Balance the reaction below in acidic aqueous solution, using the oxidation number method. In the balanced equation, what is the coefficient of Fe²⁺?
ClO₃^- + Fe²⁺ → Cl^- + Fe³⁺

Question

Quizplus · Accepted Answer

1) Assign oxidation numbers to all atoms: 
ClOS1U1B13S1U1B0S1U1P1-S1S1P0 + FeS1U1P12+S1S1P0 → ClS1U1P1-S1S1P0 + FeS1U1P13+S1S1P0 
+1 -2 +6 -2 -1 0 -2 -2 +2 +6 0 0 0 +2 +0 → 
-1 -2 +6 -2 -1 0 -2 +6 -2 +6 0 0 0 +2 +0

2) Identify the atoms undergoing oxidation and reduction:
Fe is oxidized from +2 to +3 (loses electrons)
Cl is reduced from +7 to -1 (gains electrons)

3) Balance the atoms undergoing oxidation and reduction:
ClOS1U1B13S1U1B0S1U1P1-S1S1P0 + 2FeS1U1P12+S1S1P0 → ClS1U1P1-S1S1P0 + 2FeS1U1P13+S1S1P0

4) Balance the oxygen atoms with water:
ClOS1U1B13S1U1B0S1U1P1-S1S1P0 + 2FeS1U1P12+S1S1P0 → ClS1U1P1-S1S1P0 + 2FeS1U1P13+S1S1P0 + 6H2O

5) Balance the hydrogen atoms with H+ ions:
ClOS1U1B13S1U1B0S1U1P1-S1S1P0 + 2FeS1U1P12+S1S1P0 + 14H+ → ClS1U1P1-S1S1P0 + 2FeS1U1P13+S1S1P0 + 6H2O

6) Balance the charge with additional H+ ions:
ClOS1U1B13S1U1B0S1U1P1-S1S1P0 + 2FeS1U1P12+S1S1P0 + 14H+ → ClS1U1P1-S1S1P0 + 2FeS1U1P13+S1S1P0 + 6H2O

7) Check that all atoms are balanced and simplify the formula:
ClO3- + FeS2 → Cl- + Fe2(SO4)3

The coefficient for FeS1U1P12+S1S1P0 is 2, and the coefficient for S1S1P0 is 3, for a total coefficient of 6. Therefore, the answer is B.

Balance the Reaction Below in Acidic Aqueous Solution, Using the Oxidation