CBSE Class 10 Science NCERT Solutions: Acids, Bases and Salts

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NCERT Solutions PDF Class 10 PDF

This resource provides detailed NCERT Solutions for Class 10 Science, Chapter 2: Acids, Bases and Salts. It covers key concepts such as neutralization reactions, the properties of acids and bases, and the nature of various salts. The solutions explain the temperature changes during neutralization, how to reverse color changes with litmus, the role of drying agents like calcium chloride, and the composition of hydrated and anhydrous salts. It also delves into the acidic or basic nature of salts based on their parent acids and bases, and the chemical nature of tooth enamel. These solutions are designed to help students understand the fundamental principles of acids, bases, and salts, aiding in their exam preparation and revision.

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BoardCBSE
ClassClass 10
SubjectScience (Exemplar)
Session2026
LanguageEnglish
TypeNCERT Solutions
Chapter2. Acids, Bases and Salts

Chapter summary

This chapter focuses on the fundamental concepts of acids, bases, and salts. The NCERT Solutions cover neutralization reactions, including the energy changes involved, and the effect of acids and bases on indicators like litmus. It also explains the drying of gases and the concept of water of crystallization in salts. Furthermore, the solutions discuss the hydrolysis of salts to determine their acidic, basic, or neutral nature, and the chemical composition and properties of tooth enamel.

Learning outcomes

  • Understand the process and outcomes of mixing acids and bases.
  • Identify the role of acids and bases in changing litmus paper colors.
  • Explain the function of drying agents like calcium chloride.
  • Differentiate between salts with and without water of crystallization.
  • Determine the nature of a salt based on its parent acid and base.
  • Recognize the basic nature of calcium phosphate in tooth enamel.

Topics covered

Paper topics

  • Acids and Bases
  • Neutralization Reaction
  • Exothermic Reactions
  • Salt Formation
  • Litmus Indicator
  • pH Scale (implied)
  • Drying Agents
  • Water of Crystallization
  • Types of Salts
  • Basic Salts
  • Acidic Salts
  • Tooth Enamel Composition

Important topics

  • Neutralization Reactions and Temperature Changes
  • Role of Indicators (Litmus)
  • Water of Crystallization
  • Nature of Salts (Acidic, Basic, Neutral)
  • Chemical Composition of Tooth Enamel

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Questions and Solutions

Multiple Choice Questions - 1

1. What happens when a solution of an acid is mixed with a solution of a base in a test tube?

i) The temperature of the solution increases

ii) The temperature of the solution decreases

iii) The temperature of the solution remains the same

iv) Salt formation takes place

Solution: The correct option is (a) (i) and (iv).

When an acid reacts with a base, a neutralization reaction occurs. This reaction is exothermic, meaning it releases heat, causing the temperature of the solution to rise. Simultaneously, a salt and water are formed. Therefore, both the temperature increase and salt formation are observed.

Multiple Choice Questions - 2

2. 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

Solution: The correct option is (d) Hydrochloric acid.

Turning red litmus paper blue indicates that the solution is basic. To reverse this change, an acidic substance must be added. Among the given options, hydrochloric acid is a strong acid. Adding excess hydrochloric acid will neutralize the basic solution and turn the blue litmus paper red again.

Multiple Choice Questions - 3

3. During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through a guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is to:

a) absorb the evolved gas

b) moisten the gas

c) absorb moisture from the gas

d) absorb Cl- ions from the evolved gas

Solution: The correct option is (c) absorb moisture from the gas.

Hydrogen chloride gas can readily absorb moisture from the humid air. Calcium chloride (CaCl2) is a well-known drying agent or desiccant. When the gas is passed through a guard tube containing anhydrous calcium chloride, it absorbs the water vapor present in the gas, thereby drying it. This prevents the HCl gas from becoming damp.

Multiple Choice Questions - 4

4. Which of the following salts does not contain water of crystallisation?

a) Blue vitriol

b) Baking soda

c) Washing soda

d) Gypsum

Solution: The correct option is (b) Baking soda.

Water of crystallisation refers to the fixed number of water molecules bound within the crystal structure of a salt. Blue vitriol is copper(II) sulfate pentahydrate (CuSO4·5H2O), washing soda is sodium carbonate decahydrate (Na2CO3·10H2O), and gypsum is calcium sulfate dihydrate (CaSO4·2H2O). Baking soda, or sodium bicarbonate (NaHCO3), is an anhydrous salt and does not incorporate water molecules into its crystal structure.

Multiple Choice Questions - 5

5. Sodium carbonate is a basic salt because it is a salt of:

a) strong acid and strong base

b) weak acid and weak base

c) strong acid and weak base

d) weak acid and strong base

Solution: The correct option is (d) weak acid and strong base.

Sodium carbonate (Na2CO3) is formed from the reaction between sodium hydroxide (NaOH), a strong base, and carbonic acid (H2CO3), a weak acid. When such a salt dissolves in water, the carbonate ion (CO3^2-) undergoes hydrolysis, reacting with water to produce hydroxide ions (OH-), making the solution basic. Therefore, a salt formed from a weak acid and a strong base is basic in nature.

Multiple Choice Questions - 6

6. Calcium phosphate is present in tooth enamel. Its nature is:

a) basic

b) acidic

c) neutral

d) amphoteric

Solution: The correct option is (a) basic.

Calcium phosphate (Ca3(PO4)2) is a salt formed from calcium hydroxide (Ca(OH)2), a strong base, and phosphoric acid (H3PO4), which is a weak acid. Due to the presence of the phosphate ion (PO4^3-), which is the conjugate base of a weak acid, calcium phosphate exhibits basic properties in aqueous solutions. This basic nature helps to neutralize acids produced by bacteria in the mouth, protecting the tooth enamel.

Common mistakes

  • Confusing the direction of color change with litmus paper.
  • Misunderstanding the role of drying agents.
  • Incorrectly identifying the acidic or basic nature of salts.
  • Not recognizing the presence or absence of water of crystallization.

Revision tips

  • Review the concept of neutralization and its exothermic nature.
  • Memorize the color changes of litmus paper with acids and bases.
  • Understand why calcium chloride is used to dry gases.
  • Differentiate between hydrated and anhydrous salts.
  • Practice identifying the nature of salts based on their constituent acid and base.

Practice MCQs

Q1. When a solution of an acid is mixed with a solution of a base in a test tube, what are the likely observations?

Q2. An aqueous solution turns red litmus paper blue. Which of the following, if added in excess, would reverse this change?

Q3. During the preparation of hydrogen chloride gas, why is calcium chloride used in the guard tube?

Q4. Which of the following salts is typically anhydrous (does not contain water of crystallization)?

Q5. Sodium carbonate is considered a basic salt. This is because it is formed from the reaction of:

Q6. The primary component of tooth enamel, calcium phosphate, is characterized as:

Frequently asked questions

What happens when an acid and a base are mixed?

When an acid and a base are mixed, a neutralization reaction occurs, forming a salt and water. This reaction is typically exothermic, meaning it releases heat and increases the temperature of the solution.

How can the effect of a base on litmus paper be reversed?

If a basic solution turns red litmus paper blue, adding an excess amount of an acid, such as hydrochloric acid, will neutralize the base and reverse the color change back to red.

Why is calcium chloride used when preparing hydrogen chloride gas?

Calcium chloride is used as a drying agent to absorb any moisture present in the hydrogen chloride gas, ensuring that the gas collected is dry.

Which common salts do not contain water of crystallization?

Baking soda (Sodium bicarbonate) is an example of a salt that does not contain water of crystallization. Many other salts, like washing soda and gypsum, are hydrated.

How do we determine if a salt is acidic, basic, or neutral?

The nature of a salt depends on the strength of the acid and base from which it is formed. Salts formed from a strong acid and a weak base are acidic, from a weak acid and a strong base are basic, and from a strong acid and a strong base are neutral.

What is the nature of tooth enamel?

Tooth enamel is primarily composed of calcium phosphate, which is a basic salt. This basic nature helps protect teeth from acids.

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