# Colligative Properties

## One property is Vapor-Pressure Lowering

Vapor-pressure lowering is when the vapor pressure of a pure solvent is greater than the vapor pressure of a solution containing a non-volatile liquid.

## Information

Equation: Psolution= (χsolvent) (P°solvent)

Raoult's Law: this law states that the solvent over the solution is proportional to the fraction of solvent molecules in the solution, only when two-thirds of the molecules are solvent molecules

Facts:

• Colligative properties depend on how many solute particles are present in the solvent and do not depend on the type of solute particles.
• Colligative properties are intensive properties

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## Another property is Freezing-Point Depression

Freezing-point depression is described as the process in which adding a solute to a solvent decreases the freezing point of the solvent.

## Information

Equation: ΔT = i Kf m

Molality: the concentration of a solution expressed in moles of solute per kilogram of solvent

Facts:

• Kf is the freezing-point depression constant
• The freezing point of pure water is 0°C , but just by adding a solvent like salt, the freezing point will lower.

## A third property is Boiling-Point Elevation

Boiling-point elevation describes the idea that the boiling point of a liquid will be higher when another compound is added, meaning that a solution has a higher boiling point than a pure solvent.

## Information

Equation: ΔT= Kb m

Van't Hoff Factor: the ratio between the actual concentration of particles produced when the substance is dissolved, and the concentration of a substance as calculated from its mass

Facts:

• Kb is the boiling-point elevation constant
• The amount of boiling point elevation can be calculated using the Clausius-Clapeyron equation and Raoult's Law.

## The last property is Osmotic Pressure

Osmotic pressure is the pressure that has to be applied to a pure solvent to prevent it from passing into a given solution by osmosis.

## Information

Equation: Π = iMRT

Osmosis: a passage of a solvent from a lower-concentration solution to a higher-concentration solution, through a semi-permeable membrane, separating the two solutions

Facts:

• Osmotic pressure is necessary in plant cells to keep their support.
• Osmotic pressure obeys the same relationship of the same form as the ideal gas law