Question

Liquids A and B form an ideal solution. At 25 °C, the vapor pressure of pure A is 300 torr, and then the vapor pressure of B is

r42 torr. Calculate the mole fraction of B in the solution when both A and B are equal at 25 °C.
A. 0.8716
B. 0.4705
C. 0.7059
D. 0.2941

Answer 1

To calculate the mole fraction of B in the solution, we can use Raoult's law. According to Raoult's law, the vapor pressure of a component in a solution is equal to the vapor pressure of that component in its pure form multiplied by its mole fraction in the solution. Given the vapor pressure of B in the solution and the vapor pressure of pure B, we can calculate the mole fraction of B to be approximately 0.14.

Step-by-step explanation:

To calculate the mole fraction of B in the solution, we can use Raoult's law. According to Raoult's law, the vapor pressure of a component in a solution is equal to the vapor pressure of that component in its pure form multiplied by its mole fraction in the solution. So, for component B:

PB = XB * PºB

where PBis the vapor pressure of component B in the solution, XB is the mole fraction of component B, and PºB is the vapor pressure of pure B.

Given that PB = 42 torr, we can rearrange the equation to solve for XB:

XB = PB / PºB = 42 torr / 300 torr ≈ 0.14 (rounded to two decimal places).