Question

Acetone, C_3H_6O, and ethyl acetate, C_4H_8 O₂, are organic liquids often used as solvents. At 30° C, the vapor pressure of acetone is 285 mm Hg and the vapor pressure of ethyl acetate is 118mm Hg.Part A Acetone AWhat is the vapor pressure (in mm Hg) at 30° C of a solution prepared by dissolving 35.0 g of acetone in 20.0 g of ethyl acetate?P vapor= _____ mmHg

Answer 1

The vapor pressure of a solution prepared by dissolving 35.0 g of acetone in 20.0 g of ethyl acetate at 30°C is 241 mm Hg.

In this case, we're dealing with a two-component liquid system that observes Raoult's Law. According to Raoult's Law, the partial vapor pressure of each component in an ideal mixture is equivalent to the vapor pressure of the pure component multiplied by its mole fraction in the mixture.

The first step is to determine the mole fractions of each component. The molecular weight of acetone is 58.08 g/mol and for ethyl acetate it's 88.11 g/mol. Thus, we have:

moles of acetone = 35.0 g / 58.08 g/mol = 0.602 moles

moles of ethyl acetate = 20.0 g / 88.11 g/mol = 0.227 moles

Now, the mole fraction of acetone (χacetone) = moles of acetone / total moles = 0.602 / (0.602 + 0.227) = 0.726

Using Raoult's law, the vapour pressure of the solution at 30°C

(Ptotal) = vapor pressure of pure acetone * χacetone + vapor pressure of pure ethyl acetate * (1 - χacetone) = (285 mm Hg * 0.726) + (118 mm Hg * (1 - 0.726)) = 241 mm Hg