chemistry 2 question 3

Question

how many moles of ethylene glycol (C2H6O2) should be added to 25.0 moles of water to make a solution with a vapor pressure of 17.5 torr? the vapor pressure of pure water is 23.8 torr. you can assume that the ethylene glycol vapor pressure is negligible.

Answer 1

P_soln=X_H2OP^o_H2O

Raoult's Law

P_soln=17.5 torr

P^o_H2O=23.8 torr

X_H2O=(mol_water/(mol_water+mol_{ethyleneglycol}))

X_H2O=(25/(25+x))

Therefore:

P_soln=X_H2OP^o_H2O

17.5=(²⁵/_(25+x))23.8

Solve for x, which is moles ethylene glycol

x=9.0 mol