Eduqas GCSE Chemistry 10 Carbon Compounds Exam Questions

About Eduqas GCSE Chemistry 10 Carbon Compounds

Carbon compounds is the organic chemistry topic in Eduqas GCSE Chemistry. It begins with crude oil as a finite resource, its separation by fractional distillation and the use of cracking to make smaller, more useful molecules and alkenes. You then study the homologous series of alkanes, alkenes, alcohols and carboxylic acids, their functional groups, formulae and typical reactions. The final part covers addition polymerisation, condensation polymers and naturally occurring polymers such as DNA, proteins and starch. Examiners often ask for the bromine water test, cracking equations, polymer repeating units and how boiling point changes with chain length.

What you need to know

• Crude oil and fractions Crude oil is a finite mixture of hydrocarbons formed from ancient biomass. Fractional distillation separates it into fractions with similar boiling points. Larger molecules have higher boiling points, are more viscous and less flammable.
• Alkanes and combustion Alkanes are saturated hydrocarbons, CnH2n+2, such as methane, ethane, propane and butane. Complete combustion produces carbon dioxide and water; incomplete combustion can produce carbon monoxide and soot.
• Cracking and alkenes Cracking breaks long-chain alkanes into shorter alkanes and alkenes using heat and a catalyst or steam, for example C10H22 → C8H18 + C2H4. Alkenes are unsaturated, CnH2n, with a C=C double bond, and decolourise bromine water.
• Alcohols Alcohols contain the -OH functional group: methanol, ethanol, propanol, butanol. Ethanol is made by fermentation of sugars with yeast or by hydration of ethene with steam. Alcohols burn as fuels and are used as solvents.
• Carboxylic acids Carboxylic acids contain -COOH, for example ethanoic acid. They are weak acids that react with carbonates to give carbon dioxide, and react with alcohols to form esters.
• Polymers Addition polymers form when many alkene monomers join, for example ethene to poly(ethene). Condensation polymers form from two different monomers with two functional groups, releasing a small molecule such as water. DNA, proteins, starch and cellulose are natural polymers.

Common mistakes in 10 Carbon Compounds

• Saying alkanes decolourise bromine water. Only alkenes, which are unsaturated, decolourise it; alkanes leave it orange.
• Drawing the repeating unit of poly(ethene) with a double bond. In the polymer the double bond has opened, so the repeat unit has single bonds and extension bonds through the brackets.
• Saying larger hydrocarbons have higher boiling points because the covalent bonds are stronger. It is because intermolecular forces are stronger between larger molecules.
• Writing cracking equations that do not balance. Check that the numbers of carbon and hydrogen atoms are equal on both sides.
• Confusing a fraction with a single compound. Each fraction is still a mixture of hydrocarbons with similar boiling points.

Try three 10 Carbon Compounds exam-style questions