At 80°C,pure liquid A has a vapor pressure of 700 mm Hg and pure liquid B has a vapor pressure of 940 mm Hg.What is X_A for a solution of A and B with a normal boiling point of A)0.25 B)0.50 C)0.75 D)A solution of A and B cannot boil at 80°C.

Question

Quizplus · Accepted Answer

We can use Raoult's law to calculate the vapor pressure of the solution at 80°C. Raoult's law states that the partial pressure of a component in a solution is equal to the vapor pressure of the pure component multiplied by its mole fraction in the solution. We are given the vapor pressures of pure A and B at 80°C. Let x be the mole fraction of A and (1-x) be the mole fraction of B in the solution. Using Raoult's law, we get: P_total = x * P_A + (1-x) * P_B Where P_total is the vapor pressure of the solution. At the normal boiling point, the vapor pressure of the solution is equal to atmospheric pressure, which is 760 mm Hg. Thus, we can set up the following equation: 760 = x * 700 + (1-x) * 940 Solving for x, we get x=0.25 Therefore, X_A = 0.25, which means that the solution contains 25% A and 75% B. Thus, the best choice is (C).

At 80°C,pure Liquid a Has a Vapor Pressure of 700