Chapter 2 – Mixtures & Separation

🔬 What is a Mixture?

A mixture consists of two or more substances that are physically combined (not chemically). The components can be separated by physical methods.

Mixture	Components
🌊 Sea water	Water + salt + other dissolved substances
🌬️ Air	Nitrogen + oxygen + CO₂ + inert gases
🟦 Copper (II) sulfate solution	Copper (II) sulfate + water
🟤 Salt + ammonium chloride	Sodium chloride + ammonium chloride

📌 Key Point

In a mixture, the substances are NOT chemically joined. They keep their original properties and can be separated using physical methods.

⚗️ Three Separation Techniques

🌡️

Sublimation

Used when ONE solid in a mixture turns directly from solid → gas on heating (without melting first).

💎

Crystallisation

Used to get solid crystals from a solution. The solution is heated until saturated, then cooled.

🌊

Simple Distillation

Used to separate a solvent (like water) from a solution. Involves boiling and condensing.

🌡️ Sublimation – In Detail

Sublimation = a solid changes directly into a gas (without becoming a liquid first).

Examples of solids that sublime: Ammonium chloride (NH₄Cl) and Iodine (I₂)

🔬 Experiment: Separating ammonium chloride from sodium chloride

1

Place the mixture in an evaporating dish

2

Place an inverted glass funnel over the dish

3

Plug the narrow end of the funnel with cotton wool (stops vapour escaping)

4

Heat the dish with a Bunsen burner

5

Ammonium chloride turns to vapour → travels up → cools → forms white solid on funnel walls (sublimate)

6

Sodium chloride stays in the dish (does not sublime)

💡 Key Vocabulary

Sublimate = the solid that forms on the inner surface of the funnel after the vapour cools.
Residue = the solid left behind in the evaporating dish.

💎 Crystallisation – In Detail

Crystallisation = obtaining crystals of a dissolved solid (solute) from its solution.

Used when: You want to get crystals of a soluble salt (e.g. copper sulfate crystals from copper sulfate solution). Not suitable if the solid decomposes on strong heating (e.g. sugar).

🔬 Steps in crystallisation:

1

Pour the solution (e.g. copper sulfate) into an evaporating dish

2

Heat gently on a water bath until most water evaporates

3

Test with a glass rod — if small crystals appear, the solution is saturated

4

Stop heating and allow to cool — crystals form!

5

Remove crystals with a spatula, wash with water, dry between filter papers or in sunlight

📌 Key Terms

Saturated solution = no more solute can dissolve at that temperature.
Solubility = the amount of a substance that dissolves in a solvent at a given temperature.

🌊 Simple Distillation – In Detail

Simple distillation = separating the solvent from a solution.

Example: Getting pure water from copper sulfate solution.

🔬 How it works:

1

Heat the solution in a distillation flask — water boils and turns to vapour

2

Vapour travels through the condenser where it cools and becomes liquid

3

Pure liquid (the distillate) collects in the conical flask (receiver)

4

Copper sulfate stays in the distillation flask

Precaution	Reason
Add boiling chips (anti-bumping granules)	To ensure smooth boiling
Thermometer bulb at side-arm of flask	To measure boiling point of solvent
Condenser slopes downward	Distillate flows easily into receiver
Cold water enters bottom of condenser	Ensures efficient cooling of vapour

💡 Key Word

Distillate = the pure liquid collected in the receiver after condensation.

📊 Summary Comparison Table

Technique	Used For	Example
🌡️ Sublimation	Separating two solids (one sublimes)	NH₄Cl from NaCl
💎 Crystallisation	Getting crystals of solute from solution	Copper (II) sulfate crystals from solution
🌊 Simple Distillation	Separating solvent from solution	Pure water from copper sulfate solution

🧪 Unit C2: Mixtures & Separation