OCR GCSE Combined Science Chemistry J250

Chemical Reactions

Topic overview Writing formulae of elements and compounds Balanced equations, and deducing formulae from ions Ionic equations, and state symbols The mole and the Avogadro constant Conservation of mass, and changes of mass in open systems Stoichiometry, and calculating reacting masses Exothermic and endothermic reactions, and reaction profiles Activation energy, and bond energy calculations Oxidation and reduction, by oxygen and by electrons Acids, alkalis and neutralisation The ionic equation for neutralisation, and reactions of acids Dilute and concentrated, weak and strong The pH scale, and hydrogen ion concentration pH as a factor of ten, and measuring pH Products at the electrodes, and molten ionic compounds Electrolysis of aqueous solutions Inert and non-inert electrodes

Elements, Compounds and Mixtures

Topic overview Purity, and melting point data Relative formula mass and empirical formulae Formulations, and separating mixtures Paper and thin layer chromatography Interpreting chromatograms and Rf values Choosing a purification method Metals and non-metals in the Periodic Table Electron arrangement and position in the Periodic Table Ionic, covalent and metallic bonding compared Dot and cross diagrams, and the limits of models Reactions, electron arrangement and Mendeleev's table Carbon's four bonds, and the variety of organic compounds Diamond, graphite, fullerenes and graphene Bond strength, intermolecular forces and predicting state Bulk properties of ionic, molecular and giant structures

Global Challenges

Topic overview Extracting metals by reduction and by electrolysis Biological methods of metal extraction Life cycle assessment Recycling, and the decisions behind it Fractional distillation of crude oil The fractions, and crude oil as a feedstock Dependence on hydrocarbons, and cracking The Earth's early atmosphere, and how oxygen developed The greenhouse effect, and evidence for climate change Effects of carbon dioxide and methane, and air pollutants Producing potable water

Monitoring and Controlling Chemical Reactions

Topic overview Mass of solute, concentration and dilution calculations Measuring the rate of a reaction, and rate graphs Factors affecting rate, and collision theory Surface area and rate Catalysts and how they work Reversible reactions and dynamic equilibrium Changing the conditions of an equilibrium Activation energy, and enzymes as catalysts

Particles

Topic overview The particle model and changes of state Limitations of the particle model How the atomic model changed, and the structure of the atom The size of atoms, and the subatomic particles Calculating protons, neutrons and electrons

Predicting and Identifying Reactions

Topic overview Groups 1, 7 and 0, and why they behave as they do Predicting reactivity from the Periodic Table Reactivity of metals with water and acids Tests for oxygen, hydrogen, carbon dioxide and chlorine

Global Challenges

The fractions, and crude oil as a feedstock

3 things to know
Paper 10 (Chemistry)

Overview

The alkanes and their general formula CₙH₂ₙ₊₂, what a hydrocarbon is, working out and naming alkane formulae such as C₈H₁₈ and pentane, what saturated means, why a fraction is not pure, crude oil as the feedstock of the petrochemical industry for polymers, solvents, lubricants and medicines, how crude oil formed, and ethene for poly(ethene).

What you need to know

Answer each one before you reveal it.

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Key term

What is a hydrocarbon?

Numbers

An alkane molecule contains twenty hydrogen atoms. How many carbon atoms does it contain?

Key term

What is meant by a feedstock?

Questions from this subtopic

Each one with the model answer underneath.

1
Most of the compounds in a fraction of crude oil fit which general formula?
Model answer
CₙH₂ₙ₊₂.
2
Which homologous series makes up most of the compounds in the fractions of crude oil?
Model answer
The alkanes.
3
What is a hydrocarbon?
Model answer
A compound made from hydrogen and carbon atoms only.
4
Give the formula of the alkane whose molecules contain eight carbon atoms.
Model answer
C₈H₁₈.
5
An alkane molecule contains twenty hydrogen atoms. How many carbon atoms does it contain?
Model answer
Nine, because 2 × 9 + 2 = 20, giving the formula C₉H₂₀.
6
Name the alkane with the formula C₅H₁₂.
Model answer
Pentane.

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Chemical Reactions

Elements, Compounds and Mixtures

Global Challenges

Monitoring and Controlling Chemical Reactions

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AMetals are on the left and in the centre, and non-metals are on the right-hand side.

BKI, because potassium loses one electron and iodine gains one.

CCaCl₂, because a calcium atom loses two electrons and each chlorine atom gains one.

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Sodium ions give a bright yellow flame colour.

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The fractions, and crude oil as a feedstock

Overview

What you need to know

What is a hydrocarbon?

An alkane molecule contains twenty hydrogen atoms. How many carbon atoms does it contain?

What is meant by a feedstock?

Questions from this subtopic

Most of the compounds in a fraction of crude oil fit which general formula?

Which homologous series makes up most of the compounds in the fractions of crude oil?

What is a hydrocarbon?

Give the formula of the alkane whose molecules contain eight carbon atoms.

An alkane molecule contains twenty hydrogen atoms. How many carbon atoms does it contain?

Name the alkane with the formula C₅H₁₂.

Other ways to work this

What is inside Levo

See a huge jump in your memorisation

Cram a whole paper in one sitting

Blank Blitz consolidates the facts

Build It trains answer structure

Test It catches misconceptions

Brain Breaks between sessions

Every question in Global Challenges, on a schedule.