NCERT Class VII Science Solutions: Chapter 6-Physical and Chemical Changes Part 2

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Question 3:

Fill in the blanks in the following statements:

  1. When carbon dioxide is passed through lime water, it turns milky due to the formation of _________.

  2. The chemical name of baking soda is _________.

  3. Two methods by which rusting of iron can be prevented are _________ and _________.

  4. Changes in which only _________ properties of a substance change are called physical changes.

  5. Changes in which new substances are formed are called _________ changes.

Answer:

  1. When carbon dioxide is passed through lime water, it turns milky due to the formation of Calcium carbonate (CaCO3).

As showing in images is a result for Calcium carbonate (CaCO …

Calcium Carbonate (CaCO3)

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  1. The chemical name of baking soda is Sodium bicarbonate (NaHCO3).

As showing in images is a Sodium bicarbonate (NaHCO3).

Sodium Bicarbonate (NaHCO3)

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  1. Two methods by which rusting of iron can be prevented are greasing and galvanization.

As showing in images is a greasing and galvanization.

Greasing and Galvanization

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  1. Changes in which only physical properties of a substance change are called physical changes.

  2. Changes in which new substances are formed are called chemical changes.

Question 4:

When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.

Answer:

This a chemical change as new products are formed.

Baking soda + Lemon juice ------------> Salt + Carbon dioxide + Water

When acid react with carbonates, salt is formed releasing carbon dioxide and water.