Calculate Standard Potential and Equilibrium Constant

Question

The standard potentials for the reduction of nicotinamide adenine dinucleotide (NAD⁺) and oxaloacetate (reactants in the multistep metabolism of glucose) are as follows:

Oxaloacetate^2- (aq) + 2H⁺(aq) + 2e^-(aq) malate^2- (aq)  E°= –0.166 V

NAD⁺(aq) + 2H⁺(aq) + 2e^- NADH(aq) + H⁺(aq)  E° = –0.330 V

A. Calculate the standard potential for the following reaction:

Oxaloacetate^2- (aq) + NADH(aq) + H⁺(aq)malate^2- (aq) + NAD⁺(aq)

B.Calculate the equilibrium constant at 298.15 K for the reaction.

Answer 1

Part (a)

From the lefthand side of the reaction - Oxaloacetate^2- (aq) + NADH(aq) + H⁺(aq)malate^2- (aq) + NAD⁺(aq), you can identify the fact that oxaloacetate is being reduced (gains electrons) and NADH is oxidized (donates electrons).

An easy way to identify this - Oxaloacetate^2- appears on the lefthand side, while NADH appears on the lefthand side as well -- thus being "reversed" from the half reaction (NAD⁺(aq) + 2H⁺(aq) + 2e^- NADH(aq) + H⁺(aq) ).

Use the formula E0cell=E0red−E0oxid to calculate the standard potential:

E0cell = –0.166 V - (–0.330 V) = 0.164 V

Happy to go over the answer to part (b); please shoot me a message set up a session!