Size vs. Charge of atoms

[drspacheman]

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If you had a semipermeable membrane that separates atoms by both size and charge, which of the two atoms would move with the slowest rate across the membrane?

K+ or Ca2+?

The particular answer to this question, out of TBR chemistry, states that Ca2+ would move with the slowest rate.

However, K+ is a bigger atom. So I was wondering, when comparing size and charge of atoms, does charge play a more prominent role?

 

[cheesier]

If you had a semipermeable membrane that separates atoms by both size and charge, which of the two atoms would move with the slowest rate across the membrane?

K+ or Ca2+?

The particular answer to this question, out of TBR chemistry, states that Ca2+ would move with the slowest rate.

However, K+ is a bigger atom. So I was wondering, when comparing size and charge of atoms, does charge play a more prominent role?

I got curious about the answer and I found this:

http://www.sciencedirect.com/science/article/pii/S0022283665800936

Basically because the charged ion has to pass through a nonpolar layer, the limiting factor is the size of the charge, not the size of the molecule. However it is a crappy question because it gives no info about the membrane so I'm assuming it is nonpolar.

 

[drspacheman]

Good find, very interesting. Yeah the question really sucked they didn't give enough info in the passage about the membrane in question.
Thanks!