NCERT Solutions For Class 10 Chapter 2 Acids, Bases and Salts, Download PDF

NCERT Class 10 Science Chapter 2 Intext Question Answer: The National Council of Educational Research and Training (NCERT) has revised the Class 10 Science textbooks. Therefore, students require an updated solution manual to precisely guide them through the questions and their solutions. The exercise questions have also faced changes. Thus, having the updated solutions will save you from preparing deleted questions. Check here the NCERT solutions for Class 10 Science, Acids, Bases, and Salts.

NCERT Class 10 Acids, Bases and Salts Solutions

Here, the complete solution manual is provided for Chapter 2 of NCERT Class 10 science textbook. Get here answers to all intext and exercise questions.

NCERT Class 10 Science Chapter 2 Intext Question Answer Page Number 18

1. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

Answer: To identify the contents of the three test tubes using only red litmus paper:

1. Test each solution: Dip red litmus paper into each test tube.
2. Identify the basic solution: The red litmus paper will turn blue in the basic solution.
3. Identify the acidic solution: The red litmus paper will stay red in the acidic solution.
4. Identify the distilled water: After testing the first two, the remaining test tube is distilled water, where the red litmus paper will also stay red.

This way, you can easily identify the acidic, basic, and neutral (distilled water) solutions.

NCERT Class 10 Science Chapter 2 Intext Question Answer Page Number 22

1. Why should curd and sour substances not be kept in brass and copper vessels?

Answer: Curd and sour substances should not be kept in brass and copper vessels because they contain acids, like lactic acid in curd. These acids react with brass or copper, which can release harmful substances into the food. This reaction may lead to food poisoning and can make the food unsafe to eat. Additionally, it can also damage the vessel over time. Using stainless steel or glass containers is a safer option for storing such acidic substances.

2. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?

Answer: When an acid reacts with a metal, hydrogen gas is usually liberated.

Example: When hydrochloric acid (HCl) reacts with zinc (Zn), hydrogen gas is released: Zn+2HCl→ZnCl₂+H₂↑

Test for Hydrogen Gas: To test for hydrogen, bring a burning matchstick near the gas. If hydrogen is present, it burns with a 'pop' sound. This confirms the presence of hydrogen gas.

3. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

Answer: The metal compound A is calcium carbonate (CaCO₃). When calcium carbonate reacts with dilute hydrochloric acid (HCl), it produces carbon dioxide (CO₂), which causes effervescence. Carbon dioxide extinguishes a burning candle. The reaction also forms calcium chloride (CaCl₂) and water (H₂O).

Balanced Chemical Equation: CaCO₃+2HCl→CaCl₂+H₂O+CO₂

This is the balanced equation for the reaction.

NCERT Class 10 Science Chapter 2 Intext Question Answer Page Number 25

1. Why do HCl, HNO3 , etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character? 

Answer: HCl (hydrochloric acid) and HNO₃ (nitric acid) show acidic characters in aqueous solutions because they ionise completely in water, releasing H⁺ ions, which cause acidity. In contrast, compounds like alcohol and glucose do not ionise in water to produce H⁺ ions. Therefore, they do not show acidic behaviour. Acidity in a solution depends on the presence of free H⁺ ions, and since alcohol and glucose do not release these ions, they remain neutral in water

2. Why does an aqueous solution of an acid conduct electricity?

Answer: An aqueous solution of an acid conducts electricity because acids dissociate into ions when dissolved in water. These ions, mainly hydrogen ions (H⁺) and negative ions, are charged particles that move freely in the solution. When an electric current is applied, these ions carry the charge, allowing electricity to flow through the solution.

3. Why does dry HCl gas not change the colour of the dry litmus paper?

Answer: Dry HCl gas does not change the colour of dry litmus paper because it does not release hydrogen ions (H⁺) in the absence of water. HCl gas shows acidic properties only when dissolved in water, as it ionises to form H⁺ ions, which are responsible for the colour change in litmus paper. Without moisture, there are no H⁺ ions to cause the reaction.

4. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

Answer: When diluting an acid, it is recommended to add acid to water, not water to acid, because this process releases a lot of heat. Adding water to acid can cause the acid to splash and lead to accidents due to the sudden heat release. However, if acid is slowly added to water, the heat is spread out more safely, and the water absorbs it gradually, reducing the risk of splashing and burns. This is a safety measure to prevent harmful reactions and ensure controlled dilution.

Also Read:

• Best Books for 6–8 Years: Check Summary, and Unique Features
• Best Horror Books for Teens

5. How is the concentration of hydronium ions (H₃O⁺ ) affected when a solution of an acid is diluted?

Answer: When an acid solution is diluted, the concentration of hydronium ions (H₃O⁺) decreases. This happens because adding more water increases the total volume of the solution, spreading the H₃O⁺ ions over a larger volume. As a result, the number of H₃O⁺ ions per unit volume becomes lower, making the solution less acidic. However, the total number of H₃O⁺ ions remains the same, only their concentration reduces.

6. How is the concentration of hydroxide ions (OH ^– ) affected when excess base is dissolved in a solution of sodium hydroxide?

Answer: When excess base is dissolved in a solution of sodium hydroxide (NaOH), the concentration of hydroxide ions (OH⁻) increases. Sodium hydroxide is a strong base that fully dissociates in water, releasing hydroxide ions. Adding more base means more OH⁻ ions are produced, raising their concentration in the solution. So, with more base, there are more OH⁻ ions present, making the solution even more basic.

NCERT Class 10 Science Chapter 2 Intext Question Answer Page Number 28

1. You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?

Answer: Solution A, with a pH of 6, has more hydrogen ions compared to Solution B, which has a pH of 8. This is because a lower pH means higher hydrogen ion concentration.

• Solution A (pH 6) is acidic because its pH is less than 7.
• Solution B (pH 8) is basic because its pH is more than 7.

2. What effect does the concentration of H+ (aq) ions have on the nature of the solution?

Answer: The concentration of H⁺ (aq) ions affects whether a solution is acidic or basic.

• Acidic Solution: If a solution has a high concentration of H⁺ ions, it is acidic. This means it has a lot of hydrogen ions, which makes it sour and able to turn blue litmus paper red. For example, lemon juice and vinegar are acidic.
• Basic Solution: If a solution has a low concentration of H⁺ ions, it is basic (or alkaline). This means it has fewer hydrogen ions and can turn red litmus paper blue. For example, soap and baking soda solutions are basic.

So, more H⁺ ions mean an acidic solution, and fewer H⁺ ions mean a basic solution.

3. Do basic solutions also have H⁺ (aq) ions? If yes, then why are these basic?

Answer: Yes, basic solutions do have H⁺ (aq) ions, but in very small amounts. A basic solution is one where the concentration of OH⁻ (hydroxide) ions is higher than the concentration of H⁺ ions. In other words, the solution has more OH⁻ ions compared to H⁺ ions. This makes the solution "basic" or "alkaline." Even though there are H⁺ ions present, their low concentration compared to OH⁻ ions is why the solution is considered basic.

4. Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?

Answer: A farmer would treat the soil with quick lime, slaked lime, or chalk if the soil is too acidic. These substances help to make the soil less acidic by adding calcium.

• Quick Lime (Calcium Oxide): Used to quickly adjust soil pH, but it must be handled carefully as it can be very strong and irritating.
• Slaked Lime (Calcium Hydroxide): Safer to use than quick lime and helps to neutralise soil acidity gradually.
• Chalk (Calcium Carbonate): Commonly used to improve soil over time, especially in areas where the soil needs less immediate change.

These treatments help crops grow better by making the soil more balanced.

Also Read:

• Types of Waves in Physics
• Avogadro’s Number: Definition, Value, Meaning, Unit and Symbol
• Magnetic Field: Formula, Properties, and Applications
• Archimedes' Principle: Formula, Derivation, Applications and Examples

NCERT Class 10 Science Chapter 2 Intext Question Answer Page Number 33

1. What is the common name of the compound CaOCl₂?

Answer: The common name of the compound CaOCl₂ is bleaching powder.

2. Name the substance which on treatment with chlorine yields bleaching powder.

Answer: The substance that, when treated with chlorine, yields bleaching powder is calcium hydroxide.

3. Name the sodium compound which is used for softening hard water.

Answer: The sodium compound used for softening hard water is sodium carbonate, commonly known as washing soda.

4. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.

Answer: When a solution of sodium bicarbonate (also known as sodium hydrocarbonate) is heated, it decomposes to form sodium carbonate, carbon dioxide, and water. The reaction is:

2NaHCO3(s)→Na2CO3(s)+CO2(g)+H2O (l)

In simple terms, heating sodium bicarbonate causes it to break down, releasing carbon dioxide gas and water while forming sodium carbonate.

5. Write an equation to show the reaction between Plaster of Paris and water. 

Answer: Plaster of Paris (POP) is a hemihydrate of calcium sulfate, meaning it has half a molecule of water attached to each calcium sulfate molecule. Its chemical formula is CaSO₄·½H₂O.

When POP is mixed with water, it reacts to form calcium sulfate dihydrate (gypsum). This reaction is exothermic, meaning it releases heat.

Here's the balanced chemical equation for the reaction:

CaSO₄·½H₂O + 1.5H₂O → CaSO₄·2H₂O

In simpler terms, Plaster of Paris plus water equals gypsum.

NCERT Class 10 Science Chapter 2 Exercise Questions

1. A solution turns red litmus blue, its pH is likely to be

(a) 1 (b) 4 (c) 5 (d) 10

Answer: (d) 10

Explanation: A solution that turns red litmus blue is basic, and a pH of 10 indicates a basic solution.

2. A solution reacts with crushed egg-shells to give a gas that turns lime-water milky.

The solution contains

(a) NaCl (b) HCl (c) LiCl (d) KCl

Answer: (b) HCl

Explanation: Egg-shells contain calcium carbonate, which reacts with hydrochloric acid (HCl) to produce carbon dioxide gas. This gas turns lime-water milky due to the formation of calcium carbonate.

3. 10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a

given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount

HCl solution (the same solution as before) required to neutralise it will be

(a) 4 mL (b) 8 mL (c) 12 mL (d) 16 mL

Answer: (d) 16 mL

Explanation: Doubling the volume of NaOH will require twice the volume of HCl to neutralise it.

4. Which one of the following types of medicines is used for treating indigestion?

(a) Antibiotic

(b) Analgesic

(c) Antacid

(d) Antiseptic

Answer: (c) Antacid

Explanation: Antacids are used to neutralise excess stomach acid and relieve indigestion.

5. Write word equations and then balanced equations for the reaction taking place when –

(a) dilute sulphuric acid reacts with zinc granules.

(b) dilute hydrochloric acid reacts with magnesium ribbon.

(c) dilute sulphuric acid reacts with aluminium powder.

(d) dilute hydrochloric acid reacts with iron filings.

Answer: (a) Dilute sulphuric acid reacts with zinc granules:

Word equation: Sulphuric acid + Zinc → Zinc sulphate + Hydrogen gas
Balanced equation:

H2SO4+Zn→ZnSO4+H2

(b) Dilute hydrochloric acid reacts with magnesium ribbon:

Word equation: Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen gas
Balanced equation:

2HCl+Mg→MgCl2+H2

(c) Dilute sulphuric acid reacts with aluminium powder:

Word equation: Sulphuric acid + Aluminium → Aluminium sulphate + Hydrogen gas
Balanced equation:

3H2SO4+2Al→Al2(SO4)3+3H2

(d) Dilute hydrochloric acid reacts with iron filings:

Word equation: Hydrochloric acid + Iron → Iron chloride + Hydrogen gas
Balanced equation:

6HCl+2Fe→2FeCl3+3H2

6. Compounds such as alcohols and glucose also contain hydrogen but are not

categorised as acids. Describe an Activity to prove it.

Answer: Activity to prove that alcohols and glucose contain hydrogen but are not acids:

• Take two beakers. In one, dissolve some glucose in water, and in the other, dissolve some alcohol in water.
• Connect each beaker to a bulb and battery in a simple circuit (electrolyte tester).
• Observe that the bulb does not glow in either beaker.

Conclusion: Even though glucose and alcohol contain hydrogen, they do not ionise in water to produce hydrogen ions (H+), and thus, they do not conduct electricity or behave as acids.

7. Why does distilled water not conduct electricity, whereas rain water does?

Answer: Distilled water does not conduct electricity because it is pure and does not contain any dissolved salts or ions. On the other hand, rainwater contains dissolved carbon dioxide and other impurities, forming ions that allow it to conduct electricity.

8. Why do acids not show acidic behaviour in the absence of water?

Answer: Acids do not show acidic behaviour in the absence of water because they need to dissolve in water to ionise and produce hydrogen ions (H+), which are responsible for their acidic properties. In the absence of water, the acid molecules cannot dissociate into ions.

9. Five solutions A,B,C,D and E when tested with universal indicator showed pH as 4,1,11,7 and 9, respectively. Which solution is (a) neutral? (b) strongly alkaline? (c) strongly acidic? (d) weakly acidic? (e) weakly alkaline? Arrange the pH in increasing order of hydrogen-ion concentration.

Answer: (a) Neutral D (pH 7)
(b) Strongly alkaline C (pH 11)
(c) Strongly acidic B (pH 1)
(d) Weakly acidic A (pH 4)
(e) Weakly alkaline E (pH 9)

Increasing order of hydrogen ion concentration: C (pH 11), E (pH 9), D (pH 7), A (pH 4), B (pH 1)
(Note: Lower pH indicates higher hydrogen ion concentration).

10. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?

Answer: Fizzing will occur more vigorously in test tube A (with HCl) because hydrochloric acid is a strong acid, which ionises completely in water, releasing more hydrogen ions (H+). These hydrogen ions react with magnesium more vigorously, producing more hydrogen gas. Acetic acid in test tube B is a weak acid and only partially ionises, resulting in less fizzing.

11. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.

Answer: As milk turns into curd, its pH will decrease (become more acidic). This happens because bacteria present in milk convert lactose into lactic acid during the curdling process, lowering the pH.

12. A milkman adds a very small amount of baking soda to fresh milk. (a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline? (b) Why does this milk take a long time to set as curd?

Answer: (a) Baking soda (sodium bicarbonate) is a weak base. It neutralises some of the acids in milk, making the milk slightly alkaline to prevent it from turning sour quickly.

(b) Curd formation requires an acidic environment. By making the milk slightly alkaline, the milkman slows down the acidification process, delaying the curd formation.

13. Plaster of Paris should be stored in a moisture-proof container. Explain why?

Answer: Plaster of Paris (calcium sulphate hemihydrate) reacts with water to form gypsum, which hardens. If exposed to moisture, Plaster of Paris will absorb water from the air and lose its effectiveness as it hardens prematurely. Storing it in a moisture-proof container prevents this reaction.

14. What is a neutralisation reaction? Give two examples.
    Answer: A neutralisation reaction is a chemical reaction in which an acid reacts with a base to form salt and water, and the pH moves closer to 7.
    Examples:

• Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water
  HCl+NaOH→NaCl+H₂O
• Sulphuric acid + Potassium hydroxide → Potassium sulphate + Water
  H₂SO₄+2KOH→K₂SO₄+2H₂O

15. Give two important uses of washing soda and baking soda.

Answer: Washing soda (sodium carbonate):

1. Used as a cleaning agent in households to remove dirt and grease.
2. Used in the manufacturing of glass, paper, and soap.

Baking soda (sodium bicarbonate):

1. Used as a leavening agent in baking, causing dough to rise.
2. Used as an antacid to relieve indigestion and heartburn.

Check:

• CBSE Class 10 Mock Test Videos For Quick Revision
• CBSE Class 10 Science Lab Manual PDF