GCSE Chemistry₈₄₆₂

Crude oil is a finite resource found in rocks. Crude oil is the remains of an ancient biomass consisting mainly of plankton that was buried in mud.

Crude oil is a mixture of a very large number of compounds. Most of the compounds in crude oil are hydrocarbons, which are molecules made up of hydrogen and carbon atoms only.

Most of the hydrocarbons in crude oil are hydrocarbons called alkanes. The general formula for the homologous series of alkanes is C_n H_2n+2

The first four members of the alkanes are methane, ethane, propane and butane.

Alkane molecules can be represented in the following forms:

C₂ H₆ or

Students should be able to recognise substances as alkanes given their formulae in these forms.

Students do not need to know the names of specific alkanes other than methane, ethane, propane and butane.

WS 1.2

Make models of alkane molecules using the molecular modelling kits.

The many hydrocarbons in crude oil may be separated into fractions, each of which contains molecules with a similar number of carbon atoms, by fractional distillation.

The fractions can be processed to produce fuels and feedstock for the petrochemical industry.

Many of the fuels on which we depend for our modern lifestyle, such as petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases, are produced from crude oil.

Many useful materials on which modern life depends are produced by the petrochemical industry, such as solvents, lubricants, polymers, detergents.

The vast array of natural and synthetic carbon compounds occur due to the ability of carbon atoms to form families of similar compounds.

Students should be able to explain how fractional distillation works in terms of evaporation and condensation.

Knowledge of the names of other specific fractions or fuels is not required.

WS 1.2

Some properties of hydrocarbons depend on the size of their molecules, including boiling point, viscosity and flammability. These properties influence how hydrocarbons are used as fuels.

Students should be able to recall how boiling point, viscosity and flammability change with increasing molecular size.

The combustion of hydrocarbon fuels releases energy. During combustion, the carbon and hydrogen in the fuels are oxidised. The complete combustion of a hydrocarbon produces carbon dioxide and water.

Students should be able to write balanced equations for the complete combustion of hydrocarbons with a given formula.

Knowledge of trends in properties of hydrocarbons is limited to:

• boiling points
• viscosity
• flammability.

WS 1.2, 4.1

Investigate the properties of different hydrocarbons.

Hydrocarbons can be broken down (cracked) to produce smaller, more useful molecules.

Cracking can be done by various methods including catalytic cracking and steam cracking.

Students should be able to describe in general terms the conditions used for catalytic cracking and steam cracking.

The products of cracking include alkanes and another type of hydrocarbon called alkenes.

Alkenes are more reactive than alkanes and react with bromine water, which is used as a test for alkenes.

Students should be able to recall the colour change when bromine water reacts with an alkene.

There is a high demand for fuels with small molecules and so some of the products of cracking are useful as fuels.

Alkenes are used to produce polymers and as starting materials for the production of many other chemicals.

Students should be able to balance chemical equations as examples of cracking given the formulae of the reactants and products.

Students should be able to give examples to illustrate the usefulness of cracking. They should also be able to explain how modern life depends on the uses of hydrocarbons.

(For Combined Science: Trilogy and Synergy students do not need to know the formulae or names of individual alkenes.)

WS 1.2

Alkenes are hydrocarbons with a double carbon-carbon bond. The general formula for the homologous series of alkenes is C_n H_2n

Alkene molecules are unsaturated because they contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms.

The first four members of the homologous series of alkenes are ethene, propene, butene and pentene.

Alkene molecules can be represented in the following forms:

C₃ H₆

or

Students do not need to know the names of individual alkenes other than ethene, propene, butene and pentene.

WS 1.2

Recognise substances that are alkenes from their names or from given formulae in these forms.

MS 5b

Visualise and represent 2D and 3D forms including two- dimensional representations of 3D objects.

Alkenes are hydrocarbons with the functional group C=C.

It is the generality of reactions of functional groups that determine the reactions of organic compounds.

Alkenes react with oxygen in combustion reactions in the same way as other hydrocarbons, but they tend to burn in air with smoky flames because of incomplete combustion.

Alkenes react with hydrogen, water and the halogens, by the addition of atoms across the carbon-carbon double bond so that the double bond becomes a single carbon-carbon bond.

Students should be able to:

• describe the reactions and conditions for the addition of hydrogen, water and halogens to alkenes
• draw fully displayed structural formulae of the first four members of the alkenes and the products of their addition reactions with hydrogen, water, chlorine, bromine and iodine.

Alcohols contain the functional group –OH.

Methanol, ethanol, propanol and butanol are the first four members of a homologous series of alcohols.

Alcohols can be represented in the following forms:

CH₃ CH₂ OH

or

Students should be able to:

• describe what happens when any of the first four alcohols react with sodium, burn in air, are added to water, react with an oxidising agent
• recall the main uses of these alcohols.

Aqueous solutions of ethanol are produced when sugar solutions are fermented using yeast.

Students should know the conditions used for fermentation of sugar using yeast.

Students should be able to recognise alcohols from their names or from given formulae.

Students do not need to know the names of individual alcohols other than methanol, ethanol, propanol and butanol.

Students are not expected to write balanced chemical equations for the reactions of alcohols other than for combustion reactions.

AT 2, 5, 6

Opportunities when investigating reactions of alcohols.

Carboxylic acids have the functional group –COOH.

The first four members of a homologous series of carboxylic acids are methanoic acid, ethanoic acid, propanoic acid and butanoic acid.

The structures of carboxylic acids can be represented in the following forms:

CH₃ COOH

or

Students should be able to:

• describe what happens when any of the first four carboxylic acids react with carbonates, dissolve in water, react with alcohols
• (HT only) explain why carboxylic acids are weak acids in terms of ionisation and pH (see Strong and weak acids (HT only) ).

Students should be able to recognise carboxylic acids from their names or from given formulae.

Students do not need to know the names of individual carboxylic acids other than methanoic acid, ethanoic acid, propanoic acid and butanoic acid.

Students are not expected to write balanced chemical equations for the reactions of carboxylic acids.

Students do not need to know the names of esters other than ethyl ethanoate.

AT 2, 5, 6

Opportunities within investigation of the reactions of carboxylic acids.

Alkenes can be used to make polymers such as poly(ethene) and poly(propene) by addition polymerisation.

In addition polymerisation reactions, many small molecules (monomers) join together to form very large molecules (polymers).

For example:

In addition polymers the repeating unit has the same atoms as the monomer because no other molecule is formed in the reaction.

WS 1.2

Use models to represent addition polymerisation.

Students should be able to:

• recognise addition polymers and monomers from diagrams in the forms shown and from the presence of the functional group C=C in the monomers
• draw diagrams to represent the formation of a polymer from a given alkene monomer
• relate the repeating unit to the monomer.

MS 5b

Visualise and represent 2D and 3D forms including two-dimensional representations of 3D objects.

Condensation polymerisation involves monomers with two functional groups. When these types of monomers react they join together, usually losing small molecules such as water, and so the reactions are called condensation reactions.

The simplest polymers are produced from two different monomers with two of the same functional groups on each monomer.

For example:

ethanediol

and

hexanedioic acid

polymerise to produce a polyester:

WS 1.2

Use models to represent condensation polymerisation.

MS 5b

Visualise and represent 2D and 3D forms including two-dimensional representations of 3D objects.

Amino acids have two different functional groups in a molecule. Amino acids react by condensation polymerisation to produce polypeptides.

For example: glycine is H₂ NCH₂ COOH and polymerises to produce the polypeptide

Different amino acids can be combined in the same chain to produce proteins.

DNA (deoxyribonucleic acid) is a large molecule essential for life. DNA encodes genetic instructions for the development and functioning of living organisms and viruses.

Most DNA molecules are two polymer chains, made from four different monomers called nucleotides, in the form of a double helix. Other naturally occurring polymers important for life include proteins, starch and cellulose.

Students should be able to name the types of monomers from which these naturally occurring polymers are made.