Alkenes/ Alkanes Flashcards
What is a hydrocarbon
- A molecule made up of hydrogen and carbon molecules only
- written as CnH2n+2
What are alkanes
Saturated hydrocarbons, with single covalent bonds
List the first 10 alkanes/enes
- meth
- eth
- prop
- but
- pent
- hex
- hept
- oct
- non
- dec
What are alkenes
- Non-saturated hydrocarbon, with a double covalent bond
- they can burn in the air
Describe how fractional distillation works
- crude oil is vaporised at the bottom of the fractional distillation tower
- it enters the column as vapour
- because of all the different boiling points of the hydrocarbons, they condense at different points
- larger hydrocarbons have higher boiling points, collected nearer bottom
- smaller hydrocarbons have lower boiling points, collected nearer top
- the smaller hydrocarbons are still gases and arn’t collected when the larger ones are
- some that don’t condese at 70 degrees come out of the tower as gases
What is the impurity found in coal
Sulpher
How is crude oil formed
Ancient plankton that is buried in the mud
Is crude oil finite
Yes
What are the hydrocarbons collected at the bottom for
- they are cheaper
- can be used for industrial oil, they evaporate at higher temps than short chain hydrocarbons
What can the hydrocarbons collected higher up be used for
- very expensive
- car petrol, they evaporate quickly
What is cracking
When we heat the heavy fractions collected in the distillation tower are thermally decomposed, meaning that we can break the larger hydrocarbons into smaller, more useful ones for an economic profit.
Why do we do cracking
- the main demmand for hydrocarbons are for fuels and starting materials for the chemical industry.
- larger hydrocarbons can’t be used to make that
- so we crack them to be smaller in order to be able to manufacture that stuff
- as a result we can get a larger profit.
How does cracking work
- larger fractions are heated to a vapour
- passed over a hot catalyst
- mixed with steam and heated to a high temp
- this means that thermal decomposition takes place
- the hydrocarbons are now cracked
How do you test for alkenes
- add it to bromine water
- alkenes will make the orange bromine water turn colourless because the bromine reacts with it.
- the double bonds break and accepts the bromine molecule
- alkanes won’t change the orange colour
What is crude oil
A complex mixture of hydrocarbons
