Question

Balance a Redox Reaction (Acidic)

ClO3^- (aq)+I2(aq)------->Cl^- (aq)+IO3^-(aq)

Answer 1

1. break the given equation into redox (gain electrons) and oxidation (lost of electrons) equations
oxid (call eq 1): ClO3- --->Cl- and redox (call eq 2): I2--->IO3-

2. balance out the main elements
balance out the Cl: ClO3- --->Cl- and balance the I: I2--->2 IO3-

3. balance the O's with H2O
ClO3- --->Cl- + 3H2O and 6H2O + I2--->2 IO3-

4. balance the hydrogens in H2O with H+
6H+ + ClO3- --->Cl- + 3H2O and 6H2O + I2--->2 IO3- + 12 H+

5. balance the charges on each side of each equation resulting from the previous charged species and the added H+'s using e- (electrons)
6e- + 6H+ + ClO3- --->Cl- + 3H2O and 6H2O + I2--->2 IO3- + 12 H+ +10 e-

6. simplify by adding the two equations together and causing the e-'s to cancel out. you do that by multiplying the indv equations by a scalar to create same # of e-'s in both equations.
in this case, multiply eq 1 by 5 to get:
30e- + 30H+ + 5 ClO3- --->5 Cl- + 15 H2O
and multiply eq 2 by 3 to get 18 H2O + 3 I2--->6 IO3- + 36H+ +30 e-
this makes the e-'s 30 in both eq 1 and 2

7. now do arithmetic to simplify to 5 ClO3- + 3H2O + 3 I2 --> 6H+ + 5 Cl- + 6 IO3- which is your balanced eq.