Physical and Chemical Changes

Anaerobic bacteria digest animal waste and produce biogas (Change - A).

The biogas is then burnt as fuel (Change - B). The following statements pertain to these changes. Choose the correct one.

(i) Process - A is a chemical change.

(ii) Process - B is a chemical change.

(iii) Both processes A and B are chemical changes.

(iv) None of these processes is a chemical change.

Explain how painting of an iron gate prevents it from rusting.

Describe how crystals of copper sulphate are prepared.

Explain why burning of wood and cutting it into small piece are considered as two different types of changes.

How would you show that setting of curd is a chemical change?

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

Fill in the blanks in the following statements:

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

(b) The chemical name of baking soda is _________.

(c) Two methods by which rusting of iron can be prevented are _________and

____ ____.

(d) Changes in which only _____ __ properties of a substance change are called physical changes.

(e) Changes in which new substances are formed are called _________changes.

State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook.

(a) Cutting a log of wood into pieces is a chemical change. (True/False)

(b) Formation of manure from leaves is a physical change.

(True/ False)

(c) Iron pipes coated with zinc do not get rusted easily. (True/False)

(d) Iron and rust are the same substances. (True/False)

(e) Condensation of steam is not a chemical change. (True/False)

Classify the changes involved in the following processes as physical or chemical changes:

(a) Photosynthesis

(b) Dissolving sugar in water

(c) Burning of coal

(d) Melting of wax

(e) Beating aluminium to make aluminium foil

(f) Digestion of food