NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Chapter 2 Acids, Bases and Salts NCERT Solutions for Class 10 Science is available on this page that will definitely useful in improving marks in the board examinations. It will make learning and understanding more easier with detailed and accurate Class 10 NCERT Solutions. You can track your progress anytime and provide complete assistance with these NCERT Solutions.

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Chapter 2 Acids, Bases and Salts Class 10 Science NCERT Solutions


NCERT In Text Questions

Page No: 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?

Solution

• If the colour of red litmus does not change then it is acid.
• If the colour of red litmus changes to blue then it is base.
• If there is slight change in the colour of red litmus (such as purple) then it is distilled water.

Page No: 22

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

Solution

Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, thereby spoiling the food.

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?

Solution

Hydrogen gas is usually liberated when an acid reacts with a metal.
To test the presence of gas, we need to take a few pieces of zinc granules and add 5 ml of dilute H, SO4. Shake it and pass the gas produced into a soap solution. The bubbles of the soap solution are formed. These soap bubbles contain hydrogen gas.
H2SO4 + Zn → ZnSO4 + H2 ↑
We can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the soap bubbles.

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.

Solution

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)
Calcium Carbonate + Hydrochloric acid → Calcium Chloride + Carbon dioxide + Water

Page No: 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?

Solution

HCl and HNO3 etc. dissociate in presence of water to form hydrogen ions (H2). These hydrogen ions combine with H2O to form hydronium ions (H3O+).
HCl (aq) → H+ + Cl-
H+ + H2O → H3O+
When alcohols and glucose are mixed with water then they do not dissolve to form ions. Hence they do not show acidic character.

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

Solution

In an aqueous solution, an acid dissociates to produce H+ ions or H2O+ ions. Due to the presence of ions, the aqueous solution of an acid conducts electricity.

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

Solution

Dry HCl gas not change the colour of the dry litmus paper because it has no Hydrogen ions (H+) in it.

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

Solution

The process of dissolving an acid or base in water is exothermic. The acids particularly mineral acids must always be added slowly to water with constant stirring. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.

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

Solution

The concentration of hydronium ions (H3O+) decreases when solution of an acid is diluted with water.

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

Solution

The concentration of hydroxide ions (OH) would increase when excess base is dissolved in a solution of sodium hydroxide.

Page No: 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?

Solution

As the pH of a solution is inversely proportional to its H+ ion concentration. Thus, the solution A with pH 6 has more H+ ion concentration than the solution B with pH 8. For an acidic solution, the pH lies between 0 to 7 and for a basic solution the pH range is 7-14. Thus, A with pH 6 is acidic and B with pH 8 is basic.

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

Solution

If the concentration of H+ (aq) ions is increased (>10-7) then the solution become acidic and if the concentration of H+ (aq) ions is decreased (<10-7) then the solution become basic in nature.

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

Solution

Yes, basic solution also has H+ ions. However, their concentration is less as compared to the concentration of OH- ions that makes the solution 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)?

Solution

If the soil is acidic and improper for cultivation, then to increase the basicity of soil, the farmer would treat the soil with quick lime or slaked lime or chalk.

Page No: 33

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

Solution

Bleaching Powder.

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

Solution

Calcium hydroxide [Ca(OH)2]

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

Solution

Washing soda (Na2CO3.10H2O)

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

Solution

When sodium hydrogen carbonate is heated then sodium carbonate and water is formed along with the evolution of carbon dioxide gas.

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

Solution


Page No: 34

Exercises

1. A solution turns red litmus blue, its pH is likely to be
(a) 1
(b) 4
(c) 5
(d) 10

Solution

(d) 10

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

Solution

(b) HCl

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 of HCl solution (the same solution as before) required to neutralise it will be
(a) 4 mL
(b) 8mL
(c) 12 mL
(d) 16 mL

Solution

(d) 16 mL

4. Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic

Solution

(c) Antacid

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.

Solution

(a) H2SO4 (aq) + Zn (s) → ZnSO4 (aq) + H2 (g)

(b) 2HCl (aq) + Mg (s) → MgCl2 (aq) + H2 (g)

(c) 3H2SO4 (aq) + 2Al (s) → Al2(SO4)3 (aq) + 3H2 (g)

(d) 6HCl (aq) + 2Fe (s) → 2FeCl3 (aq) + 3H2 (g)

6. Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an activity to prove it.

Solution

Two nails are fitted on a cork and are kept it in a 100 mL beaker. The nails are then connected to the two terminals of a 6-volt battery through a bulb and a switch. Some dilute HCl is poured in the beaker and the current is switched on. The same experiment is then performed with glucose solution and alcohol solution.

Observation:
It will be observed that the bulb glows in the HCl solution and does not glow in the glucose solution.


Result:
HCl dissociates into H+and Cl−ions. These ions conduct electricity in the solution resulting in the glowing of the bulb. On the other hand, the glucose solution does not dissociate into ions. Therefore, it does not conduct electricity.

Conclusion:
From this activity, it can be concluded that all acids contain hydrogen but not all compounds containing hydrogen are acids.
That is why, though alcohols and glucose contain hydrogen, they are not categorised as acids.

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

Solution

Distilled water does not conduct electricity because it does not contain any ionic compounds (like acids, bases or salts) dissolved in it. When rain water falls to the earth through the atmosphere, it dissolves an acidic gas “carbon dioxide from the air and forms some carbonic acid (H2CO3). Carbonic acid provides some hydrogen ions and carbonate ions to rain water. Thus, due to the presence of these ions, rain water conducts electricity.

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

Solution

The acidic behaviour of acids is due to the presence of hydrogen ions, H+ (aq) ions. The acids produce hydrogen ions only on dissolving in water. In the absence of water, acids do not produce hydrogen ions and hence do not show acidic behaviour.

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.

Solution

(a) Neutral →Solution D with pH 7
(b) Strongly alkaline →Solution C with pH 11
(c) Strongly acidic →Solution B with pH 1
(d) Weakly acidic →Solution A with pH 4
(e) Weakly alkaline →Solution E with pH 9
The pH can be arranged in the increasing order of the concentration of hydrogen ions as: 11 < 9 < 7 < 4 < 1.

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. In which test tube will the fizzing occur more vigorously and why?

Solution

The fizzing will occur strongly in test tube A, in which hydrochloric acid (HCl) is added. This is because HCl is a stronger acid than CH3COOH and therefore produces hydrogen gas at a faster speed due to which fizzing occurs.

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

Solution

Fresh milk has a pH 6. During curdling, bacteria keeps growing and it breaks down the lactose into lactic acid which acidifies the milk even further. Therefore, the pH of the milk will decrease. More acidic the substance, lower is the pH, so it becomes more acidic.

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?

Solution

(a) We know that the pH of fresh milk is 6, thus it is slightly acidic due to the presence of lactic acid in it. Milkman adds a very small amount of baking soda to fresh milk to make the medium slightly alkaline. The base released by baking soda will neutralise the effect of lactic acid present in milk and helps to check the milk getting sour.

(b) When milk sets as curd, the pH decreases so it becomes more acidic. In case of alkaline medium due to addition of baking soda, it will take longer time to achieve acidic medium back so that milk may set as curd.

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

Solution

The Plaster of Paris should be stored in a moisture-proof container as it absorbs water from moisture and turn into hard substance (Gypsum).

14. What is a neutralization reaction? Give two examples.

Solution

A reaction which occurs between an acid and a base to produce salt and water is known as neutralisation reaction.
Acid + Base → Salt + Water
(i) NaOH + HCl → NaCl + H2O
(ii) HNO3 + KOH → KNO3 + H2O

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

Solution

(a) Uses of washing soda:
(i) Washing soda is used as a cleansing agent for domestic purposes like washing clothes.
(ii) It is used for removing permanent hardness of water.

(b) Uses of baking soda:
(i) Baking soda is used as an antacid in medicine to remove acidity of the stomach.
(ii) Baking soda is used in making baking powder.

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