Colligative Properties

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What are colligative properties?

Colligative properties are properties of solutions that depend on the number of solute particles rather than the type or nature of the solute.

Name four main colligative properties.

The four main colligative properties are vapor pressure lowering, freezing point depression, boiling point elevation, and osmotic pressure.

How does vapor pressure lowering occur?

Vapor pressure lowering occurs because the solute particles occupy space at the liquid surface, reducing the number of solvent molecules that can escape into the vapor phase.

What is the formula for vapor pressure lowering?

The formula for vapor pressure lowering is ΔP = X_solute * P^0_solvent, where X_solute is the mole fraction of the solute and P^0_solvent is the vapor pressure of the pure solvent.

Define freezing point depression.

Freezing point depression is the phenomenon where the freezing point of a solution is lower than that of a pure solvent, due to the presence of solute particles.

What is the equation for freezing point depression?

The equation for freezing point depression is ΔT_f = i * K_f * m, where ΔT_f is the freezing point depression, i is the van’t Hoff factor, K_f is the freezing point depression constant, and m is the molality of the solution.

Describe boiling point elevation and its cause.

Boiling point elevation occurs when a solution's boiling point is higher than the pure solvent's due to solute particles, which require a higher temperature to reach the vapor phase equilibrium.

What is the formula for calculating boiling point elevation?

The formula for boiling point elevation is ΔT_b = i * K_b * m, where ΔT_b is the boiling point elevation, i is the van’t Hoff factor, K_b is the ebullioscopic constant, and m is the molality of the solution.

Explain osmotic pressure in the context of colligative properties.

Osmotic pressure is the pressure required to stop the flow of solvent into a solution through a semipermeable membrane, driven by solute concentration.

What equation is used to determine osmotic pressure?

The equation for osmotic pressure is 𝜋 = i * M * R * T, where 𝜋 is the osmotic pressure, i is the van’t Hoff factor, M is the molarity, R is the ideal gas constant, and T is the temperature in Kelvin.

Why do colligative properties not depend on the identity of a solute?

Colligative properties depend only on the number of solute particles in a solution, not on their chemical identity, because the impact they have is purely physical (based on concentration).

In what way does vapor pressure lowering affect boiling point?

Vapor pressure lowering raises the boiling point since a higher temperature is needed for the solution’s vapor pressure to match atmospheric pressure.

How do non-volatile solutes affect colligative properties?

Non-volatile solutes affect colligative properties by reducing vapor pressure, causing boiling point elevation, freezing point depression, and increasing osmotic pressure.

Can colligative properties be used to determine molar mass?

Yes, colligative properties can be used to determine molar mass by measuring changes in boiling/freezing points or osmotic pressure and using related equations to calculate molar mass.

What is the van’t Hoff factor and its significance in colligative properties?

The van’t Hoff factor (i) represents the number of particles a solute forms in solution, directly affecting the extent of colligative properties.


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