Solubility for board exam class 12 as well as for JEE mains and Advance, NEET

Introduction

 Solubility is the ability of a solute (substance being dissolved) to dissolve in a solvent (the medium in which it dissolves) to form a homogeneous solution at a given temperature and pressure.

• Solute: substance that dissolves

• Solvent: substance that dissolves the solute

• Solution: homogeneous mixture formed

Definition

Solubility is usually expressed as the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature and pressure.

Types of Solubility

Solubility is classified according to the physical state of solute and solvent.

1. Solid in Solid

2. Solid in Liquid

3. Liquid in Liquid

4. Gas in Liquid

1. Solubility of Solid in Solid

In this case, both solute and solvent are solids. When they mix uniformly, they form a solid solution.

Two types of solid soution found

1. Substitutional solid solution

2. Interstitial solid solution

Substitutional solid solution

Example

• Alloys

• Brass = Zinc dissolved in Copper

• Bronze = Tin dissolved in Copper

Figure (Solid in Solid)

Pure Copper atoms: Copper + Zinc atoms (Brass alloy)

● ● ● ● ●                      ● ● ● ○ ●
● ● ● ● ●      →            ● ○ ● ● ●
● ● ● ● ●                      ● ● ○ ● ●

● = Copper atoms
○ = Zinc atoms

Explanation

• Zinc atoms replace some copper atoms in the crystal lattice.

• The mixture becomes uniform at atomic level.

2. Interstitial Solid Solution

• Small atoms occupy spaces (interstices) between solvent atoms.

Example:

• Steel, where Carbon atoms fit between Iron atoms.

Solvent lattice (A atoms)

A       A

    A

A       A

Small solute atoms (B) in gaps

A   B   A

  A   B

A   B   A

2. Solubility of Solid in Liquid

This is the most common type of solubility where a solid dissolves in a liquid.

Examples

• Salt in water

• Sugar in water

• Potassium nitrate in water

Figure (Solid in Liquid)

Before Dissolving

Water molecules:     Salt crystal:

○ ○ ○ ○ ○            ■ ■ ■
○ ○ ○ ○ ○            ■ ■ ■
○ ○ ○ ○ ○            ■ ■ ■


After Dissolving

○ ○ ■ ○ ○
■ ○ ○ ○ ■
○ ■ ○ ○ ○
○ ○ ○ ■ ○

○ = Water molecules
■ = Dissolved salt ions
Explanation
Solid particles break into ions or molecules.
They get surrounded by solvent molecules.
Example reaction:
NaCl(s) → Na⁺(aq) + Cl⁻(aq)
Factors affecting solubility
Temperature
Generally increases solubility of solids.
Nature of solute and solvent
"Like dissolves like"
Pressure
Little effect on solids.
3. Solubility of Liquid in Liquid
This occurs when one liquid dissolves in another liquid.
Types
(a) Completely miscible liquids
Liquids mix in all proportions.
Examples:
Alcohol + water
Acetone + water
4. Solubility of Gas in Liquid
Solubility of a gas in a liquid is the maximum amount of gas that can dissolve in a given amount of liquid at a specific temperature and pressure to form a homogeneous solution.
Example: Carbon dioxide dissolving in water to make soda drinks.
Factors affecting
1. Nature of Gas and Liquid
Solubility depends on the interaction between gas molecules and liquid molecules.
Polar gases dissolve better in polar liquids.
Non-polar gases dissolve better in non-polar liquids.
Example:

Ammonia is highly soluble in water because it forms hydrogen bonds with Water.
2. Effect of Temperature
The solubility of most gases decreases with increase in temperature.
Reason:
Dissolution of gas is generally exothermic.
Increasing temperature provides energy for gas molecules to escape from the liquid.
Example:
Cold water contains more dissolved Oxygen than warm water.
This is important for aquatic life such as Fish.
4. Effect of Nature of Solvent
The solvent must have good intermolecular attraction with gas molecules.
Examples:
Ammonia is very soluble in Water.
Oxygen is only slightly soluble in water.
Thank you !!!
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