Question

add nail in CuSo4 solution.the colour of CuSo4 disappears why?

Answer 1

An iron nail displaces the Cu from the copper sulphate solution. As a result The colour of CuSO4 disappears.
Fe+CuSO4-FeSO4+Cu. Because copper is less reactive than iron.

Answer 2

Answer :

When the iron nail is added or dipped in the solution of copper sulfate the color of the copper sulfate solution is changes because iron that is most reactive metal than the copper, it displaces the copper form the copper sulfate solution and forms iron sulfate.

The balanced chemical reaction will be,

$Fe(s)+CuSO_4(aq)\rightarrow FeSO_4(aq)+Cu(s)$

It is a single disparagement reaction in which the the most reactive element displaces the less reactive element.

By the stoichiometry, 1 mole of iron react with the 1 mole of copper sulfate to give 1 mole of iron sulfate and 1 mole of copper.