GCSE OCR Gateway Organic Chemistry C6.2m Crude Oil

C6.2m To be able to recall that crude oil is a main source of hydrocarbons and is a feedstock for the petrochemical industry

Crude Oil

Crude oil is sometimes referred to as Petroleum.  

It is a black liquid of variable density and viscosity depending on the source of the oil. 

Oil found in Saudi Arabia tends to have a greater viscosity than that found under the North Sea.

 It occurs naturally usually underground in huge deposits of oil trapped in sand. 

The sand acts like a sponge holding water—squeeze it and the water is released.  Under compression from layers of rocks above, these underground deposits of oil bearing sand release their “black gold” of crude oil.

Oil deposits have been found to occur on land and under the seas. 

Analysis of crude oil has shown it to contain molecules called hydrocarbons.

Hydrocarbons are molecules that contain just the elements hydrogen (H) and carbon (C).

A typical hydrocarbon is methane CH₄. This is the simplest hydrocarbon.

Each carbon atom can form four covalent bonds with other atoms: in the case of methane, this is with hydrogen.

But as you will see carbon can also form covalent bonds with other atoms such as oxygen, nitrogen, phosphorus and halogens.  But most importantly for understanding crude oil carbon can form bonds with itself.

Carbon can form covalent bonds with itself.

This ability to bond to itself is unique to carbon.

Carbon atoms can form long strings or chains of atoms bonded to each other.

Carbon atoms can also form rings and cages of carbon atoms.

In crude oil, the majority of hydrocarbons found are carbon chains of varying lengths.

But these hydrocarbons have other properties.

They are usually saturated, that is the molecules only contain single covalent bonds.  No molecule contains any double or triple carbon carbon covalent bonds.

The formulae of these hydrocarbon molecules follow a simple pattern C_nH_2n+2

The number of hydrogen atoms in each hydrocarbon is twice that of the carbon atoms plus two. This pattern is known as the general formula of the hydrocarbon.

All hydrocarbon molecules whose formula fits this C_nH_2n+2 pattern are part of a family of molecules called Alkanes.

These alkane molecules are the feedstock of today’s petrochemical industry.

Feedstock is the material where all chemical processing begins.

All chemical processing is ultimately designed to change the feedstock molecules into something more useful to mankind.

So crude oil is processed into plastics, solvents, dyes, fertilisers, explosives via a series of intermediate stages, the fewer stages the better.