Short Answer

Solubility is affected by several factors, including the nature of the solute and solvent, temperature, pressure, and particle size. Some substances dissolve easily because their particles attract the particles of the solvent strongly. Others dissolve slowly or not at all if this attraction is weak.

Temperature mostly increases solubility of solids in liquids, while pressure mainly affects gases. Stirring and smaller particle size also increase the rate of dissolving. These factors together decide how much of a substance can dissolve in a given amount of solvent.

Detailed Explanation

Factors affecting solubility

Solubility refers to the amount of a substance (solute) that can dissolve in a given amount of solvent under specific conditions. Different substances dissolve in different amounts because their particles interact in various ways with solvent particles. Solubility is an important concept in chemistry because it helps explain many natural and industrial processes, such as dissolving sugar in water, preparing medicines, mixing chemicals, and purifying substances.

Several factors influence how much solute can dissolve and how fast it dissolves. These factors include the nature of the solute and solvent, temperature, pressure, particle size, and stirring. Each factor plays a specific role in determining the solubility of solids, liquids, and gases.

1. Nature of solute and solvent

The most important factor affecting solubility is the chemical nature of the solute and solvent. Some solutes dissolve easily in certain solvents because their particles attract each other strongly.

A key rule is:
“Like dissolves like.”

Examples:

• Polar solutes dissolve well in polar solvents (e.g., salt in water).
• Non-polar solutes dissolve well in non-polar solvents (e.g., oil in petrol).

If the attraction between solute and solvent particles is strong, solubility increases. If weak, solubility decreases.

2. Temperature

Temperature has a major effect on solubility, especially for solids and gases.

Effect on solids in liquids

• Increasing temperature generally increases solubility.
• Heat gives more energy to solute particles, helping them break apart and mix with solvent.

Example: More sugar dissolves in hot water than in cold water.

Effect on gases in liquids

• Increasing temperature decreases solubility of gases.
• Gas particles escape out of the liquid faster when heated.

Example: Cold water holds more dissolved oxygen than warm water.

3. Pressure

Pressure mainly affects the solubility of gases in liquids.

• High pressure increases gas solubility.
• Low pressure decreases gas solubility.

This is because pressure forces gas particles into the liquid, allowing more of them to dissolve.

Examples:

• Carbonated drinks are bottled under high pressure to dissolve more CO₂.
• When a bottle is opened, pressure drops and CO₂ escapes as bubbles.

Pressure has little effect on solids or liquids.

4. Particle size of solute

Particle size affects how fast solubility occurs, not how much will finally dissolve.

• Smaller particles dissolve faster because they have a larger surface area.
• Larger particles dissolve slowly.

Examples:

• Powdered sugar dissolves faster than sugar cubes.
• Fine salt dissolves quicker than coarse salt.

Although particle size speeds up dissolving, the final solubility remains the same.

5. Stirring or agitation

Stirring increases the rate of dissolving by bringing fresh solvent particles into contact with the solute.

• Stirring speeds up the dissolving process.
• Without stirring, solubility is slower, especially for solids.

Examples:

• Stirring tea helps sugar dissolve quickly.
• Medicines dissolve faster when stirred in water.

Stirring does not change the maximum solubility but only the speed.

6. Presence of other substances

Other substances in the solvent can:

• increase solubility
• decrease solubility
• compete with solutes

Examples:

• Salt in water decreases the solubility of oxygen.
• Mixed solvents (like alcohol + water) dissolve some substances better.

7. Pressure and temperature together for gases

Gases follow Henry’s Law, which states that:

• Solubility increases with pressure.
• Solubility decreases with temperature.

This explains why aquatic life suffers in warm, polluted waters—less oxygen dissolves.

8. Chemical reactions with the solvent

Some solutes dissolve better if they react chemically with the solvent.

Examples:

• Sodium reacts with water to form sodium hydroxide, increasing solubility.
• Carbon dioxide reacts with water to form carbonic acid.

Chemical reactions increase the amount that dissolves.

9. Polarity and intermolecular forces

Solubility depends on:

• hydrogen bonding
• dipole–dipole attraction
• Van der Waals forces

Water dissolves many ionic and polar solutes because it is a highly polar solvent.

Non-polar solvents dissolve oils, waxes, and fats because of similar forces.

Conclusion

Solubility is influenced by several important factors such as the nature of the solute and solvent, temperature, pressure, particle size, and stirring. Solids dissolve better at higher temperatures, while gases dissolve better at high pressure and low temperature. The chemical properties of substances and their interactions also play a major role in determining solubility. Understanding these factors helps us explain many everyday situations, from dissolving sugar in tea to preparing medicines and soft drinks.