Parathion is an organophosphate pesticide with an octanol-water partition coeffi

Question

Parathion is an organophosphate pesticide with an octanol-water partition coefficient of 6456. Parathion is placed in a separatory funnel with water and octanol and shaken. The concentration of it in octanol is found to be 1.1 x 10-2 M. Assume simple equilibrium approaches are sufficient for this problem.

a) What is the parathion concentration in water?

b) A second organophosphate pesticide does not have a listed octanol-water partition coefficient, but you know that if it is added to the separatory funnel, 7.2 x 10-3 % of the pesticide ends up in the aqueous phase. What is the octanol-water partition coefficient for the second pesticide?

Explanation / Answer

a)   Particion coeff Kd = [ Solute in octanol] /[solute in water]

      6456 =   1.1 x 10^ -2 / [solute in water]

[solute in water] = 1.704 x 10^ -6 M

b) Kd =   Percent in octanal / percent in water = (100 - 0.0072) / 0.0072 = 13888

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