Question

Which colligative property does not involve a phase change? Give an example of its importance.

Short answer

Osmotic pressure; it's important for cell water balance in biological systems.

Step-by-step solution

Understanding Colligative Properties

Colligative properties are properties of solutions that depend on the number of solute particles, not the identity of the solute. They include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure.

Identify Colligative Properties Involving Phase Changes

Out of the four colligative properties, boiling point elevation and freezing point depression involve a phase change. Boiling point elevation affects the transition from liquid to gas, and freezing point depression affects the transition from liquid to solid.

Identify Colligative Properties Not Involving Phase Changes

Vapor pressure lowering and osmotic pressure do not directly involve a phase change. Vapor pressure lowering affects the tendency of particles to escape into the vapor phase, while osmotic pressure relates to the movement of solvent through a semipermeable membrane.

Choose the Correct Colligative Property

Osmotic pressure is the colligative property that does not involve a phase change, as it concerns the movement of solvent molecules across a semipermeable membrane without a change in phase.

Provide an Example of Its Importance

Osmotic pressure is important in biological systems, particularly in the maintenance of cell turgor pressure in plants. It allows cells to regulate water balance and maintain their shape by controlling the movement of water across the cell membrane.

Key concepts

Osmotic Pressure

Osmotic pressure is a fascinating colligative property that does not involve a phase change. It occurs when a solvent, like water, moves across a semipermeable membrane from an area of low solute concentration to an area of high solute concentration.
This movement continues until the concentration is equal on both sides or the pressure equals the osmotic pressure.

• The process helps plants maintain turgor pressure, which is vital for keeping them upright and enabling the leaves to catch sunlight effectively.
• It's crucial in kidneys for regulating water balance and salt concentration in the body.

If osmotic pressure is not maintained, cells can either shrink or swell, causing dysfunction. This is why osmotic pressure is essential for the survival of living organisms.

Phase Change

Phase changes occur when a substance transitions from one state of matter to another. For example, from solid to liquid (melting) or liquid to gas (vaporization).

• In colligative properties, boiling point elevation deals with the transition from liquid to gas.
• Freezing point depression addresses the transition from liquid to solid.

Substances require additional energy to change phase due to intermolecular forces. When a solute is added to a solvent, it affects these transitions by altering the freezing and boiling points. This is largely because the solute particles interfere with the formation of the solid structure or influence vapor escape.
Both boiling point elevation and freezing point depression are instrumental in everyday phenomena like cooking and antifreeze's function in vehicles.

Vapor Pressure Lowering

Vapor pressure lowering is another colligative property that does not involve a direct phase change. This concept refers to the decrease in pressure exerted by the vapor in equilibrium with its liquid.

• Adding a non-volatile solute to a solvent reduces the solvent's tendency to escape into the gas phase.
• This makes the solution’s vapor pressure lower than that of the pure solvent.

This lowering is because the solute particles take up space at the liquid's surface, leaving fewer solvent molecules to evaporate. This aspect is essential in understanding processes like the preservation of liquids or the behavior of solutions in various environments.
Moreover, vapor pressure lowering explains why saltwater doesn’t evaporate as quickly as pure water, which is fundamental in many natural and industrial processes.