Confused about Vapor Pressure again!?

The vapor pressure of water at 20°C is 17.5 torr. A 21.6% solution of the nonvolatile solute ethylene glycol, C2H4(OH)2, in water is prepared. Calculate the change in vapor pressure of the solution to three significant figures.

Answer:
The solution is 21.6 % by mass
This means 21.6 g of ethilene glycol in 100 - 21.6 = 78.4 g of water.
Molecular weight C2H4(OH)2 ) = 62 g/mol
21.6 g / 62 = 0.348 moles
Molecular weight H2O = 18 g/mol
78.4 / 18 = 4.35 moles H2O
mole fraction = 4.35 / 4.35 + 0.348 = 0.926
p (a)= p°(a) Xa = 17.5 x 0.926 = 16.2 torr

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