Question

Write balanced net ionic equations for the following reactions in basic solution:

H2O2(aq)+Cr2O2−7(aq)⟶O2(g)+Cr3+(aq)

Express your answer as a balanced net ionic equation. Identify all of the phases in your answer.

Answer 1

First, define the “ACIDIC” solution/conditions as H+ presence and

Basic solution implies OH- once it is balanced.

Also; note that ALL species must be balanced, as well as charges

Typical steps:

1) split half redox cells

2) balance atoms other than O,H

3) balance O by adding H2O

4) balance H by adding H+

5) balance charge by adding e-

6) balance e- by multiplying by the Greatest common divisor

7) Add both equations

8) simplify repeating elements, H+, H2O, and e- typically

9) add OH- if we need basic media, otherwise this is done.

10) Simplify again

H2O2(aq)+Cr2O2−7(aq)⟶O2(g)+Cr3+(aq)

H2O2 = O2

Cr2O7-2 = Cr+3

balance Cr

H2O2 = O2

Cr2O7-2 = 2Cr+3

balance O

H2O2 = O2

Cr2O7-2 = 2Cr+3 + 7H2O

balance H+

H2O2 = O2 + 2H+

14H+ + Cr2O7-2 = 2Cr+3 + 7H2O

balance charge

H2O2 = O2 + 2H+ + 2e-

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

balance e-

3H2O2 = 3O2 + 6H+ + 6e-

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

add all

3H2O2 + 6e- + 14H+ + Cr2O7-2 = 2Cr+3 + 7H2O + 3O2 + 6H+ + 6e-

cancel common terms

3H2O2 + 8H+ + Cr2O7-2 = 2Cr+3 + 7H2O + 3O2

add OH- to balance in basic

3H2O2 + 8H2O + Cr2O7-2 = 2Cr+3 + 3O2 + 8OH-

this is now balanced

add phases

3H2O2(aq) + H2O(l) + Cr2O7-2(aq) = 2Cr+3(aq) + 3O2(aq) + 8OH-(aq)