Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
202 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 19
c. I 2 (s) ϩ HClO(aq) 0 IO 3
Ϫ (aq) ϩ Cl Ϫ (aq) (in acid solution)
d. MnO 4
2Ϫ (aq) 0 MnO 4
Ϫ (aq) ϩ MnO 2 (s) (in acid solution)
19.3 Half-Reactions
The oxidation process and the reduction process of a redox reaction
can each be expressed as a half-reaction. For example, consider the
unbalanced equation for the formation of aluminum bromide.
Al ϩ Br 2 0 AlBr 3
The oxidation half-reaction shows the loss of electrons by
aluminum.
Al 0 Al 3ϩ ϩ 3e Ϫ
The reduction half-reaction shows the gain of electrons by bromine.
Br 2 ϩ 2e Ϫ 0 2Br Ϫ
You can use half-reactions to balance a redox equation by following
these five steps.
Step 1 Write the net ionic equation for the reaction, omitting spectator ions.
Step 2 Write the oxidation and reduction half-reactions for the net
ionic equation.
Step 3 Balance the atoms and charges in each half-reaction.
Step 4 Adjust the coefficients so that the number of electrons lost
in oxidation equals the number of electrons gained in reduction.
Step 5 Add the balanced half-reactions and return spectator ions.
Example Problem 19-4
Balancing a Redox Equation by Half-Reactions
Use the half-reaction method to balance this redox equation.
K 2 Cr 2 O 7 (aq) ϩ HCl(aq) 0 CrCl 3 (aq) ϩ KCl(aq) ϩ Cl 2 (g)
Step 1 The strong acid HCl is a reactant, and the reaction occurs in
acid solution. The four dissolved compounds exist as ions in solution. Some of the ions are neither oxidized nor reduced in the
reaction. These ions can be removed from the equation. In this reaction, the ions to be removed are the potassium and hydrogen ions, as
202 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 19
c. I 2 (s) ϩ HClO(aq) 0 IO 3
Ϫ (aq) ϩ Cl Ϫ (aq) (in acid solution)
d. MnO 4
2Ϫ (aq) 0 MnO 4
Ϫ (aq) ϩ MnO 2 (s) (in acid solution)
19.3 Half-Reactions
The oxidation process and the reduction process of a redox reaction
can each be expressed as a half-reaction. For example, consider the
unbalanced equation for the formation of aluminum bromide.
Al ϩ Br 2 0 AlBr 3
The oxidation half-reaction shows the loss of electrons by
aluminum.
Al 0 Al 3ϩ ϩ 3e Ϫ
The reduction half-reaction shows the gain of electrons by bromine.
Br 2 ϩ 2e Ϫ 0 2Br Ϫ
You can use half-reactions to balance a redox equation by following
these five steps.
Step 1 Write the net ionic equation for the reaction, omitting spectator ions.
Step 2 Write the oxidation and reduction half-reactions for the net
ionic equation.
Step 3 Balance the atoms and charges in each half-reaction.
Step 4 Adjust the coefficients so that the number of electrons lost
in oxidation equals the number of electrons gained in reduction.
Step 5 Add the balanced half-reactions and return spectator ions.
Example Problem 19-4
Balancing a Redox Equation by Half-Reactions
Use the half-reaction method to balance this redox equation.
K 2 Cr 2 O 7 (aq) ϩ HCl(aq) 0 CrCl 3 (aq) ϩ KCl(aq) ϩ Cl 2 (g)
Step 1 The strong acid HCl is a reactant, and the reaction occurs in
acid solution. The four dissolved compounds exist as ions in solution. Some of the ions are neither oxidized nor reduced in the
reaction. These ions can be removed from the equation. In this reaction, the ions to be removed are the potassium and hydrogen ions, as