Question

Balance the following oxidation-reduction (redox) reaction and show your work

Cr2O7^2- + C2O4^2- = Cr^3+ + CO2

Answer 1

Cr2O7^2- + C2O4^2- = Cr^3+ + CO2

Step 1)

Oxidation half reaction balancing atom other than O and H

C2O4^2- --- > 2CO2  

Reduction half

Cr2O7^2- ---- > 2Cr³⁺

Step 2

Balancing of Oxygen by using H2O molecule and H by using H+

C₂O₄^2- --- > 2CO₂

Cr₂O₇^2- + 14 H⁺ (aq) --- > 2Cr³⁺ + 7 H₂O (l)

Step 3

Balancing of charge by using electrons

3 [C₂O₄^2- --- > 2CO₂ + 2 e- ]

Cr₂O₇^2- + 14 H⁺ (aq)+ 6 e-   --- > 2Cr³⁺ + 7 H₂O (l)

Balanced reactions

3 C₂O₄^2- --- > 6 CO₂  + 6 e-

Cr₂O₇^2- + 14 H⁺ (aq)+ 6 e-   --- > 2Cr³⁺ + 7 H₂O (l)

Step4

Addition

3 C₂O₄^2- --- > 6 CO₂  + 6 e-

Cr₂O₇^2- + 14 H⁺ (aq)+ 6 e-   --- > 2Cr³⁺ + 7 H₂O (l)

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

3 C₂O₄^2- + Cr₂O₇^2- + 14 H⁺ (aq) --- > 6 CO2 + 2Cr³⁺ + 7 H₂O (l)

The balanced reduction reaction

3 C₂O₄^2- + Cr₂O₇^2- + 14 H⁺ (aq) --- > 6 CO2 + 2Cr³⁺ + 7 H₂O (l)