Download Oxidation-Reduction Reaction Worksheet

Balancing Redox Reactions
Name _____________________________
Date __________
Balance the following oxidation reduction reactions:
1. MnO4-(aq) + H2S(g) --- S(s) + Mn2+(aq)
Determine the oxidation numbers and which element is reduced/oxidized:
Element
Oxidation
Oxidation Number
Reaction
Number Before
After
Type
Mn
H
Not applicable here
S
O
Not applicable here
1. Write two half-reaction equations (oxidation; reduction):
Oxy
Red
2. For each ½ equation, make sure the atoms are balanced on both sides
a. For each ½ equation, balance the oxygen (if necessary) by adding H2O molecules
to one side
b. For each ½ equation, balance hydrogen (if necessary) by adding H+ ions
3. Balance the charge for each ½ equation; electrons on the left for reduction reactions and
on the right in oxidation reactions (if you have +2 on one side, then you need +2 on the
other)
4. If necessary, multiply the equations by an integer so that the number of electrons is the
same in both.
5. Add the half-reactions and cancel the electrons; cancel out any other common terms that
appear on both sides.
2. Cr2O72- + Fe2+ ---> Cr3+ + Fe3+
Element
Oxidation
Oxidation
Number Before
Number After
Cr
Fe
Not applicable here
O
Step 1
Step 2.
Step 2a.
Step 2b.
Step 3.
Step 4.
Step 5.
Reaction
Type
3. Zn + NO3- ---> Zn2+ + NO2
Element
Oxidation
Number Before
Zn
N
O
Step 1
Step 2.
Step 2a.
Step 2b.
Step 3.
Step 4.
Step 5.
Oxidation
Number After
Reaction Type
4. BrO- ---> Br- + BrO3- (this is called a “disproportionation” reaction; the same element is
both oxidized and reduced)
Element
Oxidation
Oxidation
Reaction Type
Number Before Number After
Br
Br
O
Step 1
Step 2.
Step 2a.
Step 2b.
Step 3.
Step 4.
Step 5.
5. H2O2 + I- + H+ ---> H2O + I2
Element
Oxidation
Number Before
I
H
O
(careful!)
Step 1
Step 2.
Step 2a.
Step 2b.
Step 3.
Step 4.
Step 5.
Oxidation
Number After
Reaction
Type
Exercise 2 – converting reaction to Basic solution
Use your answers for reactions 1, 2, and 3 to convert to a basic (not acidic) solution.
Re-write your answer to reaction 1:
a. Now add enough OH- ions to cancel the H+ ions (add OH- to both sides):
b. Convert all H+ + OH- => H2O molecules
c. Cancel like terms that appear on both sides of the reaction (for example, if there are 3H2O
molecules on the left and 1 H2O molecule on the right, you should end up with only 2 H2O
molecules on the left):
Your answer to Reaction 2:
a.
b.
c.
Your answer to Reaction 3:
a.
b.
c.