Question

1. if a small amount of the unknown fails to dissolve in the water, will the molecular weight that you calculate be too high or too low? (1pts)

Explanation:

Step1: Recall colligative - property concept

Colligative properties (such as freezing - point depression, boiling - point elevation) are used to calculate molecular weight. If a substance does not fully dissolve, the actual number of moles of solute in solution is less than assumed.

Step2: Analyze molecular - weight calculation

The formulas for colligative properties assume complete dissociation or dissolution of the solute. When a small amount of the unknown fails to dissolve, the measured colligative - property change is smaller than it should be for the actual amount of the substance present. Since molecular weight is inversely proportional to the colligative - property change in the calculation ($M=\frac{w\times1000}{\Delta T\times K\times m}$, where $M$ is molecular weight, $w$ is mass of solute, $\Delta T$ is colligative - property change, $K$ is the colligative - property constant, and $m$ is mass of solvent), a smaller $\Delta T$ will result in a calculated molecular weight that is too high.

Answer:

The calculated molecular weight will be too high.