Materi XII IPA
A. Balancing redox reactions.
By using the redox reaction method, the equations may either be direc-
Tly in their oxidation number method and ion electron method.
a. Oxidation number method.
Balancing in oxidation number method form :
Suppose the following equation in given the balancing .
KMnO4 + HCl → KCl + MnCl2 + Cl2 + H2O (acid)
Following are steps involved :
Step I : Identify the O.N and write down their chemical changes in separate
equations.
KMnO4 + H Cl → KCl + MnCl2 + Cl2 + H2O
+7 -1 +2 0
Step 2 : Balance separately those atoms of equations which are either oxidised or
Reduxed.
KMnO4 + 2 H Cl → Mn2+ + Cl2 + H2O
Reduxed
Oxidised
Step 3 : Mention electrons used in redox process separately in equations and then
balance them.
K MnO4 + 2 HCl → KCl + MnCl2 + Cl2 + H2O
+7 -2 +2 0 Reduxed 5
Oxidised 2
Step 4 : After balancing the electrons, both equations are added and common spe-
cies as well as coeffisient of reactant and product are eleminated.
2 KMnO4 + HCl → KCl + MnCl2 + 5 Cl2 + H2O
Step 5 : Balancing Oxigen atom and H atom with to add H2O.
2 KMnO4 + 16 HCl → KCl + MnCl2 + 5 Cl2 + 8 H2O
Step 6 : Balancing all atoms.
2 KMnO4 + 16 HCl → 2 KCl + 2 MnCl2 + 5 Cl2 + 8 H2O
Practice Problem :
Balancing the following redox equation using the oxidation number.
1. Cr2O72-(aq) + HNO3(aq) → Cr2+(aq) + NO3- (aq). (acid condition).
2. Cr(OH)3(aq) + ClO3- (aq) → CrO42-(aq) + Cl- (aq). (basic condition).
4. IO3- (aq) + I- (aq) + H+(aq) → I2 (aq) + H2O (aq). (acid condition).
3. I2(aq) + S2O32- (aq) → I- (aq) + S4O62-
4. MnO4- (aq) + C2O42-(aq) → MnO2(aq) + CO2 (g) (acid condition).
5. Cl2 (aq) + IO3- (aq) → Cl- (aq) + IO4- (aq) (basic condition).
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