## Taking Nernst for a test drive

Well, that was a lot of work, but we finally have a way of calculating the equilibrium potential based on the concentration gradient of an ion.

Let's give this equation a run for its money. Remember the typical cell? And remember that the cell's membrane is generally only permeable to potassium (K+)? So...

### What is the Nernst potential associated with the potassium ion?

(To make this problem interactive, turn on javascript!)

- I need a hint: This problem is basically plug-and-chug

- ... another hint ... : put the values of [K+]
_{out}and [K+]_{in}into the equation

- ... another hint ... : like this: V = 62 log(5/140)
- ... another hint ... : get your calculator out ! please please please !

#### I think I have the answer: -90 mV

Bet you thought that was going to be harder... Let's try another one

### What is the Nernst potential associated with the sodium ion?

(To make this problem interactive, turn on javascript!)

- plug and chug!: [Na+]
_{out}is 145 and [Na+]_{in}is 10 - ... another hint ... : your calculator is your friend!

#### I think I have the answer: +72 mV

Copyright University of Maryland, 2007

You may link to this site for educational purposes.

Please do not copy without permission

requests/questions/feedback email: mathbench@umd.edu