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NCERT Solutions for class 7 Science Acids Bases and salts

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Keywords

Acids: The word acid is derived from Latin word acere which means sour. Example: Lemon juice, orange juice.

Bases: Substance that are bitter in taste and feels soapy on touching are called bases. Example: Detergent and soap

Indicators: These are special substances that are used to test whether a substance is acidic or basic in nature. Example of indicators are Turmeric and litmus.

What are the Properties of Acids

  1. Acids are sour.
  2. Acid can turn blue litmus into red.
  3. Acids can react with metals to produce hydrogen.
  4. Examples of acids are Lemon and Orange.

What are the Properties of Bases

  1. Bases are bitter in taste.
  2. Bases feel soapy when touched.
  3. Bases generally do not react with metal.
  4. Examples of bases are Detergent and Soap.

What are Indicators?

Indicators are the special substances that are used to find the acidic or basic nature of a substance.

Litmus paper

  1. It is the most common indicator used to find the acidic or basic nature of a substance.
  2. It is extracted from lichens.
  3. Litmus papers are generally available in red and blue color.
  4. When litmus is added to acidic solution it turns red.
  5. When litmus is added to basic solution is turns blue.

Turmeric (Natural Indicator)

  1. Turmeric is also a natural indicator.
  2. It turn to deep red when reacts with base.
  3. Its color remains yellow when it reacts with acids.

China rose

  1. China rose in a natural indicator.
  2. It turns acidic solutions to dark pink color.
  3. It turns basic solutions to green color.

What is Neutralisation?

When acid and base reacts with each other, it is known as neutalisation reaction. Salt and water is produced in this reaction and evolution of heat takes place.

Neutralisation in everyday life

Indigestion

  1. Indigestion is caused due to too much presence of acid in our stomach.
  2. Indigestion can be cured by taking antacid such as milk of magnesia.
  3. Milk of magnesia contains magnesium hydroxide, which neturalises the effect of excessive acid in our stomach.

Ant bite

  1. When an ant bites, it injects formic acid in our body.
  2. The effect of this acid can be cured by rubbing moist baking soda or otherwise called sodium hydrogencarbonate.

Soil Treatment

  1. When excessive chemical fertilizers are used in fields, it makes the soil acidic.
  2. To neturalise the acidic nature of soil, we can use quick lime or calcium oxide.

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