# MathBench>Cellular Processes

## 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!