Chemistry: Crude oil, cracking and hydrocarbons

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Crude oil: is a dark, smelly liquid which is a mixture containing two or more elements or compounds that are not chemically combined together.

Crude oil that comes straight out of the ground isnt much use. There are too many subtances in it, all with different boiling points. Before crude oil can be used, we have to separate mixtures of substances in crude oil by using distillation. Distillation separates liquids with different boiling points.

Most compounds in crude oil are made from atoms oj just two chemical elements- HYDROGEN AND CARBON. We call these compounds hydrocarbons. Most hydrocarbons in crude oil are alkanes.

Alkanes and Alkenes

The general formula for alkanes is CnH2n+2

Alkanes are described as being saturated hydrocarbons; mening that they conain as many hydrogen atoms as possilbe in each molecule. You cant add anymore


CH4 - Methane 

C2h6 - Ethane

As well as alkanes there is another type of hydrocaron known as alkenes. Unlike alkanes, alkenes are unsaturated molecules because they contain a dounble bond, other substances can add on to alkenes.

The general formula for alkenes is CnH2n


Ethene C2H4

Propene C3H6

Fractional Distillation: Separating crude oil.

The boiling points of a hydrocarbon depend on the size of its molecule. We can use the differenes in boiling points to separate the hydrocabons


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