Phosopholipids in Salty solutions

[Krazer101]

Homework Statement

Consider a phospholipid bilayer membrane consisting of a mixture of 90% uncharged lipid and 10% singly charged acid lipid. Assume 68 Angstroms surface area per lipid head groups, and assume further that the charged lipids are uniformly distributed and immobile. The membrane is in contact with an aqueous solution of NaCl at 25 degrees celsius. The salt concentration is 100mM.

a.) Calculate the areal charge density of the membrane

b.) Calculate the surface potential of the membrane

Homework Equations

area density = derivative of charge?
Electric field and potential equations

The Attempt at a Solution

I am totally stuck and have no idea where to begin. I was first wondering what to model the membrane as? Should I model the bilayer as concentric spheres? I believe if I use concentric spheres, I can find the potential. I am unsure about the charge density; I don't quite understand how to use percentage of heads that are charged/not for this.

 

[Krazer101]

Anyone know where to start?