Focus Exercise 6.61

[Stella Nguyen 1J]

Hi everyone!

I was a little confused about this problem, and I was wondering if you guys could elaborate on the conceptual aspect of problems like these?

6.61: In a neuron (a nerve cell), the concentration of K+ ions inside the cell is about 20–30 times as great as that outside. What potential difference between the inside and the outside of the cell would you expect to measure if the difference is due only to the imbalance of potassium ions?

Thank you!

[Ayesha Aslam-Mir 3C]

Hi Stella!

Conceptually, neurons send off signals based on the strength of the difference in charge of ions inside and outside the cell. In terms of chemistry, we're only looking at the potential based on the potassium ions to cause a reaction. We can assume that, since we are only looking at potassium on either end, the standard potential is 0 volts. if our potential is zero, we can use the Nernst equation to solve for the actual potential difference. We can use 20 to 30 as the concentrations in and out of the cell (with out as our product and in as our reactant) since the problem tells us this!

Essentially, it's a little difficult to grasp at first since we aren't looking at a "typical" battery, but you'd treat the potassium in and out of the cell as electrodes, or different stages of the reaction, as the ion concentrations vary. Hope that helps a bit!

[Leyla Anwar 3B]

For this problem, how do you calculate the n? The solutions says that it is 1 but I'm unsure of how that was derived.