Using standard reduction potentials, calculate the standard emf for the following reaction: Co(s) + 2Co³⁺(aq) → 3Co²⁺(aq). What is the standard emf of this reaction?

• A. 0.77 V
• B. 0.51 V
• C. 0.28 V
• D. 1.23 V

Answer: (B)

Verified step by step guidance

1. Identify the half-reactions involved in the overall reaction. The given reaction involves the oxidation of Co(s) to Co²⁺(aq) and the reduction of Co³⁺(aq) to Co²⁺(aq).
2. Write the oxidation half-reaction: Co(s) → Co²⁺(aq) + 2e⁻. Determine the standard reduction potential for this half-reaction, which is the reverse of the reduction potential for Co²⁺(aq) to Co(s).
3. Write the reduction half-reaction: Co³⁺(aq) + e⁻ → Co²⁺(aq). Look up the standard reduction potential for this half-reaction in a standard reduction potential table.
4. Calculate the standard emf (E°) of the overall reaction using the formula: E° = E°(reduction) - E°(oxidation). Substitute the standard reduction potentials obtained from the table into this formula.
5. Ensure the stoichiometry of the electrons is balanced in the overall reaction. If necessary, multiply the half-reactions by appropriate coefficients to balance the electrons before calculating the standard emf.