C7 - Organic Chemistry
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What is the formula for an alkane?
C n H 2 n+2
What does ‘saturated’ mean for alkanes?
It consists of only single bonds. C-C.
Describe a homologous series.
Organic compounds that react in a similar way.
Name the first 4 alkanes.
• Methane • Ethane • Propane • Butane
Why does viscosity change for each hydrocarbon?
The shorter it is, the less viscous (gloopy) it is.
What length hydrocarbons are more volatile?
Shorter hydrocarbons are more volatile.
Why does the flammability change for each hydrocarbon?
The shorter it is, the more flammable (easy to ignite) it is.
When will complete combustion happen?
When there is enough oxygen
Give the word equation for incomplete combustion.
hydrocarbon + oxygen → carbon dioxide + water (+ energy)
What happens to hydrocarbons during complete combustion?
They oxidise.
Why are hydrocarbons useful as fuels?
Because of the amount of energy they produce during complete combustion.
How was crude oil formed?
Dead plants and animals (mainly plankton) became trapped in mud under a high temperature and pressure.
Give 1 problem with Crude Oil.
It is a finite resource, non-renewable.
What is crude oil?
A mixture of lots of different hydrocarbons.
What is the first step of Fractional Distillation?
Crude oil is heated to around 450 degrees so it vaporises.
What happens in fractional distillation after crude oil has been heated?
The gas enters a fractionating column, where there is a temperature gradient.
How does the crude oil separate once in a column?
Long hydrocarbons have a high boiling point so cool and condense into liquids near the bottom of the column. Opposite for short hydrocarbons.
Give 2 uses of crude oil.
• Fuel 2. Petrochemical industry (e.g. for polymers, solvents, lubricants)
What is the goal of fractional distillation?
To separate crude oil into fractions.
What is the goal of cracking?
To produce shorter, more useful alkanes and alkenes from longer hydrocarbons.
How do you test for alkenes?
Put in bromine water and shake. If the orange bromine water becomes decolourised, an alkene is present.
What type of reaction is cracking?
Thermal decomposition.
Describe catalytic cracking in 3 steps.
• Vaporise • Pass over hot powdered aluminium oxide catalyst. • Long-chain splits on surface of specks of catalyst.
Describe steam cracking in 3 steps.
• Vaporise • Mix with steam • Heat to a higher temp