OCR GCSE Chemistry A C6.2 Organic Chemistry Exam Questions

About OCR GCSE Chemistry A C6.2 Organic Chemistry

C6.2 introduces the chemistry of carbon compounds. On the OCR Gateway Chemistry A course it is part of Topic C6 Global challenges, assessed in Paper 2 (Foundation) or Paper 4 (Higher). You study crude oil as a source of fuels and feedstock, the homologous series of alkanes, alkenes, alcohols and carboxylic acids, and how polymers are made. It builds on covalent bonding in C2.2, separation in C2.1 and energetics in C3.2, and links to the atmosphere in C6.3. Examiners frequently test general formulae, the bromine water test, fractional distillation and cracking, addition reactions of alkenes, and drawing repeat units of polymers.

What you need to know

• Crude oil Crude oil is a finite mixture of hydrocarbons separated by fractional distillation. Fractions with longer chains have higher boiling points, are more viscous and less flammable, and condense lower down the column.
• Cracking Cracking breaks long-chain alkanes into shorter, more useful alkanes and alkenes using heat and a catalyst. For example, C10H22 -> C8H18 + C2H4.
• Alkanes and alkenes Alkanes (CnH2n+2) are saturated and contain only single bonds. Alkenes (CnH2n) are unsaturated with a C=C double bond; they decolourise orange bromine water and undergo addition reactions with hydrogen, water and halogens.
• Alcohols and carboxylic acids Alcohols contain the -OH group, burn as fuels and can be oxidised to carboxylic acids. Carboxylic acids contain -COOH, are weak acids and react with carbonates to produce carbon dioxide.
• Addition polymers Alkene monomers join together when their double bonds open to form a long chain, for example ethene forms poly(ethene). You should draw a repeat unit from a monomer and the monomer from a repeat unit.
• Condensation and natural polymers Condensation polymerisation joins monomers with two functional groups and releases a small molecule such as water, for example polyesters. Natural polymers include DNA (from nucleotides), proteins (from amino acids) and carbohydrates such as starch and cellulose (from sugars).

Common mistakes in C6.2 Organic Chemistry

• Saying the bromine water test makes alkenes go colourless. It is the bromine water that changes from orange to colourless.
• Using 'clear' to mean colourless. Clear means transparent; the correct observation is colourless.
• Drawing a polymer repeat unit with the double bond still present. The C=C becomes a single bond and extension bonds go through the brackets.
• Writing that fractional distillation separates individual compounds. It separates crude oil into fractions, each a mixture with similar boiling points.
• Getting general formulae wrong, for example writing CnH2n for alkanes. Alkanes are CnH2n+2 and alkenes are CnH2n.

Try three C6.2 Organic Chemistry exam-style questions