Crude Oil: Answers

Describe how fractional distillation can separate hydrocarbons.

Fractional distillation separates hydrocarbons according to their boiling point. Longer hydrocarbons form more intermolecular forces so they have a higher boiling point. The hydrocarbons which make up crude oil are converted into a gas and added to a fractionating column which is hot at the bottom and cool at the top. The hydrocarbons rise up the column until they reach their boiling point, where they will condense into a liquid and can be drawn out from the column.

List the order of the fractions from the fraction containing the shortest hydrocarbons to the fraction containing the longest hydrocarbons.

Refinery gases, petrol / gasoline, kerosene, diesel, heavy fuel oil and bitumen. Use the saying ‘robot pirate killers don’t have belly buttons’ to help you remember the order.

What conditions are used for cracking?

Cracking uses temperatures of 600-700 degrees Celsius and a zeolite catalyst.

Why is cracking carried out?

Cracking is carried out because most of the hydrocarbons which make up crude oil tend to be longer-chain hydrocarbons. However, short-chain hydrocarbons make better fuels and are more in demand. Cracking is a process which converts long-chain alkanes into shorter-chain alkanes and alkenes.

Describe how polythene can be formed from lots of ethene monomers.

The double bond in ethene is broken and lots of these molecules are bonded together to form a long chain which is called poly(ethene) or polythene.