CBSE Class 7 Science Exemplar Chapter 5: Acids, Bases and Salts NCERT Solutions

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 7 PDF

This chapter delves into the fundamental concepts of acids, bases, and salts, crucial for Class 7 Science students. The NCERT Solutions for Chapter 5 provide clear explanations and step-by-step solutions to various questions, including multiple-choice and descriptive types. Key topics covered include the properties of acids and bases, the role of indicators like turmeric and phenolphthalein, the process of neutralization reactions, and practical applications such as improving soil quality. These solutions are designed to help students grasp the scientific principles involved, understand the reactions, and prepare effectively for their examinations by reinforcing their knowledge of chemical concepts.

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Board	CBSE
Class	Class 7
Subject	Science Exemplar
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 5

Chapter summary

Chapter 5 of the CBSE Class 7 Science Exemplar focuses on Acids, Bases, and Salts. The NCERT Solutions cover essential concepts like identifying acids and bases using natural and synthetic indicators, understanding the exothermic nature of mixing acids with water, and the products of neutralization reactions (salt and water). It also addresses practical applications like treating basic soil with organic matter and identifying the source of litmus indicator. The solutions aim to clarify these concepts for students.

Learning outcomes

Understand the correct procedure for diluting acids.
Identify the products of a neutralization reaction.
Recognize the color changes of natural indicators (turmeric) in acidic and basic solutions.
Determine the colors of synthetic indicators (phenolphthalein) in acidic and basic solutions.
Explain how to improve the quality of basic soil.
Identify the source of the natural indicator litmus.

Topics covered

Paper topics

Acids
Bases
Salts
Indicators
Natural Indicators
Synthetic Indicators
Neutralization Reaction
pH and Soil Treatment
Litmus
Turmeric
Phenolphthalein

Important topics

Safe dilution of acids
Neutralization reaction products
Indicator color changes (Turmeric, Phenolphthalein, Litmus)
Treating basic soil

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Questions and Solutions

Multiple Choice Questions

1. The correct way of making a solution of acid in water is to

(a) add water to acid.

(b) add acid to water.

(d) add water to acid in a shallow container.

Solution: The correct and safe method is to gradually add the acid to water. This is because the process of diluting concentrated acids is highly exothermic, meaning it releases a significant amount of heat. If water is added to acid, the heat generated can cause the water to boil rapidly and splash the corrosive acid, leading to potential injury. By adding acid to water, the larger volume of water can absorb and dissipate the heat more effectively, making the process safer. Therefore, the correct option is (b).

2. Products of a neutralisation reaction are always

(a) an acid and a base.

(b) an acid and a salt.

(d) a salt and a base.

Solution: A neutralization reaction occurs when an acid reacts with a base. In this chemical reaction, the acidic properties of the acid and the basic properties of the base cancel each other out. The typical products formed from the reaction of an acid and a base are a salt and water. For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), the products are sodium chloride (NaCl), which is a salt, and water (H₂O). Thus, the correct option is (c).

3. Turmeric is a natural indicator. On adding its paste to acid and base separately, which colours would be observed

(a) Yellow in both acid and base.

(b) Yellow in acid and red in base.

(d) Red in acid and blue in base.

Solution: Turmeric is a natural indicator that is yellow in color. When turmeric paste is added to an acidic solution, its yellow color remains unchanged because acids do not react with turmeric in a way that alters its color. However, when turmeric paste is added to a basic solution, a chemical reaction occurs, causing the turmeric to change its color from yellow to red. This color change helps to identify the presence of a base. Therefore, the observed colors are yellow in acid and red in base, making option (b) correct.

4. Phenolphthalein is a synthetic indicator and its colours in acidic and basic solutions, respectively are

(a) red and blue.

(b) blue and red.

(d) colourless and pink.

Solution: Phenolphthalein is a synthetic chemical indicator commonly used in titrations. Its color changes depending on the pH of the solution. In acidic solutions, phenolphthalein remains colorless. However, when it comes into contact with a basic (alkaline) solution, it exhibits a distinct pink color. Therefore, the colors observed in acidic and basic solutions, respectively, are colorless and pink. This corresponds to option (d).

5. When the soil is too basic, plants do not grow well in it. To improve its quality what must be added to the soil?

(a) Organic matter

(b) Quick lime

(d) Calamine solution

Solution: When soil becomes too basic (alkaline), it can hinder plant growth. To correct this, a substance that can neutralize the base needs to be added. Organic matter, such as compost or manure, is acidic in nature. When added to basic soil, the organic matter reacts with and neutralizes the excess base, thereby lowering the pH of the soil and making it more suitable for plant growth. Quick lime (calcium oxide) and slaked lime (calcium hydroxide) are basic substances themselves and would further increase the alkalinity of the soil. Calamine solution is a mixture of zinc oxide and zinc carbonate, primarily used for skin conditions, not soil treatment. Therefore, organic matter is the appropriate addition to improve basic soil quality, making option (a) correct.

6. 'Litmus', a natural dye is an extract of which of the following?

(a) China rose (Gudhal)

(b) Beetroot

(d) Blue berries (Jamun)

Solution: Litmus is a pH indicator that is commonly used in laboratories. It is derived from a mixture of different dyes obtained from species of lichens, such as Roccella tinctoria. Litmus solution is purple in color in a neutral state. It turns red in acidic solutions and blue in basic solutions. China rose, beetroot, and blue berries can also act as natural indicators but are not the source of litmus. Therefore, the correct source of litmus is lichen, corresponding to option (c).

7. Neutralisation reaction is a

(a) physical and reversible change.

(b) physical change that cannot be reversed.

(d) chemical change that cannot be reversed.

Solution: A neutralization reaction involves the chemical reaction between an acid and a base, resulting in the formation of a salt and water. This process involves the breaking and formation of chemical bonds, which is characteristic of a chemical change. While the reaction itself is chemical, it is generally considered irreversible under normal conditions. Attempting to reverse the reaction would require specific conditions and reagents to regenerate the original acid and base from the salt and water. Therefore, a neutralization reaction is best described as a chemical change that cannot be easily reversed. This makes option (d) the most appropriate answer.

Common mistakes

Adding water to concentrated acid, which can be dangerous.
Confusing the color changes of indicators in acidic and basic media.
Incorrectly identifying the products of neutralization.
Suggesting inappropriate substances for treating basic soil.

Revision tips

Memorize the safe method for diluting acids.
Create a table of indicators and their color changes in acids and bases.
Understand the chemical reaction behind neutralization.
Review the practical applications discussed in the chapter, like soil treatment.

Practice MCQs

Q1. What is the safe and correct method for preparing a solution of an acid in water?

Q2. What are the typical products formed when an acid and a base react in a neutralization reaction?

Q3. How does turmeric paste, a natural indicator, change color when mixed with an acidic solution?

Q4. What color does phenolphthalein indicator show in a basic solution?

Q5. To improve the quality of soil that has become too basic, what should be added?

Q6. From which natural source is the indicator 'litmus' typically obtained?

Frequently asked questions

What is the safest way to dilute an acid?

The safest way to dilute an acid is to slowly add the acid to water, stirring continuously. Adding water to acid can cause a dangerous exothermic reaction.

What are the products of a neutralization reaction?

A neutralization reaction between an acid and a base always produces a salt and water.

How does turmeric indicate whether a substance is acidic or basic?

Turmeric paste is yellow. It remains yellow in an acidic solution and turns red in a basic solution.

What color does phenolphthalein show in acidic and basic conditions?

Phenolphthalein is colourless in acidic solutions and turns pink in basic solutions.

How can the quality of basic soil be improved for better plant growth?

Basic soil can be improved by adding organic matter, which helps to neutralize the excess base and make the soil more suitable for plants.

Where does the natural indicator litmus come from?

Litmus is a natural dye extracted from lichens.

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