Organic Chemistry | AQA GCSE Chemistry Notes | Topic 7

• Hydrocarbons are compound containing hydrogen and carbon atoms only.
• Crude oil is a mixture of hydrocarbons. It is found in rocks.
• Fractional distillation is used to separate the long and short hydrocarbons in crude oil.
• Vaporise the crude oil. Insert into the column. The column is hot at the bottom and cold at the top. The long hydrocarbons are stronger so they can condense at the bottom of the column, and leave. The shorter ones rise, and then leave when they pass their boiling point.
• Short hydrocarbons have a lower mp/ bp. They are more flammable, more volatile, less viscous. They are more useful as fuels.
• Cracking is used to shorten long chain hydrocarbons.
• Steam cracking uses steam, catalytic cracking uses 600*C and an aluminium oxide catalyst.
• Monkeys eat peanut butter.
• The alkanes are methane, ethane, propane and butane. C_nH_2n+2.
• Complete combustion: X + O₂ --> CO₂ + H₂O.
• Test for alkenes: react with bromine water, they turn orange to colourless.

Triple Science Students Only

• The alkenes are ethene, propene and butene. C_nH_2n.
• When drawing alkenes, check that each Carbon has 4 bonds, so remove any extra hydrogens.

• Alkenes are more reactive than alkanes, due to the double bond being able to open up.
• Test for alkenes: react with bromine water, they turn orange to colourless.
• Combustion: alkenes and alkanes also react with oxygen.
• Complete combustion: X + O₂ --> CO₂ + H₂O.
• Incomplete combustion: X + O₂ --> CO + H₂O.
• Carbon monoxide (CO) is poisonous.
• Alkenes burn with smoky flames because of incomplete combustion.
• Alkenes react with hydrogen, water and halogens to form alkanes and alcohols.
• Alkenes also produce addition polymers (formed when the double bond opens up, and many monomers join together).
• Alcohol functional group: -OH.
• First four alcohols: methanol, ethanol, propanol and butanol.

• Ethanol: produced when sugar solutions are fermented using yeast.
• Conditions:
• Carboxylic acids functional group: –COOH.

• First four carboxylic acidds: methanoic acid, ethanoic acid, propanoic acid and butanoic acid.
• Carboxylic acids react with carbonates, dissolve in water, react with alcohols.
• Carboxylic acids are weak acids because they only partially ionise in solution.
• Carboxylic acids react with water to produce acidic solutions.
• Carboxylic acids react with carbonates in the same way as acid + metal carbonate forming salt, water, carbon dioxide (topic 4)
• Carboxylic acid + water (with acid catalyst) forms an ester.
• The only ester we need to know is ethyl ethanoate.
• It is made up of ethanol and ethanoic acid, by removing water then combining.
• Polymer: long chain molecule by joining many monomers.
• Monomer: used to make a polymer
• Repeat unit: cirlce the part of the polymer that repeats.
• Addition Polymer: break the double bond from alkenes and join
• Condensation Polymer: remove the H₂O from the middle and join carboxylic acids or alcohols to each other.
• Amino acids have two different functional groups in a molecule.
• Amino acids react by condensation polymerisation to produce polypeptides. e.g. glycine is H₂NCH₂COOH and polymerises to produce the polypeptide
• Different amino acids can be combined in the same chain to produce proteins.
• DNA (deoxyribonucleic acid) is a large molecule essential for life.
• DNA encodes genetic instructions for the development and functioning of living organisms and viruses.
• Most DNA molecules are two polymer chains, made from four different monomers called nucleotides, in the form of a double helix.
• Other naturally occurring polymers important for life include proteins, starch and cellulose.