.

Exam Tip: Example: sodium hydroxide pellets or magnesium chloride.

Question 10. I am derived from tomato and turn blue litmus into red.
Answer: Oxalic acid.
In simple words: Tomatoes contain oxalic acid, which turns blue litmus red.

Exam Tip: Natural organic acids turn blue litmus red.

PUZZLES

Puzzle 1 Solutions:

Question 1. Across - 1. Known as vinegar (6)
Answer: ACETIC
In simple words: Dilute acetic acid is vinegar.

Exam Tip: 3-5% to 8% acetic acid in water is commercial vinegar.

Question 2. Across - 4. A mineral acid (12)
Answer: HYDROCHLORIC (or SULPHURIC ACID)
In simple words: Mineral acids are inorganic acids derived from minerals.

Exam Tip: Mineral acids include HCl, \(\text{H}_2\text{SO}_4\), and \(\text{HNO}_3\).

Question 3. Down - 2. Acid obtained from milk (6)
Answer: LACTIC
In simple words: Lactic acid is found in sour milk and curd.

Exam Tip: Produced by bacterial fermentation of milk sugar (lactose).

Question 4. Down - 3. An acid obtained from lemon (6)
Answer: CITRIC
In simple words: Lemon juice contains citric acid.

Exam Tip: Found abundantly in citrus fruits.

Puzzle 2 Solutions:

Question 5. Across - 1. A stone used for manufacture of sodium carbonate (9)
Answer: LIMESTONE
In simple words: Limestone supplies carbon dioxide and calcium for manufacturing processes.

Exam Tip: Limestone is chemically calcium carbonate (\(\text{CaCO}_3\)).

Question 6. Across - 3. A substance that changes colour in acid - base solution (9)
Answer: INDICATOR
In simple words: Indicators signal pH changes through color shifts.

Exam Tip: Examples include litmus, phenolphthalein, and methyl orange.

Question 7. Down - 2. A gas obtained in the electrolysis of sodium chloride (8)
Answer: CHLORINE (or HYDROGEN)
In simple words: Chlor-alkali process releases chlorine and hydrogen gases.

Exam Tip: Chlorine is collected at the anode.

Question 8. Down - 3. A substance that gives relief from acidity (7)
Answer: ANTACID
In simple words: Antacids neutralize stomach acid.

Exam Tip: Milk of magnesia (\(\text{Mg(OH)}_2\)) is a common antacid.

Crossword Puzzle (Acids and Bases) Solutions:

Across Clues:

Question 9. Across - 1. Name of acid in softdrink.[8]
Answer: CARBONIC
In simple words: Carbonic acid gives fizz to soft drinks.

Exam Tip: Formed by dissolving carbon dioxide in water.

Question 10. Across - 3. Chemical containing hydroxide ions.[4]
Answer: BASE
In simple words: Bases release hydroxide ions in water.

Exam Tip: Hydroxide ion is \(\text{OH}^-\).

Question 11. Across - 4. Chemical that is corrosive, has a sour taste and a pH less than 7.[4]
Answer: ACID
In simple words: Acids are sour, corrosive, and have low pH.

Exam Tip: Definition of an acid.

Question 12. Across - 6. Neutral substances have this pH.[5]
Answer: SEVEN
In simple words: Neutral substances have a pH of 7.

Exam Tip: Pure water at \(25^\circ\text{C}\) has pH 7.

Question 13. Across - 7. Alkalis have a pH _____ than 7.[4]
Answer: MORE
In simple words: Alkalis have a pH higher than 7.

Exam Tip: Basic range is from 7 to 14.

Question 14. Across - 9. Acid and base neutralise to form _____ and water.[4]
Answer: SALT
In simple words: Neutralization produces salt and water.

Exam Tip: Standard neutralization equation.

Question 15. Across - 11. Household bases are suitable for _____.[8]
Answer: CLEANING
In simple words: Bases are commonly used in soaps and cleaning agents.

Exam Tip: Bases feel soapy and remove grease.

Question 16. Across - 13. Chemical with a soapy feel and pH more than 7.[6]
Answer: ALKALI
In simple words: Alkalis feel soapy and have high pH.

Exam Tip: Soluble bases are alkalis.

Question 17. Across - 15. Acids change blue litmus paper _____.[3]
Answer: RED
In simple words: Acids turn blue litmus red.

Exam Tip: Remember: "An acid turns blue litmus red."

Question 18. Across - 18. Sulphuric acid turns litmus paper _____.[3]
Answer: RED
In simple words: Being an acid, sulfuric acid turns litmus red.

Exam Tip: All acids show the same litmus color change.

Question 19. Across - 19. Salt has this pH.[5]
Answer: SEVEN
In simple words: Neutral salts have a pH of 7.

Exam Tip: True for salts of strong acids and strong bases.

Question 20. Across - 21. Alkalis turn _____ paper blue.[6]
Answer: LITMUS
In simple words: Alkalis turn red litmus blue.

Exam Tip: Bases turn red litmus blue.

Question 21. Across - 22. Carbon dioxide and water form _____ acid.[8]
Answer: CARBONIC
In simple words: Dissolving carbon dioxide in water creates carbonic acid.

Exam Tip: Reaction: \(\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3\).

Question 22. Across - 25. Stomach acid.[12]
Answer: HYDROCHLORIC
In simple words: The stomach produces hydrochloric acid for digestion.

Exam Tip: Helps kill bacteria and activate digestive enzymes.

Down Clues:

Question 23. Down - 1. Many household _____ products are bases.[8]
Answer: CLEANING
In simple words: Household cleaners are typically basic.

Exam Tip: Detergents and soaps are basic.

Question 24. Down - 2. Indicator made from lichens.[6]
Answer: LITMUS
In simple words: Litmus is a natural dye extracted from lichens.

Exam Tip: Lichens belong to the division Thallophyta.

Question 25. Down - 3. Chemical that neutralises an acid.[4]
Answer: BASE
Answer: (or ALKALI)
In simple words: Bases neutralize acids.

Exam Tip: Neutralization is the core property of bases.

Question 26. Down - 5. Chemical that changes colour in acids and bases.[9]
Answer: INDICATOR
In simple words: Indicators signal pH changes through color variations.

Exam Tip: Essential laboratory testing tools.

Question 27. Down - 8. Common indicator used in liquid or paper form.[6]
Answer: LITMUS
In simple words: Litmus is widely used as a liquid or test paper.

Exam Tip: Most common classroom indicator.

Question 28. Down - 10. Soluble base.[6]
Answer: ALKALI
In simple words: Soluble bases are called alkalis.

Exam Tip: NaOH and KOH are soluble bases (alkalis).

Question 29. Down - 12. Common name for sodium hydroxide is _____ soda.[7]
Answer: CAUSTIC
In simple words: Sodium hydroxide is known as caustic soda.

Exam Tip: "Caustic" indicates its corrosive nature on skin.

Question 30. Down - 14. Common name for calcium hydroxide.[9]
Answer: SLAKEDLIME
In simple words: Calcium hydroxide is commonly called slaked lime.

Exam Tip: Formula is \(\text{Ca(OH)}_2\).

Question 31. Down - 16. Distilled water has this pH.[5]
Answer: SEVEN
In simple words: Pure distilled water is neutral with a pH of 7.

Exam Tip: Neutral pH corresponds to equal \(\text{H}^+\) and \(\text{OH}^-\) ions.

Question 32. Down - 17. Acids have a pH that is _____ than 7.[4]
Answer: LESS
In simple words: Acidic solutions have pH values less than 7.

Exam Tip: pH < 7 is acidic.

Question 33. Down - 20. _____ rain is an environmental problem in industrial areas.[4]
Answer: ACID
In simple words: Acid rain damages buildings, soils, and aquatic life.

Exam Tip: Caused by sulfur dioxide and nitrogen dioxide emissions.

Question 34. Down - 23. Reacts with a metal to form hydrogen gas and a salt.[4]
Answer: ACID
In simple words: Acids react with active metals to release hydrogen gas.

Exam Tip: Metal + Acid \(\rightarrow\) Salt + Hydrogen gas.

Question 35. Down - 24. Measure of amount of hydrogen ions released in solution.[2]
Answer: PH
In simple words: pH measures hydrogen ion concentration.

Exam Tip: Stands for 'Potential of Hydrogen'.