Chapter 2: Solutions

2.1 Introduction

Summary: • A solution is a homogeneous mixture of two or more pure substances. • It consists of a solvent and one or more solutes. • The particles of a true solution are very small and uniformly mixed. • Solutions are important in daily life, industries and biological processes.

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2.2 Types of Solutions

Summary: • Solutions can be formed from solids, liquids and gases. • Depending on the physical states of solute and solvent, there are nine types of solutions. • Water is the most commonly used solvent.

Solid in Liquid

Summary: • A solid dissolves in a liquid to form a solution. • Examples: Sugar in water, salt in water.

Solid in Solid

Summary: • A solid dissolves in another solid. • Examples: Brass, bronze and other alloys.

Solid in Gas

Summary: • A solid mixes uniformly with a gas. • Example: Iodine vapour in air.

Liquid in Liquid

Summary: • One liquid dissolves in another liquid. • Examples: Ethanol in water, gasoline.

Liquid in Solid

Summary: • A liquid dissolves in a solid. • Example: Mercury in silver (amalgam).

Liquid in Gas

Summary: • A liquid mixes uniformly with a gas. • Example: Chloroform in nitrogen.

Gas in Liquid

Summary: • A gas dissolves in a liquid. • Examples: Carbon dioxide in soft drinks, oxygen in water.

Gas in Solid

Summary: • A gas dissolves in a solid. • Example: Hydrogen in palladium.

Gas in Gas

Summary: • One gas mixes completely with another gas. • Example: Air.

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2.3 Capacity of Solution to Dissolve Solute

Summary: • Every solvent can dissolve only a limited amount of solute at a given temperature. • As more solute is added, dissolution slows down. • Finally, the solution becomes saturated.

Saturated Solution

Summary: • Contains the maximum amount of solute that can dissolve at a given temperature. • Any extra solute remains undissolved.

Supersaturated Solution

Summary: • Contains more dissolved solute than a saturated solution. • It is unstable and easily forms crystals.

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2.4 Solubility

Summary: • Solubility is the maximum amount of solute that dissolves in a given amount of solvent at a specific temperature. • It is usually expressed as concentration (mol L⁻¹).

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2.4.1 Factors Affecting Solubility

Summary: • Solubility depends on: • Nature of solute and solvent • Temperature • Pressure

(i) Nature of Solute and Solvent

Summary: • "Like dissolves like." • Polar substances dissolve in polar solvents. • Non-polar substances dissolve in non-polar solvents. • Strong intermolecular attraction increases solubility.

(ii) Effect of Temperature on Solubility

Summary: • Most solids become more soluble as temperature increases. • Some solids become less soluble with increase in temperature. • The effect depends on whether dissolution is endothermic or exothermic.

(iii) Effect of Pressure on Solubility

Summary: • Pressure has very little effect on solids and liquids. • Pressure greatly affects the solubility of gases in liquids. • Higher pressure increases the solubility of gases.

Henry's Law

Summary: • The solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid. • Higher gas pressure means greater gas solubility.

Exceptions to Henry's Law

Summary: • Some gases such as ammonia (NH₃) and carbon dioxide (CO₂) do not obey Henry's law. • They react with water, making their solubility higher than expected.

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This completes Part 1 (up to Section 2.4.1).

In Part 2, I'll continue from 2.5 Vapour Pressure of Solutions of Liquids in Liquids up to 2.7 Vapour Pressure Lowering, keeping the same clean Blogger-friendly format.