"Published in Newark, California, USA"
The vapor pressure of water at 25°C is 23.756 torr. A solution consisting of 18.913 grams of a non-volatile substance in 36 grams of water has a vapor pressure of 20.234 torr. What is the molecular weight of the solute?
Solution:
From the description of the given problem above, it is an application of Raoult's Law because it involves the vapor pressures of a solute and a solvent. From this method, we can calculate the amount of a non-volatile solute as well as its molecular weight.
The formula or working equation for Raoult's Law is
where
Psolution = is the vapor pressure of a solution
Xsolvent = is the mole fraction of a solvent
P°solvent = is the vapor pressure of pure solvent
Hence, the mole fraction of a solvent which is water is
Therefore, the molecular weight of a solute is
