Worksheet: Balancing Redox Reactions (Half-equation method)

The half-equation method separates the oxidation and reduction of a redox reaction in half reactions. Overall scheme for the half reaction method:

Step 1: Split reaction into half-reactions (reduction and oxidation)

Step 2: Balance the charge or oxidation number with electrons

Step 3: Balance O by adding H2O

Step 4: Balance H by adding H+

Step 5: Multiply by some integer to make electrons (lost) = electrons (gained)

Step 6: Add half equations and cancel substances on both sides

Step 7: (only in basic solution): add OH- and cancel H20

Step 8: Check atom balance and charge balance on both sides of the equation!!!!

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Complete and balance the following redox reactions (skeleton equations) using the half-equation method:

1. Zn(s) + H+(aq) ==> Zn2+ + H2(g) (acidic solution)

______________________________________________________ (reduction)

______________________________________________________ (oxidation)

______________________________________________________ (overall)

 

2. I-(aq) + NO2-(aq) ==> I2 (s) + NO (g) (acidic solution)

______________________________________________________ (reduction)

______________________________________________________ (oxidation)

______________________________________________________ (overall)

3. MnO4-(aq) + Cl- (aq) ==> Mn2+(aq) + Cl2(g) (acidic solution)

______________________________________________________ (reduction)

______________________________________________________ (oxidation)

______________________________________________________ (overall)

 

Do same reaction in basic solution:

______________________________________________________ (overall)

 

4. Br2(l) ==> BrO3-(aq) + Br-(aq) (basic solution)

______________________________________________________ (reduction)

______________________________________________________ (oxidation)

______________________________________________________ (overall)

 

5. CrO4- + S2- ===> Cr3+ + SO42- (acidic solution)

______________________________________________________ (reduction)

______________________________________________________ (oxidation)

______________________________________________________ (overall)

 

6. H2O2 + NO2- ===> H2O + NO3- (acidic solution)

______________________________________________________ (reduction)

______________________________________________________ (oxidation)

______________________________________________________ (overall)