What is the vapor pressure at 20°C of an ideal solution prepared by the addition of 4.60 g of the nonvolatile solute urea,CO(NH₂)₂,to 50.2 g of methanol,CH₃OH? The vapor pressure of pure methanol at 20°C is 89.0 mmHg. A) 4.15 mmHg B) 76.0 mmHg C) 81.5 mmHg D) 84.9 mmHg E) 13.0 mmHg

Question

Quizplus · Accepted Answer

First, we need to find the mole fraction of urea in the solution:

moles of urea = 4.60 g / 60.06 g/mol = 0.0766 mol 
moles of methanol = 50.2 g / 32.04 g/mol = 1.567 mol

x(urea) = 0.0766 / (0.0766 + 1.567) = 0.0467

We can use Raoult's law to find the vapor pressure of the solution:

P = X(methanol) * P°(methanol)

where P°(methanol) is the vapor pressure of pure methanol and X(methanol) is the mole fraction of methanol in the solution.

X(methanol) = 1 - x(urea) = 1 - 0.0467 = 0.9533

P = 0.9533 * 89.0 mmHg = 84.9 mmHg

Therefore, the answer is D.

What Is the Vapor Pressure at 20°C of an Ideal