Utterly Confused About Colligative Properties

Let s examine a few examples of how to approach colligative property problems. We will begin with a Raoult s law example. 

What is the vapor pressure of a solution made by mixing 80.0 g of chloroform, CHCl3, in 800.0 g of carbon tetrachloride, CCl4 The vapor pressure of chloroform is 197 torr, and the vapor pressure of carbon tetrachloride is 114 torr (all vapor pressures are determined at 25°C). 

Raoult s law requires the mole fraction of each volatile material. Whenever the mole fraction is not present, we will need to calculate the value from the number of moles. In this example, we must begin by calculating the moles of each constituent of the solution. 

Moles carbon tetrachloride = (800.0 g CC14) (1 mol CC14/153.823 g CC14) 

It is possible to calculate the mole fraction of carbon tetrachloride (solvent) in a similar manner. However, simply subtracting the mole fraction of chloroform from 1 will give the same value. 

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