Suppose you construct the following galvanic cell: Fe(s)|Fe2+(aq)||NAD+(aq)|NADH

Question

Suppose you construct the following galvanic cell:

Fe(s)|Fe2+(aq)||NAD+(aq)|NADH(aq)

Fe2++2e-Fe Eo = -0.44V

NAD++2e-+2H+NADH + H+ Eo’ = -0.320V

(note the different standard states)

A) Calculate the overall cell potential at biochemical standard state. Then, calculate the overall cell potential at pH = 0.

B) What is the maximum amount of electrical work that this galvanic cell can perform?

C) Will the cell generate current at biochemical standard state? At chemical standard state? At T = 4oC, pH = 7? At T = 97 oC, pH = 7? Justify your answers.

D) How many protons can be moved across a membrane from pH 7.5 to pH 6.7 using your freshly charged galvanic cell?

If oxygen is present, the following reaction can occur: H+ + NADH + ½ O2 NAD+ + H2O Given the following standard reduction potential, O2 + 4H+ + 4e- 2 H2O Eo = +1.23V

E) If you start with 1M of NADH, what percent of it becomes oxidized after the reaction above reaches equilibrium (at biochemical standard state)?

F) You run your galvanic cell at concentrations of 1 mM NADH and 1 mM Fe2+. What is the overall cell potential? What are the concentrations of these species at equilibrium?

Explanation / Answer

(a)

The overall cell potential at biochemical standard state is

E cell = E NADH - EFe

= -0.32-(-0.44)

= + 0.12 V

maximum work done = -nFE

here number of electrons tranfer =2

maximum work = - 2 x 96485 x 0.12 V

=23.2 kJ

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