Problem 61 - Chemistry: The Central Science

Question

You make a solution of a nonvolatile solute with a liquid solvent. Indicate whether each of the following statements is true or false. (a) The freezing point of the solution is higher than that of the pure solvent. (b) The freezing point of the solution is lower than that of the pure solvent. (c) The boiling point of the solution is higher than that of the pure solvent. (d) The boiling point of the solution is lower than that of the pure solvent.

Step-by-Step Solution

Answer

(a) False; (b) True; (c) True; (d) False. According to the concepts of freezing point depression and boiling point elevation, the freezing point of a solution is lower, and the boiling point is higher than that of the pure solvent when a non-volatile solute is added to the solvent.

Step 1: (a) The freezing point of the solution is higher than that of the pure solvent.

According to the concept of freezing point depression, the freezing point of a solution is always lower than that of the pure solvent. When a non-volatile solute is added to the solvent, it disrupts its crystalline structure, making it harder for the solvent to transition from liquid to solid. Therefore, this statement is False.

Step 2: (b) The freezing point of the solution is lower than that of the pure solvent.

This statement is the opposite of the previous one. As explained above, the freezing point depression concept states that the freezing point of a solution is indeed lower than that of the pure solvent. As a result, this statement is True.

Step 3: (c) The boiling point of the solution is higher than that of the pure solvent.

According to the concept of boiling point elevation, the presence of non-volatile solute particles in a solvent causes an increase in the boiling point of the solution. The solute particles disrupt the vapor pressure equilibrium between the liquid and vapor phases, making it harder for the solvent molecules to escape from the liquid phase. Thus, more heat (higher temperature) is required for the solution to boil compared to the pure solvent. This statement is True.

Step 4: (d) The boiling point of the solution is lower than that of the pure solvent.

This statement is the opposite of the previous one. As explained above, the boiling point elevation concept states that the boiling point of a solution is higher, not lower, than that of the pure solvent. Therefore, this statement is False.