Colligative Properties of Solutions

By: Ben Griesmer 1°

Colligative Properties

Colligative properties of solutions are properties that depend upon the concentration of solute molecules or ions, but not upon the identity of the solute. Colligative properties include freezing point depression, boiling point elevation, vapor pressure lowering, and osmotic pressure.

Vapor Pressure Lowering (VPL)

Vapor pressure lowering is a colligative property of solutions. This property states that the vapor pressure of a pure solvent is greater than the vapor pressure of a solution containing a non volatile liquid. This lowered vapor pressure leads to boiling point elevation.
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VPL Equations

Change in Vapor Pressure of the Solvent: △P(Solv)=X(Solute) P°(Solv)

Change in vapor pressure of the Solution: P(Solv)=P°(Solv)-△P(Solv)

Mole Fraction of the Solvent: P(Solv) = X(Solv) P°(Solv)

VPL Vocabulary

1.Vapor Pressure: The pressure that a vapor exerts or its partial pressure if mixed with other gasses.

2. Colligative Property: A property of solutions that is directed by the ratio of solute to solvent regardless of the identity of the solute

3.Raoult's Law: States that the vapor pressure of an ideal solution is directly dependent on the vapor pressure of each chemical component and the mole fraction of the component present in the solution.

Facts about VPL

1. If You add Sugar to water its Vapor Pressure is lowered.

2. Although many Chefs add salt to water to make it boil faster, it actually does the opposite and makes it take longer to boil.

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Freezing Point Depression (FPD)

Freezing-point depression is one of the colligative properties, it describes the process in which adding a solute to a solvent decreases the freezing point of the solvent. Some examples of this include salt in water, alcohol in water, or the mixing of two solids which may include impurities, in a finely powdered drug.
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FPD Equations

Calculate The Freezing Point Depression: △T = -Kfm

The Freezing Point of the Solvent In A Solution

Containing a nonvolatile nonelectrolyte: T(Solution) = T(Pure Solvent) +△T

Change in Freezing point relative to pure solvent: ΔTf=Kfm

FPD Vocabulary

1. Freezing Point Depression: Adding A Solute to a Solvent decreases the temperature at which the liquid solvent becomes a solid

2.Vapor Pressure: The vapor that which a pressure exerts, or the partial pressure if mixed with other gasses

3. van t'Hoff factor: A measure of the effect of a solute on colligative properties

4.Freezing point: The point at which a liquid freezes, and the solid and liquid phases are in equilibrium

FPD Facts

1. When a substance freezes, the solid and liquid forms are in equilibrium with each-other

2. When a substance starts to freeze the molecules slow down to to the decrease in temperature.

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Boiling Point Elevation (BPE)

Boiling point elevation describes the phenomenon 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. This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such as water.
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BPE Equations

change in boiling point of the solvent above a solution from that of the pure solvent is directly proportional to the molal concentration of the solute: △T = Kbm

BPE Vocabulary

1. Boiling Point: The temperature at which a liquid boils, with the vapor pressure equal to the given external pressure

2. Boilng Point Elevation: The temperature at which a substance's vapor equals the external pressure when another compound is added.

3. Water Vapor: Liquid H2O in a gaseous form, often caused by hot temperatures.

BPE Facts

1. Boiling Point Elevation is most commonly associated with the boiling of water for cooking by chefs or others. Salt or sugar is commonly added to make the water boil more quickly. However, salt will actually make water take longer to boil, rather than shorten it.

2. Boiling Point elevation will cause water to boil. Boiled water can turn into water vapor which is the reasons we have clouds and rain.

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Osmotic Pressure (OP)

Osmotic pressure is the minimum pressure which needs to be applied to a solution in order to prevent the inward flow of water across a semipermeable membrane. It may also be described as the measure of the tendency of a solution to take in water by osmosis.
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OP Equations

Calculate the Osmotic Pressure: π = MRT

OP Vocabulary

1. Osmotic Pressure: The Hydrostatic pressure exerted by a solution across a semipermeable membrane from a pure solvent

2. Osmosis: The net movement of solvent molecules from a region of high solvent potential to a region of lower solvent potential through a partially permeable membrane

3. Ideal Solution: A solution with thermodynamic properties analogous to those of a mixture of an ideal gas

4. Semi-Permeable Membrane: A membrane that will allow only certain molecules or ions to pass through it by diffusion

OP Facts

1. Since Osmotic Pressure is the factor that causes objects to be passed through or stopped by a Semi-Permeable membrane, it is the reason that life can exist.

2. Osmotic Pressure is most commonly associated with water, however it can be used to explain a large varieties of phenomenons. Osmotic pressure is a huge factor in human and other animals blood in making sure it has the correct volume of salt and water.

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