A fraction is a group of hydrocarbons whose boiling points lie within a similar range.

Describe the temperature gradient inside a fractionating column.

The column is hottest at the bottom and becomes steadily cooler towards the top.

Explain why different fractions condense at different heights in a fractionating column.

Each fraction condenses where the temperature falls below its boiling point, so fractions with higher boiling points condense lower down.

Explain why the substances collected at the top of a fractionating column have small molecules.

Small molecules have weak forces between them and low boiling points, so they stay as vapour until they reach the cool top of the column.

Edexcel GCSE Combined Science Chemistry 1SC0

Key Concepts in Chemistry

Topic overview Formulae, word equations and balanced equations Hazard symbols and assessing risk The changing model of the atom Protons, neutrons and electrons The nucleus, mass number and atomic mass Elements and isotopes Calculating particle numbers and relative atomic mass Mendeleev's periodic table How the modern periodic table is arranged Electronic configuration and the periodic table How ionic bonds form Ions in ionic compounds Formulae of ionic compounds and ionic equations Naming compounds and the ionic lattice Covalent bonds and molecules Dot and cross diagrams for simple molecules Classifying substances and the properties of ionic compounds Properties of simple molecular substances, and forms of carbon Graphite and diamond Fullerenes and graphene Polymers and models of bonding The properties of metals Relative formula mass and percentage composition Empirical and molecular formulae Conservation of mass in closed and open systems Reacting masses from balanced equations Concentration in grams per cubic decimetre Moles and the Avogadro constant Limiting reactants and stoichiometry

States of Matter and Mixtures

Topic overview The three states of matter and changes of state Energy changes during changes of state, and predicting state Pure substances and melting point data Choosing a separation technique Separating a mixture in practice Paper chromatography and interpreting a chromatogram Investigating inks by distillation and chromatography Making water potable

Chemical Changes

Topic overview Acids, alkalis and the pH scale Indicators: litmus, methyl orange and phenolphthalein Hydrogen ion concentration and the pH scale Investigating pH change when neutralising an acid Dilute and concentrated, weak and strong acids Bases and alkalis Reactions of acids, and testing for hydrogen and carbon dioxide Neutralisation and its ionic equation Preparing soluble salts from insoluble and soluble reactants Preparing pure, dry copper sulfate crystals Carrying out an acid-alkali titration Solubility rules Predicting precipitates and preparing an insoluble salt Electrolytes and what electrolysis is Movement of ions and predicting the products of molten electrolysis Electrolysis with inert electrodes Writing half equations Oxidation and reduction at the electrodes Electrolysis of copper sulfate solution Investigating the electrolysis of copper sulfate

Extracting Metals and Equilibria

Topic overview Investigating the reactivity of metals Displacement reactions as redox reactions The reactivity series Ores, oxidation and reduction Choosing a method to extract a metal Biological methods of metal extraction Corrosion resistance and recycling metals Life cycle assessment Reversible reactions and dynamic equilibrium The Haber process and its conditions Changing the position of an equilibrium

Groups in the Periodic Table

Topic overview The groups of the periodic table, and the alkali metals Reactions of the alkali metals with water The pattern in alkali metal reactivity and why it happens Physical properties of the halogens The test for chlorine, and halogens reacting with metals Hydrogen halides, and explaining halogen reactivity Displacement reactions of the halogens Group 0: the noble gases

Rates of Reaction and Energy Changes

Topic overview Investigating the rate of a reaction Measuring rate and interpreting rate graphs Collision theory and factors affecting rate Catalysts and enzymes Exothermic and endothermic changes Bond breaking, bond making and the overall energy change Bond energies, activation energy and reaction profiles

Fuels and Earth Science

Topic overview Hydrocarbons and crude oil Fractional distillation and the fractions Properties of the fractions and homologous series Complete and incomplete combustion Carbon monoxide and soot Pollutants and acid rain Hydrogen and fossil fuels compared Cracking and why it is necessary The Earth's early atmosphere How the oceans formed and how oxygen appeared The test for oxygen and the greenhouse gases Today's atmosphere and evidence for climate change

Fuels and Earth Science

Fractional distillation and the fractions

3 things to know
Paper 4

Overview

What a fraction is, how crude oil is vaporised and separated in a fractionating column with its temperature gradient, why fractions condense at different heights and are still mixtures, and the order and uses of gases, petrol, kerosene, diesel oil, fuel oil and bitumen.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

Name the process used to separate crude oil into simpler, more useful mixtures.

Key term

What is a fraction?

Process

Describe the first stage in the fractional distillation of crude oil.

Questions from this subtopic

Each one with the model answer underneath.

1
Name the process used to separate crude oil into simpler, more useful mixtures.
Model answer
Crude oil is separated by fractional distillation.
2
What is a fraction?
Model answer
A fraction is a group of hydrocarbons whose boiling points lie within a similar range.
3
Describe the first stage in the fractional distillation of crude oil.
Model answer
The crude oil is heated until it evaporates, and the vapour is fed into a tall fractionating column.
4
Describe the temperature gradient inside a fractionating column.
Model answer
The column is hottest at the bottom and becomes steadily cooler towards the top.
5
Explain why different fractions condense at different heights in a fractionating column.
Model answer
Each fraction condenses where the temperature falls below its boiling point, so fractions with higher boiling points condense lower down.
6
Explain why the substances collected at the top of a fractionating column have small molecules.
Model answer
Small molecules have weak forces between them and low boiling points, so they stay as vapour until they reach the cool top of the column.

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Key Concepts in Chemistry

States of Matter and Mixtures

Chemical Changes

Extracting Metals and Equilibria

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Hydrogen is formed.

chloridebromideiodide

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