[slvcs]

Hello   I am kind of lost with this question .

A biological cell is immersed in a 70. mM solution of NaCl at 37°C. The cell's membrane is permeable only to Na+ ions. When the system reaches equilibrium, a potential difference of 91.3 mV is measured between the inside and the outside of the cell, where the inside has the higher (more positive) potential. Calculate [Na+] inside the cell, assuming the amount of Na+ ions transferred is negligible compared to the total amount of Na+ ions in the solution.

Can someone please how to start it ?

 Thanks

[Sev]

Have you heard of Nernst eqn?
Equilibrium potential is 91.3mV (potential that opposes concentration gradient).

E_Na+ = 61log [Na⁺]_out/[Na⁺]_in (61 is 2.303RT/F at 37deg.)
Solve eqn for [Na⁺]_in

[DUDE778]

My class has the exact same question but more of  a practice quesion.
I solved it and got 1.233mM.  It says its wrong.. what did i do wrong?

[Sev]

I solved it and got 1.233mM.  It says its wrong.. what did i do wrong?

Looks like you have just taken log of [Na⁺]_Out.  Nernst eqn is actually log of fraction [o/i]