The vapor pressure of pure, solid pyrene at 25 degree C is given by the variable
ID: 892685 • Letter: T
Question
The vapor pressure of pure, solid pyrene at 25 degree C is given by the variable P_1 atm. The solubility of pyrene in H_2O at 25 degree C is 1.0 Times 10^-4 M, whereas the solubility in ethanol at 25 degree C is greater than 1 Times 10^-4 M. (a) Derive an expression for the vapor pressure of pyrene above a saturated solution in water at 25 degree C (b) If ethanol is added to the saturated aqueous soln, more pyrene dissolves. When equilibrium is reached again, will the vapor pressure of the pyrene above the new solution be greater than, less than, or equal to that in part (a)?Explanation / Answer
a)The vapor pressure of saturated solution of pyrene in water ca n be expressed by Raoult's law.
According to Raoult's law the vvapour pressure of solution P = Xpyrene . P1 + Xwater.Pwater
where X stands for molefraction.
b) When ethanol is added to water total vapor pressure of the solution comes from all three components ,water, ethanol and pyrene. However ethanol being more volatile than pyrene, the vapors are richer in ethanol , thus the vapor pressure of pyrene above new solution is less than that of that in part a, though the solubility increases.
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