Raoults law can be used to determine the molar mass of an un

Raoult\'s law can be used to determine the molar mass of an unknown substance based on the vapor pressure of a solution. This problem will walk you through the steps required. A chemist wants to determine the molar mass of a naturally occurring substance isolated from spearmint. She adds 5.131 g of this substance to 25.00 g of acetone (C3H,O: molar mass 58.08 g/moll. The vapor pressure of the solution is determined to be 0.2444 atmat 25°C. If the vapor pressure of pure acetone at this temperature is 0.2630 atm, what is the mole fraction of the solvent in this solution Give your answer to four significant digits. olvent

Solution

Vapour pressure of pure acetone p0 = 0.2630 atm

Vapour pressure of soluntion p = 0.2444 atm

According to Raoult\'s law,

P0 - P/P0 = mole fraction of solute

(0.2630 - 0.2444)/0.2630 = mole fraction of solute

0.07072 = mole fraction of Solute

mole fraction of solvent = 1 - mole fraction of solute

mole fraction of solvent = 1 - 0.07072 = 0.9293

mole fraction of solute = number of moles of solute/total number of moles of solution

0.07072 = (5.131/M)/((5.131/m)+(25/58.08))

Molar mass of solute = 156.6365 g/mol

number of moles of solute = 5.131/156.636 = 0.03276 mol