NCERT Class 7 Science Curiosity: Chapter 2 — Exploring Substances: Acidic, Basic, and Neutral
This chapter, "Substances: Acidic, Basic, and Neutral," from NCERT's Class 7 Science Curiosity textbook, introduces students to the nature of different substances. It begins with an engaging anecdote about a science fair where invisible ink is revealed using a chemical reaction. The chapter then delves into the concept of indicators, focusing on litmus as a key tool. Through Activity 2.1, students are guided to explore the color changes of blue and red litmus paper when exposed to various common substances like lemon juice, soap solution, vinegar, and baking soda solution. The chapter emphasizes observation and recording these changes to classify substances as acidic, basic, or neutral, fostering scientific inquiry and understanding of chemical properties.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 7 |
| Subject | Science |
| Book | Curiosity |
| Chapter | Chapter 2 — Exploring Substances: Acidic, Basic, and Neutral |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 3 minutes |
| Word count | 403 |
Learning outcomes
- Understand the concept of indicators in chemistry.
- Learn how litmus paper changes color in the presence of acids and bases.
- Identify common substances as acidic, basic, or neutral based on litmus tests.
- Develop observational and recording skills through scientific activities.
Vocabulary
| Word | Meaning |
|---|---|
| Indicator | A substance that changes color to indicate the presence of an acid or a base. |
| Litmus | A natural dye used as an indicator, typically obtained from lichens. |
| Acidic | Having the properties of an acid; capable of turning blue litmus red. |
| Basic | Having the properties of a base; capable of turning red litmus blue. |
| Neutral | Neither acidic nor basic. |
| Lime water | A solution of calcium hydroxide in water. |
| Calcium hydroxide | A chemical compound with the formula Ca(OH)₂. |
| Calcium oxide | A chemical compound with the formula CaO, also known as quicklime or burnt lime. |
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Practice questions
- What is an indicator used for in science? Answer: An indicator is used to show whether a substance is acidic, basic, or neutral by changing color.
- How does blue litmus paper behave in an acidic solution? Answer: Blue litmus paper turns red in an acidic solution.
- What is lime water? Answer: Lime water is a solution of calcium hydroxide in water.
- Name two common substances that might be acidic. Answer: Lemon juice and vinegar are common acidic substances.
Frequently asked questions
What is the main purpose of the science fair event described in the chapter?
The science fair was hosted to celebrate National Science Day and engage students with various scientific activities and demonstrations.
What is litmus and how is it used?
Litmus is a natural dye used as an indicator. It changes color in acidic or basic solutions, helping to identify their nature.
What happens to blue litmus paper when dipped in an acidic solution?
Blue litmus paper turns red when dipped in an acidic solution.
What happens to red litmus paper when dipped in a basic solution?
Red litmus paper turns blue when dipped in a basic solution.
How can one prepare lime water?
Lime water is prepared by mixing lime (calcium oxide) in water, letting it settle, and then filtering the liquid.
What is the difference between lime water and lime?
Lime water is a solution of calcium hydroxide in water, while lime (chuna) refers to calcium oxide.
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Important topics
Topics covered
NCERT Class 7 Science — Curiosity — Chapter 2 — Exploring Substances: Acidic, Basic, and Neutral. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.