Chemguide: Support for CIE A level Chemistry

This statement is about using crude oil as a source of hydrocarbons. It uses the words "aliphatic" and "aromatic" hydrocarbons that you may not be familiar with.

Aliphatic hydrocarbons are the hydrocarbons that you will have met so far, containing chains (which may be branched) of carbon atoms. Aromatic hydrocarbons contain benzene rings - rings of carbon atoms with delocalised electrons. These may have hydrocarbon chains attached to them. If you haven't come across any aromatic compounds yet, don't worry about it for now.

Before you go on, you should find and read the statement in your copy of the syllabus.

There is nothing on Chemguide about the fractional distillation of crude oil, and I don't intend to add anything now. At the time of writing (August 2013), CIE had only asked a trivial question on this statement ("Explain what is meant by fractional distillation" wanting the answer "separation of compounds by their boiling points"). It is hard to see why they would waste space in an exam by asking very much about this. There is a lot of other organic chemistry that it is more important for them to test.

You will almost certainly have covered this in enough detail at an earlier level (O level or GCSE or an equivalent), and so I have got two suggestions.

• Go back to your old notes (if you still have them) and read about crude oil fractional distillation again.

• Do a Google search on fractional distillation crude oil, and find a simple description that you feel comfortable with. Don't worry if every single site that you look at gives you different information - this particular topic is a complete nightmare in that respect.

  This page from the BBC has a simple, but reasonably accurate diagram and easy to read text. But try some other sites if you like.

The syllabus mentions crude oil as a source of aromatic hydrocarbons. Remember that an aromatic hydrocarbon is one containing a benzene ring.

Crude oil is mainly a mixture of chains of carbon atoms. Some of these can be made into rings by a process called reforming. If you follow this link, you will find this explained towards the bottom of the page. There is no hint from existing past papers that CIE will want this, but it is perhaps better to be safe than sorry.

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