Question

Prove by writing chemical equations that KMnO4 and K2Cr2O7 can oxidise ferrous sulphate to ferric sulphate in the presence of sulphuric acid.​

Answer 1

Answer:

10 FeSO4 (aq) + 2 KMnO4 (aq) + 8 H2SO4 (aq) → 5 Fe2(SO4)3 (s) + 2 MnSO4 (aq) + K2SO4 (aq) + 8 H2O (l)

6 FeSO4 + K2Cr2O7 + 7 H2SO4 → K2SO4 + 3 Fe2[SO4]3 + Cr2[SO4]3 + 7 H2O

Explanation:

Here, in the first reaction -

reduction half reaction:

8H+ + MnO4^- + 5e- = Mn2+ + 4H2O    (1)

oxidation half reaction:

Fe2+ = Fe3+ + e-   (2)

so, in multiplying 2 with (1) and 10 with (2) we get -

10 FeSO4 (aq) + 2 KMnO4 (aq) + 8 H2SO4 (aq) → 5 Fe2(SO4)3 (s) + 2 MnSO4 (aq) + K2SO4 (aq) + 8 H2O (l)

Here, in the second reaction -

reduction half reaction:

14H+ + Cr2O7^2- + 6e- = Cr3+ + 7H2O    (1)

oxidation half reaction:

Fe2+ = Fe3+ + e-   (2)

so, in multiplying 1 with (1) and 6 with (2) we get -

6 FeSO4 + K2Cr2O7 + 7 H2SO4 → K2SO4 + 3 Fe2[SO4]3 + Cr2[SO4]3 + 7 H2O