"Published in Newark, California, USA"
The freezing point constant of toluene is 3.33°C per mole per 1000 g. Calculate the freezing point of a solution prepared by dissolving 0.4 mole of solute in 500 g of toluene. The freezing point of toluene is -95.0°C.
Solution:
The freezing point constant is defined as the number of degrees the freezing point will be lowered per mole of solute per 1000 g or 1 kg of solvent present. This can be written as
where m is the molality of a solution.
From the given problem, the molality of a solute dissolved in toluene is
The freezing point depression is defined as the product of the freezing point constant of a solvent and the molality of a solution.
Hence, the freezing point depression of a solution is
Therefore, the freezing point of a solution is
Note: The good application of freezing point depression is that the ice will keep longer in the container at the lower temperature. Few amount of table salt is added to the crushed ice so that the temperature will be lower than the freezing point of ice which is 0°C. If the temperature is lower than the freezing point, then the ice will not melt in the closed container. The ice cream vendors, food track vendors, and street food vendors are using ice with table salt so that their foods and drinks will keep colder in their container. If you will plan for a picnic and camping, then you can use also ice with table salt especially at the warmer or hotter areas. If the container is left open, then the ice with table salt will melt quite or slowly. Please take note that the ice with table salt will melt for a few days even though the container is closed. Table salt inhibits the melting of ice.