Crude Oil
Crude oil is a mixture of hydrocarbons. These chains can be super long or super short.
The Trend in Boiling Point and Viscosity
- Viscosity means how runny something is
- Volatile means how easy it turns into vapour at room temperature
As the number of carbon atoms in molecules increases and gets bigger, intermolecular attractions also increase, making it more difficult to pull one molecule away from neighbouring ones. As they get bigger, these changes occur:
- Boiling point increases – the larger the molecule, the higher the boiling point due to stronger intermolecular attractions.
- Liquids become less volatile – the bigger the hydrocarbon, the more slowly it evaporates in room temperature. This is again, due to strong intermolecular attractions.
- Liquids become more viscous (flow less easily) – Small hydrocarbons are runny, but large ones are much stickier and gooey (and viscous) because of intermolecular attractions.
- Bigger hydrocarbons do not burn as easily, meaning they are less useful.
The Fractionating Column
Crude oil is separated in fractionating column. This process is fractional distillation, and splits crude oil into various fractions depending on their boiling points and size.
Note: forget about Naphtha
| Fraction | Uses |
| Refinery gases | A mixture of methane, ethane, propane and butane.
Commonly used for domestic heating and cooking. |
| Gasoline | Cars |
| Kerosene | Used as fuel for jet aircraft.
As domestic heating oil. As ‘paraffin’ for small heaters and lamps. |
| Diesel oil | ü For buses, lorries, some cars and railway engines.
ü Some is cracked to produce more petrol. |
| Fuel oil | ü For ships
ü Industrial heating |
| Bitumen | ü Residue from the bottom which can be used for roads. |
Combustion and Incomplete Combustion
- Combustion of hydrocarbons produces carbon dioxide and water – exothermic.
- Incomplete combustion of hydrocarbons produces carbon monoxide and water – in which carbon monoxide is dangerous because it can bind to haemoglobin and prevent it from carrying oxygen.
In car engines, the temperature reached is high enough to allow nitrogen and oxygen from the air to react, forming nitrogen oxides. This contributes to smog and causes irritation to human mucus membranes. As well as that, nitrogen oxides can react with water in the atmosphere and from nitric acid – or acid rain.