Revision Notes for Class 7 Science Chapter 2: Exploring Substances – Acidic, Basic and Neutral

Condensed revision notes for Class 7 Science Chapter 2: Exploring Substances – Acidic, Basic and Neutral – Curiosity textbook. These Class 7 Science Chapter 2 notes are ideal for quick revision just before exams.

Last Updated: September 23, 2026

• Litmus paper: made from lichen extract. Acids turn blue litmus red; bases turn red litmus blue; neutral substances cause no change to either.
• Natural indicators: turmeric (turns red in base, no change in acid/neutral) and red rose extract (turns red in acid, green in base) can substitute for litmus.
• Olfactory indicators: substances like onion and vanilla extract change smell depending on acid/base exposure — useful when colour can’t be observed.
• Acidic substances (Group A): lemon juice, amla juice, tamarind water, vinegar, orange juice — taste sour due to natural acids (citric acid, tartaric acid, acetic acid).
• Basic substances (Group B): soap solution, baking soda solution, lime water, washing powder solution — often feel soapy and taste bitter.
• Neutral substances (Group C): tap water, sugar solution, salt solution — cause no colour change with any indicator.
• Neutralisation: mixing an acid and a base cancels out (neutralises) each other’s character, moving the result toward neutral — used in treating acidic soil (adding lime), acidic industrial waste, and antacids for excess stomach acid.

More on this chapter: NCERT Solutions for Class 7 Science Chapter 2 | Extra Questions for Class 7 Science Chapter 2 | Class 7 Science Book | Formulas Handbook

Frequently Asked Questions

How can you test whether a substance is acidic, basic, or neutral without tasting it?
Indicators such as litmus paper are used to test substances safely; red litmus turns blue in a basic substance, blue litmus turns red in an acidic substance, and litmus shows no change in a neutral substance.

What happens when an acid and a base are mixed together in the right proportions?
When an acid and a base react together, they neutralise each other, forming salt and water and reducing the acidic or basic strength of the resulting mixture.

Written by Satish

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