Class 12 Chemistry Chapter 2 Notes – Solutions

Classification of solutions

Binary solutions are those that have only two components. Components are the elements that make up a solution. The solvent is the element with the highest concentration. The solvent determines the physical structure of a solution.

The other element in the solutions that are found in lesser levels is referred to as a solute. Every element may exist as a solid, liquid, or gas.

Class 12 Chemistry Chapter 2 Notes - Solutions

Important Definitions

Solution: The term “solution” refers to a fully homogeneous mixture of two or more components.

Solute: A solute is a substance that is existing in a smaller amount or whose physical state changes during the production of a solution.

Solvent: A solvent is a component that is present in greater amounts and affects the physical condition of a solution.

Solubility: Solubility refers to the maximum amount of a chemical that may be dissolved in a given amount of solvent at a certain temperature.

Osmosis: The solvent particles travel from the solvent side to the solution side when a semipermeable membrane divides a pure solvent and a solution. This occurrence is referred known as “osmosis.” Just small molecules pass through the semi-permeable barrier, which blocks larger solute molecules.

Osmotic Pressure: The osmotic pressure of a solution is the extra pressure that must be applied to a solution to prevent osmosis or the passage of solvent molecules into the solution over a semipermeable barrier. The extra pressure must match the osmotic pressure. A coating should be applied to the solution to prevent osmosis.

Isotonic solutions are made up of two liquids with the same osmotic pressure and temperature.

Hypotonic solutions: A solution having a lower concentration or lower osmotic pressure is referred to as “Hypotonic” in comparison to a highly concentrated solution.

Hypertonic solution: A solution having a higher concentration or higher osmotic pressure than a dilute solution is known as “hypertonic.”

Reverse Osmosis: If a pressure higher than the osmotic pressure is exerted on the solution side, the solvent will move from the solution into the pure solvent across the semi-permeable membrane (SPM). Reverse osmosis is the name of the procedure.

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Whenever a pressure greater than the osmotic pressure is given to a liquid, reverse osmosis occurs.

Factors impacting a solid’s solubility in a liquid include:

Nature of solute and solvents: Polar solutes disperse in polar solvents, whereas non-polar solutes dissolve in non-polar solvents.

Temperature impact: If the dissolution process is endothermic (solH > 0), the solubility rises as the temperature rises. If the dissolving is exothermic (solH 0), the solubility falls as the temperature rises.

Pressure impact: The impact of pressure on the solubility of solids in liquids is negligible since solids are highly incompressible.

Factors impacting a gas’s solubility in a liquid include:

Effects of pressure: The relative pressure of the gas in the vapour phase (p) is proportional to the mole fraction of the gas (x) in the solution, according to Henry’s law. p = KH x, where KH is Henry’s law constant, which varies depending on the gas and temperature. The lesser the solubility of the gas in the liquid, the greater the value of KH at a given pressure.

Effects of temperature: Because dissolution is an exothermic process, the solubility should drop as the temperature rises, as per Le Chatelier’s principle.

Ideal and non-ideal solutions:

Azeotropes: Constant boiling mixes, also known as azeotropes, are liquid mixtures that boil at the same degree as a pure liquid and have the same proportion of constituents in the liquid and vapour phases.

Minimum boiling azeotropes: These are created by liquid couples that deviate from ideal behaviour, such as an ethanol-water combination.

Maximum boiling azeotropes: These are created by liquid couples that deviate from ideal behaviour, such as a nitric acid-water mixture.

Colligative properties: Colligative qualities are those that are determined only by the number of solute particles dispersed in a specific amount of solvent rather than the nature of the solute.

Osmosis and osmotic pressure

Osmosis is the process of moving solvent molecules from a less concentrated solution to a more concentrated solution over a semipermeable membrane. Osmotic pressure refers to the hydrostatic pressure that arises as a result of osmosis, or the excess pressure that must be given to the solution to prevent osmosis.

Solutions’ Effectiveness

The amount of salt solvated per unit of solution or solvent is referred to as solution strength. The strength of a solution can be determined in a variety of ways.

1. Mass Percentage (%w/w): “It denotes the mass of a component in 100 g of solution.”

Class 12 Chemistry Chapter 2 Notes - Solutions

2. Volume Percentage (%v/v): “It represents the volume of a component in a solution of 100 mL.”

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3. Parts per million: Whenever a solute is present in trace amounts, the concentration is expressed in parts per million (ppm), which is specified as:

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4. Mole fraction: The common symbol for mole fraction is x, and the component is denoted by the subscript on the right hand side of x. It is defined as follows:

Mole fraction

5. Molarity: The number of moles of solute dissolved in one litre (or one cubic decimetre) of solution is known as molarity (M).


6. Molality: Molality (m) is the number of moles of solute per kilogramme (kg) of solvent and is stated as:

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Henry’s law

In liquids, the dissociation of gas is controlled by Henry’s law. The states that, the solubility of a gas in a liquid, at a given temperature, is directly proportional to the partial pressure of the gas. Due to the presence of a non-volatile solute, the vapour pressure of the solvent is lowered.

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The constant KH stands for Henry’s law.

Raoult’s Law

The lowering of the vapour pressure of the solvent is ruled by Raoult’s law. The law states that the relative lowering of the vapour pressure of the solvent over a solution and the mole fraction of a non-volatile solute present in the solution is equal. It is expressed as:

Ptotal= p10x1+p20x2

Depression of Freezing Point

In comparison to the freezing point of pure solvent, lowering the vapour pressure of a solution lowers the freezing point. We understand that at a substance’s freezing point, the solid phase and liquid phase are in dynamic equilibrium. As a result, a material’s freezing point is known as the temperature where the vapour pressure of the material in its liquid phase equals the vapour pressure of the substance in its solid phase.

Depression of Freezing Point
Tf, or the depression of a solvent’s freezing point in a solution, is depicted in this diagram.

Frequently Asked Questions on CBSE Class 12 Chemistry Chapter 2 Notes: Solutions

1. What are the many kinds of solutions?

2. What are ‘Ideal solutions’?

3. What are Homogeneous Mixtures?

4. Explain the role of molecular interaction in a solution of water and alcohol?

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