A solution of copper sulphate cannot be stored in an aluminum vessel. Give a reason.

Displacement reactions

Reactions in which a more reactive metal displaces a less reactive metal from its salt solution are called displacement reactions. The products of a displacement reaction are predicted from the reactivity series in which the metals are arranged in the order of their reactivity with dilute acids.

Therefore, when a more reactive metal comes in contact with the salt solution of a less reactive metal, the less reactive metal is displaced from the solution.

Reaction of aluminium and copper sulphate

Aluminium (Al) is more reactive than copper (Cu). Therefore, when aluminium comes in contact with copper sulphate $\left({\mathrm{CuSO}}_4\right)$ solution, it displaces copper forming aluminium sulphate $\left[{\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3\right]$. Copper is deposited in its elemental form.

The chemical equation for the reaction is:

$2\mathrm{Al}\left(\mathrm{s}\right)+3{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)\to {\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3\left(\mathrm{aq}\right)+3\mathrm{Cu}\left(\mathrm{s}\right)$

If copper sulphate solution is stored in aluminium containers, aluminium displaces copper from the solution because of its high reactivity. Also, aluminium moves into the solution, and the aluminium containers will be spoiled with time.
Therefore, copper sulphate solution is not stored in aluminium containers.