Alkanes and structural isomerismEdexcel International A Level Chemistry: Mind map

Exam questions on Alkanes and structural isomerism

1. Petrol is a mixture of hydrocarbons including pentane, octane and cyclohexane. A refinery chemist classifies each of these compounds as an alkane or a cycloalkane.
   Explain what is meant by the terms 'hydrocarbon' and 'saturated' when they are applied to octane.2 marks
2. Pentane, C₅H₁₂, is a liquid in petrol that boils at 36 °C. A refinery sample of C₅H₁₂ is found to contain two other compounds with the same molecular formula, which boil at 28 °C and 10 °C.
   Explain why the compound that boils at 28 °C, 2-methylbutane, is a structural isomer of pentane.2 marks
3. A hydrocarbon X is found in petrol. Analysis shows that it contains 83.3% carbon and 16.7% hydrogen by mass, and its relative molecular mass is 72.0. X does not decolourise bromine water and contains no carbon–carbon double bonds.
   Use the data to deduce the empirical formula and the molecular formula of X, showing your working.3 marks