Question

Why can not each metal rear to its own salt (eg.Cu and cuso4)?

Answer 1

Reaction of metal with salt is a displacement reaction. It goes like :

Metal A +salt solution of B=>metal B+salt solution of A .

In this A is more reactive than B .

Since , a metal can not displace it self so it can not react to it's own salt. For e.g. copper (Cu) can not displace it self in Copper Sulphate (CuSo4.)