Question

(a) Tom has painted his metallic key with blue paint. (b) Sam has kept a metal key outside in the rain for a while and found that it rusted. In both cases (a) and (b) there is a change in colour. How will you decide whether (a) and (b) are physical or chemical changes?

Answer 1

Answer:

(a) is a physical change because no new substance with separate properties is formed, the original metal is simply coated in paint.

On the other hand, in b, there is a chemical reaction:

4Fe + 3O2 + 6H2O  -> 4Fe(OH)3

Hence, the second (b) is a chemical change

Explanation: