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### Topic: Charged Membrane  (Read 1836 times)

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#### podpod

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##### Charged Membrane
« on: October 18, 2015, 08:04:02 AM »
Hi!
I have troubles with the solution of this problem:
Consider a cation transfer membrane with a fixed concentration Cx of sulfonate (SO3-) groups. The membrane is in equilibrium with a solution of a 2-1 salt (CaCl2).
Calculate the Donnan potential between the cation transfer membrane and a 0.02 M CaCl2 solution. The charge density of the membrane is 2.5 meq per g dry membrane. The water sorption of the membrane in 0.01 M CaCl2 is 0.25 g per g dry membrane and the density of the wet membrane is 1.15 g/cm3.

I use (s) and (m) for concentration in solution and in membrane respectively. In order to find the Donnan potential I need C(m)Cl-.

Having C(s)Ca2+ = 0.02M and C(m)Cl- = 0.04M because of 0.02M of CaCl2, I thought to apply a two-equations system to find C(m) of the ions:
{ C(m)Ca * C(m)Cl^2 = C(s)Ca * C(s)Cl^2 ;
2*C(m)Ca = C(m)Cl + Cx }

to do this I need Cx referred to liter, but it is expressed in 2.5 meq/g of dry m. That's my problem: I don't know how I can use the other parameters to have Cx[mol/L].

​thank you very much!!