Question

How do the freezing point and boiling point of ocean water differ compared to those of distilled water?
A. Ocean water freezes at a lower temperature and boils at a lower temperature.
B. Ocean water freezes at a lower temperature and boils at a higher temperature.
C. Ocean water freezes at a higher temperature and boils at a lower temperature.
D. Ocean water freezes at a higher temperature and boils at a higher temperature.

Answer 1

Hint: Huge amount of salts are dissolved in ocean water when compared to distilled water.
Addition of solute into solvent affects the freezing point and boiling point of the solvent.

Complete step by step answer:
Freezing point is the temperature at which a liquid changes into a solid. If we add solute to a pure solvent the freezing point of the solution will be less than that of the pure solvent. This is known as the lowering of freezing point or freezing point depression.
Boiling point is the temperature at which a liquid changes into a gas. On adding solute into a pure solvent, the boiling point of the solution will become greater than that of the pure solvent. This is known as the elevation of boiling point.
In order to solve this problem, we need to know the colligative properties of solutions. Colligative properties of solutions are the properties that depend on the ratio of number of solute particles to the number of solvent molecules in the solution.
The lowering of freezing point and elevation of boiling point are two colligative properties.
Freezing point is the temperature at which a liquid changes into a solid. If we add solute to a pure solvent the freezing point of the solution will be less than that of the pure solvent. This is known as the lowering of freezing point or freezing point depression.
Boiling point is the temperature at which a liquid changes into a gas. On adding solute into a pure solvent, the boiling point of the solution will become greater than that of the pure solvent. This is known as the elevation of boiling point.
Huge amounts of salts are dissolved in ocean water when compared to distilled water. Due to the presence of these solutes there will be lowering of freezing point or freezing point depression and elevation of boiling point for ocean water.
When solute is present, the surface layer of solution will contain both solute molecules and solvent molecules this reduces the vapor pressure of solvent that is why the boiling point increases. Similarly, the freezing point decreases.
So, the answer is option B. That is, ocean water freezes at a lower temperature and boils at a higher temperature.

Note: Colligative properties depend only on the ratio of number of solute particles to the number of solvent molecules in the solution. It does not depend on the chemical nature of the solute.