Hydrocarbons from crude oil Flashcards
What is crude oil?
Crude oil is a fossil fuel. It comes from plants and animals that started decaying millions of years ago.
Whats in crude oil?
Crude oil is a mixture of over 150 different hydrocarbons, most of which are unbranched alkanes.
Define fractional distillation
Fractional distillation is the separation of the components in a liquid mixture into fractions which differ in boiling point by means of distillation, typically using a fractionating column.
Explain the steps of fractional distillation.
The crude oil is first vaporised by heating and is then passed into the fractionating column. The column is hotter at the bottom than at the top, and gasses pass up the column through a series of bubble caps. Eventually the gases reach a temperature that is lower than their boiling points. Here, the vapour condenses to a liquid. The liquid fractions are then tapped off into storage containers.
Describe what is in the storage containers after the crude oil has gone through fractional distillation and how they got their due to their properties?
1) Short-chained hydrocarbons with lower boiling points condense near the top of the column
2) Longer-chained hydrocarbons with higher boiling points condense nearer to the bottom.
3) Gases do not condense and pass through an outlet at the top of the column as “petroleum gas”.
4) The residue from the process is bitumen, which is removed from the bottom of the column
What is the effect of chain length and how is it useful in separating alkanes?
As the chain length increases, the boiling point increases because the intermolecular forces between the molecules get stronger. In a longer-chained alkane, there are more points of contact between the molecules leading to more van der Waals’ forces between molecules. It takes more energy, and therefore a higher temperature, to seperate the molecules. This allows the different alkanes in crude oil to be seperated by their boiling points.
What is the effect of branching and how is it useful in separating alkanes?
Isomers of alkanes have the same molecular mass. A branched isomer has a lower boiling point than the unbranched isomer. In a branched alkane, there are fewer points of contact between molecules, leading to fewer van der Waals’ forces between molecules. Also, branched molecules cannot get as close to each other as unbranched ones, thus decreasing intermolecular forces between molecules. There, less energy(heat) is required to separate the molecules.
What sort of alkanes are used in fuels?
Short-chain alkanes are valuable as clean fuels.
- Methane is used as natural gas for domestic heating and cooking
- Propane and butane are liquefied and used as fuel for cars.
- Octane is present in petrol,used to fuel the internal combustion engine.
What is carbon monoxide and what is its disadvantages?
- Carbon monoxide is a colourless,odourless gas. It is produced when any fossil fuel is burned with an insufficient supply of oxygen.
- Carbon monoxide is poisonous. It prevents the haemoglobin in red blood cells from binding with oxygen and the body’s tissue become starved of oxygen.
Define cracking
Cracking refers to the breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes.
Define catalyst
A catalyst is a substance that increases the rate of a chemical reaction without being used up in the process.
What process changes unbranched alkanes into branched alkanes?
The process is called isomerisation.
What is the name of the process that converts aliphatic hydrocarbons into cyclic or aromatic hydrocarbons?
The process is known as reforming.
Why are branched and cyclic alkanes important chemical additives?
They promote more efficient combustion than straight-chain alkanes.
What is 90% of the crude oil used for?
Source of fuel
