Question

Balance the following reactions. (a) Cr2O7 2―(aq) + SO3 ―2 (aq) →Cr+3 (aq) + SO4 ―2 (aq) (Oxidation number method, in acidic medium) (b) MnO4 ― (aq) + I― (aq) → MnO2 (s) + I2 (s) (ion-electron method, in basic medium)

Answer 1

(a) Cr2O7^2- = 2Cr^3+

Cr2O7^2- + 6e- + 14H+ = 2Cr^3+ + 7H2O

SO3^2- + H2O = SO4^2- +2H+ + 2e-]×3

or, the overall reaction is

Cr2O7^2- +3SO3^2- +8H+ = 2Cr3+ 3SO4^2- + 4H2O

(b)

MnO4- +5e- + 8H+ -> Mn2+ + 4H2O]×2

2I- -> I2 + 2e-]×5

the overall reaction is

2MnO4- + 10I- + 16H+ = 2Mn2+ +5 I2 + 8H2O