What is the standard cell potential for the following reaction?

Question

Cr3+(aq) + 3e- Cr(s); Eo = -0.74V

Pb2+(aq) + 2e- Pb(s); Eo = -0.13V

What is the standard cell potential for the following reaction?

2Cr(s) + 3Pb2+ 3Pb(s) + 2Cr3+(aq)

a. –0.61V

b. –0.87V

c. 1.83 V

d. 0.87 V

e. 0.61 V

Answer 1

3Pb²⁺(aq) + 6e- ==> 3Pb(s) ... reduction half reaction

2Cr(s) ==> 2Cr³⁺(aq) + 6e- ... oxidation half reaction

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3Pb²⁺(aq) + 2Cr(s) ==> 3Pb(s) + 2Cr³⁺(aq) ... redox reaction

Eºcell = -0.13 V + 0.74 V = +0.61 V (Answer e)