Question

why does the blue color of the copper sulphate turn to pale green when an iron nail is dipped in it for twenty minutes?

Answer 1

When iron nails are kept dipped in copper sulphate solution for about 30 minutes, the blue colour of the aqueous copper sulphate would slowly fade to become green and a brown deposition would be seen on the iron nails.

Why does this happen?

It happens because iron is more reactive than copper, that implies that it is more happy to give away electrons. Talking generally, when a piece of more reactive metal is immersed in an aqueous salt solution of a less reactive metal, a displacement reaction takes place, in which the less reactive metal precipitates out in its original solid form and the more reactive metal forms the aqueous salt solution.

Here, in this case, iron displaces copper to form ferrous sulphate’s aqueous solution(green) and copper(brown flakes) precipitates out.

It can be summed up as the following reaction-

CuSO4(blue)(aq) + Fe(gray)(s) → FeSO4(green)(aq) + Cu(brown)(s)

Answer 2

When Iron nail (Ferrum) is dipped in Copper sulphate (CuSO4) there takes reaction between them and coppersulphate change its color from blue to light green. This shows Iron is more reactive than Copper, it can replace Copper from CuSO4.