Chemistry AQA AS Unit 1 Alkanes

Made these notes for my year 12 summer exam to revise and read over. There are spelling mistakes in most of my files but due to the busy exam schedule I had no time to correct them (sorry).

Most files have more information than what is needed but I feel it helps you feel more confident walking into the exam if you have a greater knowledge background and may help when having to apply knowledge to questions. Good luck :)

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  • Created by: Chelcie
  • Created on: 02-09-13 12:59
Preview of Chemistry AQA AS Unit 1 Alkanes

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Alkanes
General formula:
CnH2n+2
Unbranched, branched or ringed.
Polarity:
Almost non-polar because of similar electronegativities.
Weak V.D.W. forces.
Boiling points:
As the chain length increases, the boiling point increases due to the number of V.D.W. forces
increasing.
Alkanes with branched chains cannot pack as closely as unbranched chains, so melting points are
lower as V.D.W forces are not as effective.
Solubility:
Insoluble in water as the hydrogen bonds are stronger than the V.D.W.
How alkanes react:
Unreative normally. They have strong carbon-carbon/carbon-hydrogen bonds. They do burn and will
react with halogens under suitable conditions.
Fractional Distillation of Crude Oil
Crude oil is mostly a mixture of branched and unbranched alkanes.
It is done in a fractionating tower.
1. Crude oil heated in a furnace.
2. The mix of liquid and vapour passed into a tower cooler at
the top than at the bottom.
3. Vapour passes up the tower (via a series of trays containing
bubble caps) until they arrive at a tray lower than their
boiling point. They condense and are then piped off.
4. The thick residue at the bottom is tar/bitumen. It is often
processed again to provide more valuable products.
The shorter the hydrocarbon chain, the nearer the top they
condense because they have the lowest boiling points.

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Industrial Cracking
Shorter chain products are more economically valuable due to supply not meeting demand.
Thermal cracking...
700K-1200K
High pressure 7000kPa
Free radicals are formed due to one electron in a paired covalent bond goes to each carbon chain in
the break.
The free radicals are highly reactive intermediates.
Alkenes are not cracked for long to avoid decomposition.
Catalytic cracking...
Lower temperature- 720K
Lower pressure (but more than atmospheric)
ZEOLITE CATALYST... Silicon dioxide and Aluminium oxide
Zeolites have a honeycomb structure with large surface area.…read more

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Exacerbate asthma, cause cancer.
Unburnt Hydrocarbons
Greenhouse gases, photochemical smog.
Carbon dioxide
Greenhouse gas.
Produced when hydrocarbons are burned.
Water vapour
Greenhouse gas
To remove sulfur... FLUE GAS DESULFURISATION
Some chimneys use CaO, CaCO which produces gypsum CaSO (plaster)
Catalytic convertors...
Honeycomb made of ceramic material, coated with rhodium and platinum metals.
Large surface area.…read more

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