Question

Calculate the vapor pressure (in torr) at 298 K in a solution prepared by dissolving 42.4 g of the non-volatile non-electrolye urea {CO(NH2)2} in 195 g of ethanol. The vapor pressure of ethanol at 298 K is 58.9 torr. Give your answer to 2 decimal places.

Answer 1

The vapor pressure at 298 K for this solution is 50,49 Torr.

Step-by-step explanation:

We have to apply Raoult's law to solve this which its formula is:

P pure sv° - P sl = P pure sv° . X (molar fraction)

ΔP = P pure sv° . X (molar fraction)

58,9 Torr - P sl = 58,9 Torr . X

Molar mass urea CO(NH2)2: 60,06 g/m

Molar mass ethanol: 46,07 g/m

Moles for urea: 42,4 g / 60,06 g/m = 0,705 moles

Moles for ethanol: 195 g / 46,06 g/m = 4,233 moles

X (molar fraction): moles from solute / moles from solute + moles from solvent

X (molar fraction): 0,705 / 0,705 + 4,233 = 0,142

58,9 Torr - P sl = 58.9 Torr . 0,142

58,9 Torr - 8,40 Torr = P sl

50,49 Torr = P sl