Estimating a membrane potential

Estimate the equilibrium membrane potential of a cell at 298 K by using the fact that the concentration of K+ inside the cell is about 20 times that on the outside. Repeat the calculation, this time using the fact that the concentration of Na+ outside the cell is about 10 times that on the inside. 

Strategy Because the cell is at equilibrium, set AG = 0 in eqn 5.8 and, after rearrangement, write 

648 X 10 C mol- and the positive sign denotes that the outside has the lower potential. 

Overall Gibbs energy of transfer of an Ion across a biological membrane 

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