2Hg2+ + 2e- <-----> Hg2 2+ E (volts) = +0.91 Co2+ + 2e- <-----> Co. E( volts) =

Question

2Hg2+ + 2e- <-----> Hg2 2+      E (volts) = +0.91
Co2+   + 2e- <-----> Co.             E( volts) =
-0.28
a)    Determine the cell voltage of a voliatic cell containing of the Co+2 (1M)/Co (s) and the Hg+2 (1M)/Hg2 2+ (1M) redox couples
b)     Use the Nernst equation to determine the cell voltage for a cell using same redox couples as in the previous problem but with the following non-standard concentration: [Hg2+]=0.0013M, [Hg2 2+]=0.15M, [Co2+]=2.1×10^-4M, and 7.50g Co (s). (you will need the balanced net ionic equation to use the Nernst equation)

Explanation / Answer

ANSWER:

Redox reaction

2Hg2+ + Co ---------------> Co2+ + Hg22+

Ecell (cell voltage) = Eocell -0.059 log[oxidised][reduced] n = no of electrons transfered in balanced chemical reaction. Eocell = standard emf of cell (= Eoreduction cell - Eooxidation cell)

(A) Ecell = [0.91 - (-0.28)] - 0.0295 log(1
)

Ecell = 1.19V

(B)  Ecell = [0.91 - (-0.28)] - 0.0295 log([Co2+][Hg22+][Hg2+]2[Co])

= 1.19 - 0.0295 log([2.1 X 10-4][0.15][0.0013]2[0.127]) molar mass of Co 7.58.9

= 0.553V

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