Simple and Fractional Distillation

This lesson covers two important distillation techniques — simple distillation and fractional distillation — as required by the Edexcel GCSE Chemistry specification (1CH0, Topic 1). You need to know the apparatus, method, and scientific principles for each, and be able to explain when each technique is appropriate. Distillation also links to the fractional distillation of crude oil, which is an important industrial application.

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Simple Distillation

Simple distillation is used to separate a solvent from a solution. It allows you to collect the liquid (solvent) separately from the dissolved solid or other liquid.

When to Use Simple Distillation

• To obtain pure water from salt water.
• To separate a solvent from a dissolved solid when you want to keep the solvent.
• When there is only one liquid to collect.

How It Works

1. The solution is heated in a round-bottomed flask (or distillation flask) until the solvent boils.
2. The solvent turns into vapour (gas) and rises up through the flask.
3. The vapour passes into a condenser (a glass tube surrounded by a cold-water jacket).
4. In the condenser, the vapour is cooled and turns back into a liquid (condenses).
5. The pure liquid is collected in a collection vessel (beaker or conical flask) at the other end of the condenser.
6. The dissolved solid remains in the flask.

Apparatus

Component	Purpose
Distillation flask	Holds the solution being heated
Thermometer	Measures the temperature of the vapour to confirm the correct boiling point
Condenser (Liebig condenser)	Cools the vapour back into a liquid
Cold water in / out	Cold water flows through the outer jacket of the condenser in the opposite direction to the vapour (counter-current)
Collection vessel	Collects the condensed liquid (distillate)
Heat source	Bunsen burner, electric heater or heating mantle

Key Points

• The thermometer reading confirms the identity of the liquid being collected. For pure water, it should read 100 \u00b0C (at standard atmospheric pressure).
• Cold water enters the condenser at the bottom and exits at the top. This creates a counter-current that maximises cooling efficiency.
• The liquid collected is called the distillate.

Exam Tip: When describing simple distillation, always mention the role of the condenser. It cools the vapour so it condenses back into a liquid. Without the condenser, the vapour would simply escape into the air and you would not collect the solvent.

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Fractional Distillation

Fractional distillation is used to separate a mixture of two or more miscible liquids (liquids that mix together) with different boiling points.

When to Use Fractional Distillation

• To separate ethanol from water.
• To separate the components of crude oil.
• To separate any mixture of miscible liquids.

How It Works

1. The mixture is heated in a flask. The liquid with the lowest boiling point evaporates first.
2. The vapours rise up through a fractionating column — a tall glass column packed with glass beads or containing glass plates.
3. The fractionating column has a temperature gradient: it is hottest at the bottom and coolest at the top.
4. Vapours of liquids with higher boiling points condense on the glass beads in the column and drip back down into the flask. They have not reached a high enough temperature to remain as vapour.
5. Only the vapour of the liquid with the lowest boiling point reaches the top of the column, passes into the condenser, and is collected.
6. Once the first liquid has been collected (the thermometer reads its boiling point), the temperature is increased to collect the next liquid, and so on.

Apparatus

The apparatus is the same as simple distillation, with the addition of:

Component	Purpose
Fractionating column	Provides a temperature gradient; allows vapours with higher boiling points to condense and return to the flask
Glass beads / packing	Increase the surface area for condensation inside the column

Key Differences from Simple Distillation

Feature	Simple Distillation	Fractional Distillation
Used for	Separating a solvent from a solution	Separating miscible liquids
Fractionating column	Not needed	Essential
Number of liquids collected	One	Two or more
Boiling point difference	Large (or only one liquid)	Can separate liquids with similar boiling points

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Choosing a Distillation Method

flowchart TD
    A["What do you want to separate?"] --> B{"Is it a solvent from a dissolved solid?"}
    B -->|Yes| C["Use Simple Distillation"]
    B -->|No| D{"Is it a mixture of miscible liquids?"}
    D -->|Yes| E["Use Fractional Distillation"]
    D -->|No| F["Consider another technique<br/>(filtration, chromatography, etc.)"]

    style A fill:#3498db,color:#fff
    style C fill:#27ae60,color:#fff
    style E fill:#27ae60,color:#fff
    style F fill:#e67e22,color:#fff

Exam Tip: The key difference between simple and fractional distillation is the fractionating column. If a question asks you to describe fractional distillation, you MUST mention the fractionating column and explain how the temperature gradient allows liquids with different boiling points to be separated. Without this, you will not gain full marks.

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Fractional Distillation of Crude Oil

Fractional distillation is used industrially to separate crude oil into useful fractions. This is a major application that links to the organic chemistry topic.

What Is Crude Oil?

Crude oil is a mixture of many different hydrocarbons (compounds containing only carbon and hydrogen). These hydrocarbons have different chain lengths and therefore different boiling points.

How It Works in Industry

1. Crude oil is heated to about 350 \u00b0C in a furnace until most of it turns to vapour.
2. The hot vapour enters a fractionating column (a tall tower).
3. The column is hot at the bottom and cool at the top.
4. As vapours rise up the column, they cool.
5. Each hydrocarbon condenses at the level where the temperature matches its boiling point.
6. Shorter-chain hydrocarbons (with lower boiling points) rise higher before condensing and are collected near the top.
7. Longer-chain hydrocarbons (with higher boiling points) condense lower down and are collected near the bottom.

Fractions of Crude Oil

Fraction	Carbon Chain Length	Boiling Point Range	Uses
Refinery gases	C\u2081–C\u2084	Below 25 \u00b0C	Heating, cooking (LPG)
Petrol (gasoline)	C\u2085–C\u2088	25–75 \u00b0C	Fuel for cars
Naphtha	C\u2088–C\u2081\u2082	75–180 \u00b0C	Chemical feedstock
Kerosene	C\u2081\u2082–C\u2081\u2085	180–250 \u00b0C	Jet fuel
Diesel	C\u2081\u2085–C\u2082\u2080	250–350 \u00b0C	Fuel for lorries, buses
Fuel oil	C\u2082\u2080–C\u2084\u2080	350–500 \u00b0C	Fuel for ships, power stations
Bitumen	C\u2084\u2080+	Above 500 \u00b0C	Roads, roofing

Trends in Crude Oil Fractions