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

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NCERT Solutions PDF Class 7 PDF

This resource provides detailed NCERT Solutions for Class 7 Science, Chapter 5: Acids, Bases and Salts. It covers fundamental concepts such as the differences between acids and bases, their properties, and how they affect indicators like litmus. The solutions explain the nature of common substances, the role of ammonia, and the source and use of litmus as an indicator. A key focus is the process of neutralisation, explained with a practical example involving hydrochloric acid and sodium hydroxide. The chapter also addresses common misconceptions, such as the cause of tooth decay and the behaviour of indicators. These solutions are designed to help students understand the core principles of acids, bases, and salts, reinforcing their learning and aiding in effective exam preparation by clarifying each concept and problem step-by-step.

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Quick info

BoardCBSE
ClassClass 7
SubjectScience
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 5: Acids, Bases and Salts

Chapter summary

Chapter 5 of the Class 7 Science NCERT Solutions focuses on Acids, Bases, and Salts. It elaborates on the distinct characteristics of acids and bases, their tastes, and their effects on litmus. The chapter introduces indicators, explaining how litmus is obtained from lichens and used to identify acidic and basic substances. It also details the process of neutralisation, where acids and bases react to form salt and water, providing a practical example. The exercises cover identifying the nature of substances, verifying the neutrality of distilled water, and understanding the role of indicators and neutralisation in everyday phenomena like tooth decay.

Learning outcomes

  • Understand the key differences between acids and bases.
  • Identify the nature (acidic, basic, or neutral) of various substances.
  • Explain the function and source of litmus as a natural indicator.
  • Describe the process of neutralisation with a practical example.
  • Verify the nature of distilled water using litmus.
  • Recognize common household substances as acidic or basic.

Topics covered

Paper topics

  • Acids
  • Bases
  • Salts
  • Properties of Acids
  • Properties of Bases
  • Indicators
  • Litmus
  • Neutralisation
  • Acidic Nature
  • Basic Nature
  • Neutral Nature
  • Tooth Decay

Important topics

  • Differences between Acids and Bases
  • Litmus as an Indicator
  • The Process of Neutralisation
  • Identifying Acidic and Basic Substances
  • Formation of Salt and Water

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Questions and Solutions

Question 1

State the differences between acids and bases.
Solution: The key differences between acids and bases are as follows:
  1. Taste: Acids typically have a sour taste (e.g., lemon juice, curd), whereas bases have a bitter taste (e.g., baking soda, soap).
  2. Effect on Litmus: Acids turn blue litmus solution red. Bases turn red litmus solution blue.
  3. Examples: Common examples of acids include curd, lemon juice, and vinegar. Common examples of bases include baking soda, soap, and lime water.

Question 2

Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?
Solution: Substances that turn red litmus blue are basic in nature. Since ammonia turns red litmus blue, its nature is basic.

Question 3

Name the source from which litmus solution is obtained. What is the use of this solution?
Solution: Litmus solution is obtained from lichens. It is a natural indicator. Its use is to test whether a solution is acidic or basic. In a neutral solution, litmus has a mauve (purple) colour. When added to an acidic solution, it turns red. When added to a basic solution, it turns blue.

Question 4

Is the distilled water acidic/basic/neutral? How would you verify it?
Solution: Distilled water is neutral by nature. We can verify this using litmus paper. If we test distilled water with both red litmus paper and blue litmus paper, neither will change colour. This indicates that distilled water is neither acidic nor basic, hence it is neutral.

Question 5

Describe the process of neutralisation with the help of an example.
Solution: Neutralisation is a chemical reaction in which an acid and a base react with each other to form salt and water. In this process, the acidic nature of the acid and the basic nature of the base are destroyed, resulting in a neutral solution.

Example: Let's consider the reaction between hydrochloric acid (an acid) and sodium hydroxide (a base).

  1. Take about one-fourth of a test tube filled with dilute hydrochloric acid.
  2. Add a few drops of litmus solution to it. The solution will turn red, indicating it is acidic.
  3. Now, gradually add drops of sodium hydroxide solution one by one to the acidic solution while stirring gently.
  4. Continue adding sodium hydroxide solution drop by drop until the red colour just disappears and the solution turns green (or the colour of the indicator in neutral solution).
  5. At this point, the hydrochloric acid has been neutralised by the sodium hydroxide. The resulting solution is neutral, containing salt (sodium chloride) and water.
The reaction can be represented as:

Acid + Base → Salt + Water

Hydrochloric Acid + Sodium Hydroxide → Sodium Chloride + Water

Question 6

Mark 'T' if the statement is true and 'F' if it is false:

(i) Nitric acid turns red litmus blue. (T/F)

(ii) Sodium hydroxide turns blue litmus red. (T/F)

(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)

(iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)

(v) Tooth decay is caused by the presence of a base. (T/F)

Solution:
  1. Nitric acid turns red litmus blue. (F) Nitric acid is an acid, and acids turn blue litmus red, not red litmus blue.
  2. Sodium hydroxide turns blue litmus red. (F) Sodium hydroxide is a base, and bases turn red litmus blue, not blue litmus red.
  3. Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T) This is the definition of a neutralisation reaction between an acid (hydrochloric acid) and a base (sodium hydroxide).
  4. Indicator is a substance which shows different colours in acidic and basic solutions. (T) This is the correct definition of an indicator.
  5. Tooth decay is caused by the presence of a base. (F) Tooth decay is caused by acids, which are produced by bacteria in the mouth from leftover food particles.

Common mistakes

  • Confusing the colour changes of litmus with acids and bases.
  • Incorrectly identifying the cause of tooth decay (attributing it to bases instead of acids).
  • Misunderstanding the role of indicators.
  • Assuming distilled water has acidic or basic properties.

Revision tips

  • Memorize the characteristic taste and colour changes of litmus for acids and bases.
  • Understand the neutralisation reaction as the core concept for forming salts and water.
  • Review the examples of acids and bases provided in the solutions.
  • Practice identifying the nature of substances based on their reaction with litmus.
  • Focus on the definition and process of neutralisation for exam clarity.

Practice MCQs

Q1. Which of the following is a characteristic taste of acids?

Q2. What happens when ammonia, a base, is added to red litmus solution?

Q3. Litmus solution is obtained from which source?

Q4. What is the nature of distilled water?

Q5. The process where an acid and a base react to destroy each other's nature is called:

Q6. Which of the following statements about indicators is true?

Frequently asked questions

What are the main differences between acids and bases?

Acids typically taste sour and turn blue litmus red, while bases taste bitter and turn red litmus blue. Acids react with bases to form salt and water.

What is litmus and how is it used?

Litmus is a natural indicator extracted from lichens. It is used to test whether a solution is acidic (turns litmus red) or basic (turns litmus blue).

What is the process of neutralisation?

Neutralisation is a chemical reaction where an acid and a base react with each other to produce salt and water, cancelling out each other's acidic and basic properties.

Is distilled water acidic, basic, or neutral?

Distilled water is neutral. It does not change the colour of either red or blue litmus paper, indicating it has neither acidic nor basic properties.

What causes tooth decay?

Tooth decay is caused by acids. When we eat food containing sugars, bacteria in our mouth produce acids, which can damage tooth enamel.

How do these NCERT solutions help in exam preparation?

These solutions provide clear, step-by-step explanations for each question, helping students understand the concepts of acids, bases, and salts thoroughly and revise effectively for their exams.

Important links

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