Paper 2 General Flashcards
Shorter hydrocarbons are more volatile what does this mean?
They have lower boiling points
Longer hydrocarbons are more viscous, what does this mean?
More thick and gloopy
As the chain length (number of carbon atoms) of alkanes increases, they become more or less flammable?
Less
What is the word equation for the complete combustion of a hydrocarbon?
hydrocarbon + oxygen ➔ carbon dioxide + water
Alkanes are a homologous series of molecules that contain:
Only carbon and hydrogen atoms.
Only single bonds (alkanes have no double bonds)
What is the general formula for alkanes?
CnH2n+2
What is another way to describe hydrocarbons with only single bonds?
Saturated
How fractional distillation works:
- Crude oil is a mixture of hydrocarbons with different boiling points.
- The first step is to heat the crude oil to a very high temperature so that all of the compounds are evaporated from liquid to gas.
- The hot gaseous hydrocarbons then rise up the fractionating column (because hot gas rises).
- As they rise, they cool down, because the top of the column is cooler than the bottom.
- The hydrocarbons will condense when they become cooler than their boiling point, and the liquid hydrocarbons then collect in trays and drain out.
- The long chain hydrocarbons condense at the bottom of the fractionating column because they
have high boiling points. - Meanwhile the shorter chain hydrocarbons condense at the top of the column because they have much lower boiling points.
When separating crude oil we use a fractionating column.
Is the top of the column hotter or cooler than the bottom?
Cooler
Cracking is the process in which …
Long chain hydrocarbons are split into smaller, more useful hydrocarbons.
Describe Catalytic cracking
- First, some long chain alkanes are heated until they vaporise into a gas
- Then they’re passed over a hot, powdered aluminium oxide catalyst
- This breaks the long chain alkanes into a shorter chain alkane and an alkene
How is steam cracking different to catalytic cracking?
Steam cracking is different because there is no catalyst involved. Instead the vaporised long chain alkane is mixed with steam at very high temperatures.
The difference between alkenes and alkanes is …
that alkenes have a double bond between two atoms, whereas alkanes only have single bonds
Another way to express the presence of the double bond between two carbon atoms is to say that alkenes are …
Unsaturated
Test for alkenes
The test to distinguish between alkanes and alkenes is the bromine water test.
Bromine water (just bromine dissolved in water) by itself is an orange colour. But when it’s mixed with alkenes, all of the bromine will react, and so the solution loses its orange colour, and turns colourless.
This doesn’t happen when bromine water is mixed with alkanes, because alkanes are not reactive enough to react with bromine water. So when mixed with an alkane, the solution will stay orange.
What type of reaction can an alkene be part of, because of the carbon to carbon double bond?
Addition reactions
An addition reaction between an alkene and water will produce an alcohol.
Once produced, the alcohol will dissolve in the water.
What process can be used to separate the alcohol from the water?
Fractional distillation
The alkene, ethene, reacts with water (vapour) to produce what?
Ethanol
General formula of alkenes
CnH2n
An alkene reacts with hydrogen to produce what?
An alkane
Which compound is produced in the following reaction?
C3H6 + H2 ➔ ?
Propane C3H8
Uses of poly(ethene)
Plastic bags
Bottles
Cling film
Uses of poly(chloroethene) - PVC
Window frames
Gutters / Pipes
Uses of poly(phenylethene) - Polystyrene
Takeaway cups
Packaging
Knives / forks
