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

NCERT Solutions for class 10 Science Chapter 2 Exercise Question

Question 1

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

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

Answer

10 is the answer because When litmus paper turns red to blue when reacts with basic solution.Range of pH value of basic solution is 7 to 14

Question 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

Answer is HCl.

The egg-shells are made up of calcium carbonate. When it reacts with HCl it give CO²gas which turns lime water milky.

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

Question 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) 16mL because 10 ml of NaOH requires 8 mL of HCL, 20 ml of NaOH require 16mL of HCl.

Question 4

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

(a) Antibiotic (b) Analgesic (c) Antacid (d) Antiseptic

Answer

Excess production of acid in the stomach cause indigestion. Medicines Antacid used to treat indigestion .

Question 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:

dilute sulphuric acid + zinc → Zinc Sulphate + Hydrogen Gas

H₂SO₄(aq) + Zn → ZnSO₄(aq) + H₂(g)

(b) dilute hydrochloric acid reacts with magnesium ribbon.

dilute Hydrochloric + Magnesium → Magnesium Chloride + Hydrogen Gas

2HCl(aq) + Mg → MgCl₂(aq) + H₂(g)

(c) dilute sulphuric acid reacts with aluminium powder.

dilute Sulphuric Acid + Aluminium → Aluminium Sulphate + Hydrogen Gas

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

(d) dilute hydrochloric acid reacts with iron filings.

dilute Hydrochloric Acid + Iron → Ferrous Chloride + Hydrogen Gas

6HCl(aq) + 3Fe(s) → 3FeCl₂(aq) + 3H₂(g)

Question 6

Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it

Answer

Alcohols and glucose contain hydrogen but they are not cosider as acid because they not give H⁺ ions in solution .

• Take solutions of glucose, alcohol, hydrochloric acid, sulphuric acid, etc.
• Fix two nails on a cork, and place the cork in
a 100 mL beaker.
• Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch
• Now pour some dilute HCl in the beaker and switch on the current.
• Repeat with dilute sulphuric acid.
• What do you observe?
• Repeat the experiment separately with glucose and alcohol solutions. What do you observe now?
• Does the bulb glow in all cases?

Question 7

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

Answer

Distilled water not conduct electricity because it is pure form of water it does not contain any ionic compounds in it.While rainwater contain dissolved gases like CO₂ ,O₂ etc. and form acid like carbonic acid which dissociate into ions hence rainwater conduct electricity.

Question 8

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

Answer

Acidic nature of a substance due to formation of H⁺ ions. Hydrogen ions can only be produced in the presence of water .So acids not show acidic behaviour in the absence of water

Question 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?

Answer

pH11 – Strongly alkaline

pH9 – weakly alkaline

PH7 – Neutral

pH4 – Weakly acidic

pH1 – Strongly acidic

Question 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

HCl is more reactive than acetic acid. Fizzing occurs due to the production of the hydrogen gas when reaction of the acid with magnesium ribbon. Since HCl produce more hydrogen gas which causes fizzing more vigorously.hence more fizzing take place in test tube A.

Question 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

The pH of fresh milk is 6 which is acidic in nature.Fresh milk is turned to curd due to action of lactic acid. Lactic acid reduces the pH of the milk.

Question 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) He shifted the pH of the fresh milk from 6 to slightly alkaline to making the milk more alkaline,Its prevent milk from getting sour due to action of lactic acid.

(b) Milk takes long time to set into curd because the lactic acid produced here first neutralises by using baking soda.So it take long time to turn milk to curd.

Question 13

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

Answer

Because plaster of Paris convert into gypsum after reacting with moisture present in air. This will turn plaster useless.

Question 14

What is a neutralisation reaction? Give two examples.

Answer

neutralisation reaction in which acid react with base to form salt and water .

Examples:

NaOH + HCl → NaCl + H₂O

KOH + HNO³ → KNO³ + H²O

Question 15

Give two important uses of washing soda and baking soda.

Answer

Washing soda

1. It is used for removing permanent hardness of water.
2. Sodium carbonate can be used as a cleaning agent for domestic purposes.

Baking soda

1.It is also used in soda-acid fire extinguisher
2. Sodium hydrogencarbonate is also an ingredient in antacids. it neutralises excess acid in the stomach and provides relief.