Fractional distillation and crackingAQA A-Level Chemistry: Mind map

Exam questions on Fractional distillation and cracking

1. A refinery separates crude oil in a fractionating column. The fractions collected, in no particular order, are refinery gas, petrol, kerosene, diesel and fuel oil. Each fraction is a mixture of alkanes.
   Explain why alkanes are described as saturated hydrocarbons.2 marks
2. Tetradecane, C₁₄H₃₀, is a long-chain alkane that is cracked in an oil refinery. Cracking breaks C–C bonds in long-chain alkanes to form shorter, more useful molecules.
   Write an equation for the cracking of tetradecane to form octane and ethene as the only products.2 marks
3. An oil refinery has a large surplus of long-chain hydrocarbons from fractional distillation. At the same time, demand for petrol and for alkenes used in the chemical industry is greater than the amounts the distillation alone provides.
   Explain the economic reasons for cracking long-chain alkanes.3 marks