# Solution and Colligative Properties Formulas for NEET

A solution is a homogeneous mixture of two or more substances on a molecular level. The constituent of the mixture present in a smaller amount is called the solute and the one present in a larger amount is called the solvent.

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## Osmotic Pressure

Osmotic Pressure is the best colligative property to determine the molecular weight of non-volatile substances.

## Types of Solutions

Fluids in the body generally aren’t found in pure forms. They are usually found in three types of solutions: isotonic, hypotonic and hypertonic.

• Isotonic solutions – An isotonic solution has the same solute concentration as another solution.
• Hypotonic solution – A hypotonic solution has a lower solute concentration than another solution.
• Hypertonic solution – A hypertonic solution has a higher solute concentration than another solution.

## Van’t Hoff Correction Factor

To explain the abnormal values of colligative properties and consequently molecular masses a correction factor known as Van’t Hoff Factor is employed.

## Relative Lowering of Vapour Pressure

It is the ratio of lowering of vapour pressure to vapour pressure of pure solvent.

Relative lowering of vapour pressure is

## Raoult’s Law

The partial pressure of a solvent is equal to the product of mole fraction of the solvent and its vapour pressure in a pure state.

## Determination of Molecular Mass of a Solute

Measurement of boiling point elevation or freezing point depression using Beckmann thermometer is a convenient method for the determination of the molecular masses of the solutes. In fact, it is a method of determining the number of moles of the solute particles present in a solution.

Mass of solute present in 1kg solvent.

Using the relation

Similarly, depression in freezing point is measured

## Ideal Solutions

The solutions are said to be ideal if they fulfil the following requirements.

They obey Raoult’s law

ΔHmix = 0

ΔVmix = 0

In case of ideal solutions, the vapour pressure of the solution is a linear function of mole fraction.

## Non-ideal Solution with Positive Deviations

Non-ideal solutions exhibit positive deviations from Raoult’s law.

In such solutions.

ΔHmix > 0

ΔVmix > 0

The vapour pressure of the solution, in this case, is always larger than that expected from ideal behaviour.

## Non-ideal Solution with Negative Deviations

Non-ideal solutions exhibit negative deviations from Raoult’s law.

In such solutions.

ΔHmix < 0

ΔVmix < 0

The vapour pressure of the solution, in this case, is always smaller than that expected from ideal behaviour.

## Henry Law

Henry law deals with the variation of solubility of gases in liquids with pressure. It states that solubility of gas at a given temperature is directly proportional to the pressure at which it is dissolved.

This expression is identical with Raoult’s law for a volatile solute. All systems which obey Raoult’s law must satisfy Henry’s law, but the reverse will only be true if Henry’s law applies over the whole range of concentration.

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