Notes of Ch 5 Acid, Bases and Salts Class 7th Science

Study Material and Notes of Ch 5 Acid, Bases and Salts Class 7th Science

  • Acids and Bases
  • Indicators
  • Neutral Substances
  • Neutralisation

Acids and Bases


→ Acids are sour in taste.

→ Substances that are sour to taste are acidic in nature.
Examples: Curd, lemon juice, orange juice, vinegar etc.


→ Bases are bitter to taste and soapy in touch.

→ Those substances that are bitter to taste and soapy to touch are basic in nature.
Examples: Baking soda, antacids, caustic lime etc.


• Chemicals that are used to check acidic or basic nature of substances are called indicators.

→ The indicators indicators change their colour when added to a solution containing an acidic or a basic substance.

Natural Indicators

→ Turmeric, litmus, china rose petals (Gudhal), etc. are some of the naturally occurring indicators

→ One of the most commonly used indicators is litmus solution (a natural indicator).

• Acids turn blue litmus paper to red and bases turn red litmus paper to blue.

→ Turmeric paste and China rose are also natural indicators.

China rose indicator becomes dark pink when an acidic substance is added to it and turns to green when a basic substance is added to it.

→ Turmeric paste remains yellow in acidic solutions but turns to red in basic solutions.

Neutral Substances

→ Substances that are neither acidic nor basic in nature are called neutral substances.

→ Neutral substances do not affect the colour of indicators.


→ When an acid is mixed with a base, they neutralize the effect of each other. This reaction is known as neutralization reaction.

→ Water and salt are produced as products during the neutralization reaction.

→ Heat is also produced during the neutralization reaction.
Acid + Base → Salt + Water + Heat

→ The salt produced during neutralization reactions can be acidic, basic, or neutral in nature.

Ant Sting

→ Ant sting contains formic acid. The effect of this acid is neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution that contains zinc carbonate.


→ Milk of Magnesia (magnesium hydroxide) is an antacid used to neutralise the effect of the acid produced in our stomach.

Soil treatment Soil treatment

→ Excessive use of chemical fertilisers makes the soil acidic.

→ Plants do not grow well on acidic or basic soil.

→ When the soil is too acidic, it basic is treated with bases like quick lime (calcium oxide) or slaked lime (calcium hydroxide). If the soil is basic, organic matter is added to it.

Factory wastes

The wastes of many factories contain acids which are neutralised by adding basic substances.

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