colligative properties of solution

Colligative Properties of Solutions

Colligative properties are physical properties of a solution that depend only on the number of solute particles, not on the type of solute.

This means: Different substances can produce the same colligative effect if they have the same number of particles in solution.

Types of Colligative Properties

There are four main colligative properties:

1? Vapor Pressure Lowering

Explanation

When a non-volatile solute is added to a solvent, the vapor pressure of the solution decreases compared to the pure solvent.

Example:

Pure water evaporates faster than sugar solution.

Formula

Where:

P = lowering of vapor pressure

= vapor pressure of the pure solvent

= mole fraction of solute

2? Boiling Point Elevation

Explanation

A solution boils at a higher temperature than the pure solvent.

Example:

Pure water boils at 100C

Salt solution boils above 100C

Formula

Where:

Tb = boiling point elevation

= Vant Hoff factor

= boiling point elevation constant

= molality (mol solute/kg solvent)

3? Freezing Point Depression

Explanation

A solution freezes at a lower temperature than the pure solvent.

Example:

Pure water freezes at 0C

Salt solution freezes below 0C

Formula

Where:

Tf = freezing point depression

= freezing point depression constant

4? Osmotic Pressure

Explanation

Osmotic pressure is the minimum pressure required to stop osmosis through a semipermeable membrane.

Example:

Red blood cells shrink or burst due to osmotic pressure differences.

Formula

Where:

= osmotic pressure

M = molarity

R = gas constant

T = temperature (Kelvin)

Vant Hoff Factor (i)

The Vant Hoff factor represents the number of particles produced when a solute dissolves in a solution.

Substance

i

Glucose (CHO)

1

NaCl

2

CaCl

3

Non-electrolytes i = 1

Strong electrolytes i > 1

Summary

Colligative properties depend on the number of solute particles

They do not depend on the chemical nature of the solute

There are four colligative properties

More particles greater colligative effect

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