Camphor, C16H16O which has a freezing point of 174°C, has a freezing point depression constant of 40.0°C/m. Explain the usefulness and the limitation of camphor as a solvent for determination of molecular weights. For whose kind(s) of solute would camphor be especially useful?
Look at your last post with the three groups I posted, then determine conditions under which a large Kf is useful.
Camphor is commonly used as a solvent in determining the molecular weight of solutes. The usefulness of camphor as a solvent lies in its ability to cause freezing point depression, which is a colligative property. The freezing point depression constant of camphor determines the extent to which the freezing point of the solution decreases with the addition of a solute.
The freezing point depression constant of camphor is given as 40.0°C/m. This means that for every 1 molal (1 mol solute dissolved in 1 kg of camphor) solution, the freezing point will decrease by 40.0°C. This characteristic is useful because it allows for the determination of the molecular weight of a solute.
When a solute is added to camphor, it disrupts the crystal lattice structure of the pure camphor, lowering its freezing point. By measuring the amount of depression in the freezing point and knowing the freezing point depression constant, one can calculate the molality of the solute in the solution. Subsequently, the molecular weight of the solute can be determined using the formula:
Molecular weight = (Freezing point depression constant × Solvent mass in kg) / Freezing point depression in °C
Now, let's discuss the limitations of camphor as a solvent for determining molecular weights. Firstly, camphor has a relatively high freezing point of 174°C. This limitation restricts its use to solutes that have significantly higher freezing points than camphor itself. If the solute has a freezing point close to or below that of camphor, it becomes challenging to accurately measure the freezing point depression.
Secondly, camphor has a relatively low boiling point, making it volatile at typical laboratory temperatures. This volatility can lead to evaporation during the experiment, which may affect the accuracy of the measurements.
Despite these limitations, camphor is especially useful for solutes with high freezing points. It can be effectively used to determine the molecular weights of compounds such as organic substances, polymers, and certain inorganic substances that have freezing points significantly higher than 174°C.
In summary, camphor is a useful solvent for determination of molecular weights due to its freezing point depression property. However, it has limitations regarding the range of solutes that can be accurately measured and its volatility at laboratory temperatures. Camphor is particularly suitable for solutes that have freezing points significantly higher than its own freezing point of 174°C.