Science · Class 7
Acids, Bases and Salts
Natural and synthetic indicators; neutralisation in daily life.
4 sections15–25 min read6 MCQs · 2 examples
Chapter Overview
Acids taste sour, turn blue litmus red; bases taste bitter, feel soapy, turn red litmus blue. This chapter covers natural indicators, neutralisation, and important salts in daily life.
Acids and Bases
- Acids: HCl in stomach, citric in lemon, acetic in vinegar
- Bases: NaOH (caustic soda), lime water Ca(OH)₂
- Neutral: pH 7 — salt and water from neutralisation
Indicators
- Litmus: red in acid, blue in base
- Turmeric: yellow in acid/neutral, red in base
- China rose (gudhal): dark pink in acid, green in base
- Phenolphthalein: colourless in acid, pink in base
Neutralisation and Salts
- Acid + Base → Salt + Water
- Examples: HCl + NaOH → NaCl + H₂O
- Common salt, baking soda, bleaching powder uses
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Indicator test
Turmeric stain on shirt turns red with soap. Why?
- 1Soap is basic
- 2Turmeric acts as indicator
- 3Base turns turmeric red
Answer
Soap is basic — indicator colour change
Neutralisation
What happens when antacid is taken for acidity?
- 1Antacid is mild base
- 2Neutralises excess HCl in stomach
- 3Forms salt and water, relieves pain
Answer
Neutralisation of stomach acid
Key Points to Remember
- ✓ Strong acids/bases corrosive — handle carefully
- ✓ Acids produce H⁺ in water; bases OH⁻
- ✓ Plants and animals have natural indicators
Exam Tips
- • Test unknown solution with litmus and turmeric
- • Write neutralisation equation for HCl and NaOH
- • List uses of common salt and baking soda
Practice MCQs — Acids, Bases and Salts
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Question 1 of 6Score: 0/0
Acids turn blue litmus: