Reactions of alkenes and alcohols (chemistry only) revision notes

Reactions of alkenes and alcohols (chemistry only)

This AQA GCSE Chemistry 8462 Unit 4.7 Organic chemistry guide focuses on Reactions of alkenes and alcohols (chemistry only). It is built from approved learning objectives in Organic chemistry and keeps formulae, reactions, properties, and organic families separate.

What this topic covers

• Structure and formulae of alkenes: 7 approved learning objectives.
• Reactions of alkenes: 5 approved learning objectives.
• Alcohols: 13 approved learning objectives.
• Carboxylic acids: 8 approved learning objectives.
• Polymerisation and naturally occurring polymers: 19 approved learning objectives.

Core revision points

• Represent alkene molecules in displayed, structural and molecular formula forms. In exam answers, connect this point to Structure and formulae of alkenes and use precise organic chemistry language.
• Recognise alkenes from their names or from given formulae. In exam answers, connect this point to Structure and formulae of alkenes and use precise organic chemistry language.
• State the general formula for the homologous series of alkenes as CnH2n. In exam answers, connect this point to Structure and formulae of alkenes and use precise organic chemistry language.
• Recall the first four members of the homologous series of alkenes as ethene, propene, butene and pentene. In exam answers, connect this point to Structure and formulae of alkenes and use precise organic chemistry language.
• Describe alkenes as hydrocarbons with a double carbon-carbon bond. In exam answers, connect this point to Structure and formulae of alkenes and use precise organic chemistry language.
• Explain that alkenes are unsaturated because they contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms. In exam answers, connect this point to Structure and formulae of alkenes and use precise organic chemistry language.
• Visualise and represent 2D and 3D forms of alkene molecules. (MS 5b) In exam answers, connect this point to Structure and formulae of alkenes and use precise organic chemistry language.
• Describe the reactions and conditions for the addition of hydrogen, water and halogens to alkenes. In exam answers, connect this point to Reactions of alkenes and use precise organic chemistry language.
• Explain that alkenes react with oxygen in combustion reactions in the same way as other hydrocarbons. In exam answers, connect this point to Reactions of alkenes and use precise organic chemistry language.
• Explain that alkenes react with hydrogen, water and halogens by addition across the carbon-carbon double bond. In exam answers, connect this point to Reactions of alkenes and use precise organic chemistry language.
• 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. In exam answers, connect this point to Reactions of alkenes and use precise organic chemistry language.
• Explain that alkenes tend to burn in air with smoky flames because of incomplete combustion. In exam answers, connect this point to Reactions of alkenes and use precise organic chemistry language.
• Represent alcohols in displayed, structural and molecular formula forms. In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Describe what happens when any of the first four alcohols burn in air. In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Describe what happens when any of the first four alcohols are added to water. In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Describe what happens when any of the first four alcohols react with an oxidising agent. In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Recall the main uses of these alcohols. In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Recognise alcohols from their names or from given formulae. In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Write balanced equations for combustion reactions of alcohols. In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Describe alcohols as compounds that contain the functional group –OH. In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Recall the first four members of a homologous series of alcohols as methanol, ethanol, propanol and butanol. In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Describe what happens when any of the first four alcohols react with sodium. In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Investigate reactions of alcohols. (AT 2, 5, 6) In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Know the conditions used for fermentation of sugar using yeast. In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Explain that aqueous solutions of ethanol are produced when sugar solutions are fermented using yeast. In exam answers, connect this point to Alcohols and use precise organic chemistry language.
• Explain why carboxylic acids are weak acids in terms of ionisation and pH. (HT only) In exam answers, connect this point to Carboxylic acids and use precise organic chemistry language.
• Describe carboxylic acids as compounds that contain the functional group –COOH. In exam answers, connect this point to Carboxylic acids and use precise organic chemistry language.
• Recall the first four members of a homologous series of carboxylic acids as methanoic acid, ethanoic acid, propanoic acid and butanoic acid. In exam answers, connect this point to Carboxylic acids and use precise organic chemistry language.
• Describe what happens when any of the first four carboxylic acids react with carbonates. In exam answers, connect this point to Carboxylic acids and use precise organic chemistry language.
• Describe what happens when any of the first four carboxylic acids dissolve in water. In exam answers, connect this point to Carboxylic acids and use precise organic chemistry language.
• Recognise carboxylic acids from their names or from given formulae. In exam answers, connect this point to Carboxylic acids and use precise organic chemistry language.
• Represent carboxylic acids in displayed, structural and molecular formula forms. In exam answers, connect this point to Carboxylic acids and use precise organic chemistry language.
• Describe what happens when any of the first four carboxylic acids react with alcohols. In exam answers, connect this point to Carboxylic acids and use precise organic chemistry language.
• Amino acids have two different functional groups in a molecule. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• When these monomers react they join together, usually losing small molecules such as water, so the reactions are called condensation reactions. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• Different amino acids can be combined in the same chain to produce proteins. (HT only) In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• Amino acids react by condensation polymerisation to produce polypeptides. (HT only) In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• DNA is a large molecule essential for life. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• Other naturally occurring polymers important for life include proteins, starch and cellulose. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• Alkenes can be used to make polymers such as poly(ethene) and poly(propene) by addition polymerisation. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• Recognise addition polymers and monomers from diagrams and from the presence of the C=C functional group in the monomers. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• Explain the basic principles of condensation polymerisation by reference to the functional groups in the monomers and the repeating units in the polymers. (HT only) In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• Glycine polymerises to produce a polypeptide. (HT only) In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• DNA encodes genetic instructions for the development and functioning of living organisms and viruses. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• Name the types of monomers from which these naturally occurring polymers are made. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• In addition polymers, the repeating unit has the same atoms as the monomer because no other molecule is formed in the reaction. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• Relate the repeating unit to the monomer. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• The simplest polymers are produced from two different monomers with two of the same functional groups on each monomer. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• In addition polymerisation reactions, many small molecules (monomers) join together to form very large molecules (polymers). In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• Draw diagrams to represent the formation of a polymer from a given alkene monomer. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• Condensation polymerisation involves monomers with two functional groups. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.
• Most DNA molecules are two polymer chains, made from four different monomers called nucleotides, in the form of a double helix. In exam answers, connect this point to Polymerisation and naturally occurring polymers and use precise organic chemistry language.

Formula and structure checks

Use molecular formulae to show atom counts, structural formulae to show how atoms are arranged, displayed formulae only when a diagram renderer is available, and general formulae such as CnH2n+2 or CnH2n only for the correct homologous series.

Concept boundaries

Keep molecular formula, structural formula, displayed formula, and general formula distinct. Do not confuse alkanes with alkenes, saturated with unsaturated, cracking with combustion, polymers with monomers, or hydrocarbons with oxygen-containing alcohols and carboxylic acids. When formulae are used, preserve the stored notation exactly and explain the GCSE chemistry idea in words rather than using unsupported displayed-formula diagrams.

Key terms

• molecular formula
• alkene
• functional group
• homologous series
• double bond
• unsaturated
• 2D and 3D representation
• addition reaction
• combustion
• incomplete combustion
• smoky flame
• Alcohol
• Displayed formula
• Combustion of alcohols
• Flame temperature of alcohols
• Water
• alcohol
• oxidising agent
• uses of alcohols
• Functional group
• Combustion
• sodium reaction
• yeast
• fermentation

Exam practice advice

When answering questions, name the organic family, state the formula type, describe the reaction or property, and then connect the evidence back to the learning objective. If a question asks about cracking, focus on forming smaller hydrocarbons and alkenes; if it asks about combustion, focus on oxidation to carbon dioxide and water. If a question asks about polymers, keep monomers and repeat units distinct.