What is the coefficient for H2O(l) when the reaction PbO2(s) + I2(s) → Pb2+(aq) + IO3−(aq) is balanced in an acidic aqueous solution?

• A. 4
• B. 1
• C. 2
• D. 3

Answer: (D)

Verified step by step guidance

1. Identify the oxidation states of the elements in the reactants and products to determine which elements are oxidized and reduced. Lead (Pb) in PbO2 is reduced to Pb2+, and iodine (I2) is oxidized to IO3−.
2. Write the half-reactions for the oxidation and reduction processes. For reduction: PbO2(s) → Pb2+(aq). For oxidation: I2(s) → IO3−(aq).
3. Balance each half-reaction for mass and charge. For the reduction half-reaction, add H2O to balance oxygen and H+ to balance hydrogen. For the oxidation half-reaction, add H2O to balance oxygen and H+ to balance hydrogen, then add electrons to balance the charge.
4. Combine the balanced half-reactions, ensuring that the electrons lost in the oxidation half-reaction equal the electrons gained in the reduction half-reaction. This may require multiplying the half-reactions by appropriate coefficients.
5. Count the number of H2O molecules added to balance the oxygen atoms in the combined balanced equation. This will give you the coefficient for H2O(l) in the balanced reaction.