Class 7 Science

Chapter 5: Acids, Bases and Salts

STAGE 0: Foundation / Basics

Some substances taste sour, some taste bitter, and some are salty.

Based on their nature, substances are grouped as acids, bases, and salts.

STAGE 1: Acids

Acids are substances that taste sour.

Examples of acids:

• Lemon juice – Citric acid
• Vinegar – Acetic acid
• Curd – Lactic acid

Bases

Bases are substances that taste bitter and feel soapy.

Examples of bases:

• Soap
• Baking soda
• Washing soda

Salts

Salts are formed by the reaction of an acid and a base.

Common salt is an example of salt.

Indicators

Indicators help us to identify whether a substance is acidic or basic.

Common indicators:

• Litmus
• Turmeric
• China rose

Litmus test:
Acid → Blue litmus turns red
Base → Red litmus turns blue

STAGE 2: NCERT Textbook Questions & Answers

Q1. What are acids?

Acids are substances that taste sour and turn blue litmus red.

Q2. What are bases?

Bases are substances that taste bitter and turn red litmus blue.

Q3. What is an indicator?

An indicator is a substance that shows whether a solution is acidic or basic.

STAGE 3: Exam-Oriented Questions

Fill in the blanks:

• Lemon juice contains citric acid.
• Soap solution is basic in nature.

Very Short Answer:

Which indicator is obtained from plants?
Answer: Litmus

Quick Revision Points

• Acids taste sour
• Bases taste bitter
• Salts are formed from acids and bases
• Indicators identify acids and bases