In the complete process of "simple" diffusion of a sub stance S across a membrane...

In the complete process of "simple" diffusion of a sub stance S across a membrane from side 1 to side 2, S first "jumps" into the membrane from the solution at side 1, then diffuses across the membrane interior, and finally "jumps" from the membrane at side 2 into the aqueous solution:

For a symmetric membrane, the rate coefficients for “jump ing” into and out of the membrane are the same at both surfaces, as indicated. At time zero, (S) is added to the solution on side 1. The area of the membrane is A.

a. Give the rate law for the initial rate of appearance of (S) on side 2, taking k1 as the rate-limiting step. Express the rate as

where N2 is the number of moles of (S) on side 2 and A is the area.

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b. Give the rate law for the initial rate of appearance of (S) on side 2, taking k2 as the rate-limiting step. Again, express the rate as

Your equation should contain the concentration of (S) on side 1 as the only concentration term.

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c. Experimentally, you can determine the initial rate of appearance of S on side 2 as a function of the initial concentration of S added to side 1. Using this type of kinetic data alone, can you deduce which step (k1 or k2,) is rate limiting? Explain briefly.

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d. Suppose the membrane surfaces bear a net negative charge and that S is positively charged. What effect, if any, would decreasing the electrolyte concentration have on the initial rate of transport of S across the mem brane? Briefly explain your answer.