Question

14H⁺(aq)+Cr₂O₇^2-(aq)+3Ni(s)--->2Cr³⁺(aq)+Ni²⁺(aq)+7H₂O(l)

In the above reaction, a piece of solid nickle is added to a solution of potassium dichromate. Which species is being oxidized and which is being reduced? Write the oxidation and reduction reactions. How many moles of electrons are transferred when 1 mole of potassium dichromate is mixed with 3 mol of nickle?

Answer 1

Ni is oxidized

Cr2O7^2- is reduced

oxidation half reaction                                                       reduction hlaf reaction

Ni(s) -----------. Ni^2+ (aq)                                                Cr2O7^2-(aq) -------->2Cr^3+ (aq)

Ni(s) -----------. Ni^2+ (aq)                                              Cr2O7^2-(aq) -------->2Cr^3+ (aq) +7H2O(l)

Ni(s) -----------. Ni^2+ (aq)                                             Cr2O7^2-(aq)+14H^+(aq) -------->2Cr^3+ (aq) +7H2O(l0

Ni(s) -----------. Ni^2+ (aq) +2e^-                             Cr2O7^2-(aq)+14H^+(aq) +6e^- -------->2Cr^3+ (aq) +7H2O(l)

                                    3Ni(s) -----------. 3Ni^2+ (aq) +6e^-                       

     Cr2O7^2-(aq)+14H^+(aq) +6e^- -------->2Cr^3+ (aq) +7H2O(l)

                --------------------------------------------------------------------------------------------

                  Cr2O7^2-(aq) +3Ni(s) + 14H^+ (aq) -------> 3Ni^2+ (aq) + 2Cr^3+ (aq) + 7H2O(l)

Total 6 electrons are transferred

6 moles of electrons are transferred when 1 mole of potassium dichromate is mixed with 3 mol of nickle