Question

A cleaned aluminium foil was placed in an aqueous solution of zinc sulphate. When the aluminium foil was taken out of the zinc sulphate after 15 minutes, its surface was found to be coated with a silvery grey deposit. From the above observation what can be concluded?

Answer 1

Hint:
 The above situation is an example of displacement reaction in which one element is displaced by a more reactive element.

Complete step by step solution:
 When a cleaned aluminium foil is placed in an aqueous solution of zinc sulphate and taken out after 15 minutes, its surface is coated with a silvery grey deposit due to displacement of the metal zinc by aluminium as in the aqueous solution of zinc sulphate ions of $Z{n^{2 + }},SO_4^{2 - }$ are found since aluminium is more reactive than zinc it will displace zinc from zinc sulphate to form aluminium sulphate a balanced equation of the above reaction can be written like :
$2A{l_{(s)}} + 3ZnS{O_{4(aq)}} \to 3Z{n_{(s)}} + A{l_2}{(S{O_4})_{3(aq)}}$
Aluminium is a white grey coloured metal and zinc is a blue grey coloured metal. A silvery grey deposit is visible on the surface due to the deposition of aluminium sulphate on the surface formed by displacing zinc from zinc sulphate solution. This reaction is a redox reaction as well because both oxidation and reduction takes place in the reaction. Zinc is reduced from the oxidation state of +2 to an oxidation state of zero which is the pure elemental state and aluminium is oxidized to an oxidation state of +3. Therefore zinc sulphate is an oxidizing agent and aluminium is a reducing agent.

Note:
Reactivity series is the list of all the metals and has enlisted which metal is reactive than whom. Noble metals are placed at the end of the list as they do not react.