NCERT Class 7 Science Chapter 2
Exploring Substances: Acidic, Basic and Neutral
This chapter helps CBSE Class 7 students classify everyday substances as acidic, basic, or neutral using indicators. Students perform simple experiments with natural indicators like turmeric and litmus to test household substances such as lemon juice, vinegar, baking soda, and soap. The chapter builds foundational knowledge about acids and bases that is essential for higher-level chemistry.
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Key Terms
- Acid
- A substance that tastes sour, turns blue litmus red, and has a pH less than 7. Examples include lemon juice and vinegar.
- Base
- A substance that tastes bitter, feels slippery, turns red litmus blue, and has a pH greater than 7. Examples include baking soda and soap.
- Neutral Substance
- A substance that is neither acidic nor basic, has a pH of 7, and does not change the colour of litmus paper. Pure water is a common example.
- Indicator
- A substance that changes colour in the presence of an acid or a base, used to identify the nature of a substance. Examples include litmus, turmeric, and China rose extract.
- Litmus
- A natural indicator extracted from lichens that turns red in acidic solutions and blue in basic solutions.
- Neutralisation
- A chemical reaction between an acid and a base that produces salt and water, resulting in a neutral solution.
Frequently Asked Questions
What are acids and bases in Class 7 Science?▾
Acids are substances that taste sour and turn blue litmus red, such as lemon juice and vinegar. Bases are substances that taste bitter and turn red litmus blue, such as baking soda and soap solution.
What is a natural indicator and give two examples?▾
A natural indicator is a substance obtained from plants that changes colour when mixed with an acid or base. Turmeric and litmus are two common natural indicators used in Class 7 experiments.
How can I test if a substance is acidic or basic at home?▾
You can use turmeric paste or red cabbage juice as a natural indicator. Acidic substances turn turmeric yellow-red, while basic substances turn it dark red or brown. Red cabbage juice turns red with acids and green or yellow with bases.
What is neutralisation in Class 7?▾
Neutralisation is a reaction between an acid and a base that cancels out both, producing a salt and water. For example, mixing hydrochloric acid with sodium hydroxide produces sodium chloride (common salt) and water.
What is the difference between acidic, basic, and neutral substances?▾
Acidic substances have a pH below 7 and turn blue litmus red. Basic substances have a pH above 7 and turn red litmus blue. Neutral substances have a pH of exactly 7 and do not change litmus colour.
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