Define the term colligative property. Suppose the freezing point of a solution o

Question

Define the term colligative property. Suppose the freezing point of a solution of 2.00 g of an unknown molecular substance is 10.00 g of the solvent benzene is measured. If the solution freezes at a temperature of 6.33 degree C lower than pure benzene itself, calculate the molar mass of the unknown substance. For a given number of modes of solute, why do ionic substances have a larger effect on the freezing and boiling points of solvents than do nonionic substances? To study the phenomenon of freezing point depression, a Colligative Property. To determine the molar mass of an unknown solute. When a solute is dissolved in a solvent, the properties of the solvent are changed by the presence of the solute. The magnitude of the change generally is proportional to the amount of solute added. Some properties of the solvent are changed only by the number of solute particles present, without regard to the particular nature of the solute. Such properties are called colligative properties of the solution. Colligative properties include changes in vapor pressure, boiling point, freezing point, and osmotic pressure. For example, if a nonvolatile, nonionizing solute is added to a volume solvent (such as water), the amount of solvent that can escape from the surface of the liquid at a given temperature is lowered, relative to the case where only the pure solvent is present. The vapor pressure above a such a solution will be lower than the vapor pressure above a sample of the pure solvent, thereby preventing as many molecules from evaporating at a given temperature. (See Figure 1.) As shown in the figure, if the vapor pressure of the solution is lowered, there is an increase in the melting point of the solution as well as a decrease in the freezing point. In this experiment, you will determine the freezing point of a pure solvent (c-hexane) and a solution dissolvent in c-hexane. The pressure of a nonvolatile solute lowers the vapor pressure of this solvent by blocking the surface.

Explanation / Answer

1. Colligative properties of solutions are properties that depend upon the concentration of solute molecules or ions, but not upon the identity of the solute.

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