Question

what is the reason why aqueous solution of FeSO4 are freshly prepared when required for use?

Answer 1

Answer:

(Reason being half filled orbitals being more stable than partial filled). Hence the need to prepare fresh FeSO4 (Fe2+) which can get oxidised to Fe3+ and hence reduce NO3- to NO. [Note: An old prepared FeSO4 sol wil have Fe3+ which wont give the same reaction and wont be able to reduce NO3-].

Answer 2

Answer:

FeSO4 is freshly prepared because if it is left for time Fe may get oxidised with atmospheric oxygen and form any of iron oxide like ferrous oxide or ferric oxide .

And the solution will no more contain pure FeSO4 hence won’t give the desired result after the experiment