Class 7 Science Chapter 2: Exploring Substances: Acidic, Basic, and Neutral Important Questions by PW

Identifying acids, bases and neutral substances is an important part of Class 7 Science, but understanding their properties and reactions can be challenging. You may find it difficult to remember how indicators change colour, distinguish between different solutions, interpret the pH scale or explain experiments involving acids and bases. Applying these concepts to everyday examples also requires practice.

Class 7 Science Chapter 2 Important Questions by PW on Exploring Substances: Acidic, Basic, and Neutral help you revise these concepts through 1-mark, 2-mark and 3-mark questions. Practise identifying substances, understanding indicator tests, writing chemical equations and explaining neutralisation reactions to improve your conceptual clarity and prepare for school assessments.

Class 7 Science Chapter 2 Important Questions

Practise the following questions from Exploring Substances: Acidic, Basic, and Neutral. The questions are divided according to their marks to help you prepare for different types of school assessments.

Q1. Define an acid.

Answer: An acid is a substance that turns blue litmus paper red when tested with it. Many common acids are also described as sour, but laboratory substances should never be tasted.

Q2. What colour does red litmus paper turn in a basic solution?

Answer: Red litmus paper turns blue in a basic solution.

Q3. Name one natural indicator.

Answer: Turmeric or red cabbage juice is a natural indicator.

Q4. What is the pH of a neutral solution at room temperature?

Answer: The pH of a neutral solution is 7.

Q5. Which gas is released when an acid reacts with a suitable metal?

Answer: Hydrogen gas is released.

Q6. What is the commonly described taste of a base?

Answer: Bases are commonly described as bitter. However, substances should never be tasted to identify their nature.

Q7. What is formed when an acid reacts with a base?

Answer: Salt and water are generally formed during a neutralisation reaction.

Q8. Give two examples each of acids and bases found in daily life.

Answer:

• Acids: Lemon juice and vinegar.

• Bases: Soap solution and baking soda solution.

Q9. What happens to blue litmus paper when dipped in an acidic solution?

Answer: Blue litmus paper turns red when dipped in an acidic solution. This colour change indicates the presence of an acid.

Q10. How is turmeric paper used to test for the presence of a base?

Answer: Turmeric paper is a natural indicator that remains yellow in acidic and neutral solutions but turns reddish-brown in basic solutions. Therefore, a reddish-brown colour indicates the presence of a base.

Q11. Why are acids and bases described as having different tastes?

Answer: Acids are commonly described as sour, while bases are described as bitter. These are general properties used in textbooks to introduce acids and bases. However, you should never taste an unknown substance to identify it.

Q12. How do acids react with metals? Give an example.

Answer: Acids react with certain metals to produce a salt and hydrogen gas. For example, zinc reacts with hydrochloric acid to form zinc chloride and hydrogen gas.

Q13. What is the significance of the pH scale?

Answer: The pH scale indicates how acidic or basic a solution is.

• A pH below 7 indicates an acidic solution.

• A pH of 7 indicates a neutral solution.

• A pH above 7 indicates a basic solution.

Q14. Describe an experiment to show that acids turn blue litmus paper red.

Answer:

Follow these steps to demonstrate the effect of an acid on blue litmus paper:

1. Take a small amount of lemon juice in a clean container.

2. Dip a strip of blue litmus paper into the lemon juice.

3. Observe the colour change. The blue litmus paper turns red.

Conclusion: The change from blue to red indicates that lemon juice is acidic.

Q15. Explain how you can prepare a natural indicator at home and use it to test substances.

Answer:

Red cabbage juice can be prepared and used as a natural indicator to identify acidic and basic substances.

1. Cut a few red cabbage leaves into small pieces and boil them in water.

2. Allow the mixture to cool and strain it to collect the purple-coloured liquid.

3. Add a few drops of this indicator to different test solutions. It generally turns pink or red in acidic solutions and blue or green in basic solutions.

The colour changes help identify whether a tested substance is acidic or basic.

Class 7 Science Chapter 2 Important Questions PDF

Revise the key concepts from Exploring Substances: Acidic, Basic, and Neutral with the Class 7 Science Chapter 2 Important Questions PDF by PW. 

How Can Class 7 Science Chapter 2 Important Questions by PW Help You?

Practising questions from this chapter helps you revise important concepts and apply them to experiments and everyday examples. These questions can support your preparation in the following ways:

• Revise Acidic and Basic Properties: Recall the common properties of acids, bases and neutral substances.

• Understand Natural Indicators: Learn how turmeric and red cabbage juice help identify different solutions.

• Practise Litmus Tests: Remember the colour changes that occur when litmus paper comes in contact with acidic or basic solutions.

• Strengthen pH Concepts: Understand how the pH scale classifies substances as acidic, basic or neutral.

• Learn Chemical Reactions: Practise writing equations for reactions between acids and metals and between acids and bases.

• Improve Experiment-Based Answers: Prepare clear explanations of simple activities involving indicators and solutions.

• Prepare for Different Mark Formats: Practise 1-mark, 2-mark and 3-mark questions to improve answer-writing skills.

• Build Conceptual Clarity: Connect scientific concepts with familiar substances and everyday examples.

Regular practice of Class 7 Science Chapter 2 Important Questions can help you understand acids, bases, indicators and neutralisation more clearly. Revise the key properties, practise the experiments and attempt questions across different mark formats. This will strengthen your understanding of Exploring Substances: Acidic, Basic, and Neutral and support your school assessment preparation.

Related Resources

• CBSE Class 7 Science Syllabus

• CBSE Class 7 Science Notes

• CBSE Class 7 Science Sample Papers

• CBSE Class 7 Science NCERT Solutions