(i)

Rusting

Chemical change because a new substance (rust) different from iron is formed.

(ii)

Burning

Chemical change because the ash cannot be turned back easily into the original material.

(iii)

Filtration

Physical change because the components can be gotten easily.

(iv)

Expansion of copper

Physical change because the original shape of the copper can be gotten easily.

(i)

(ii)

Physical and chemical changes

For a physical change,
1. The original substance can be obtained by a reverse process
2. There is no new substance formed
3. No change in mass occurs
4. The individual components retain their properties
5. There is no heat involved

For a chemical change,
1. The original substance cannot be obtained by reversing the process
2. New substances are formed
3. Change in mass occurs
4. Individual components lose their properties
5. There is heat involved

i)

Differences between a physical change and a chemical change

ii)

Examples of a physical change

1. Dissolving sugar in water
2. Sand and sugar mixture
3. Sulphur and iron filing mixture
4. Melting of candle
5. Melting of ice
6. Expansion of copper
7. Filtration
8. Freezing of water
9. Grinding of chalk
10. Boiling of an egg for five minutes
11. Chewing of meat in the mouth for two minutes
12. Pounding of boiled cassava and plantain together into fufu

Examples of a chemical change

1. Burning wood
2. Reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl)
3. Rusting of iron
4. Cooking of food
5. Fermentation
6. Chewing of piece of bread in the mouth for two minutes

(a)

(b)

(i)

Common salt in water → physical change

(ii)

Burning of charcoal → chemical change

(iii)

Melting of ice → physical change

(iv)

Hydrochloric acid in sodium hydroxide solution → chemical change