Unit 7-Organic chemistry

• What is a hydrocarbon?


  A compound that’s formed/made up of carbon and hydrogen atoms only
• Explain alkanes


  They are saturated compounds, where each carbon atom forms 4 single covalent bonds

  they are a homologous series
• What’s a homologous series? 


  A group of organic compounds that react in similar ways/a group of compounds with the same general formula
• What’s the general formula of alkanes?

  CnH2n +2
• What are the first four alkanes?


  Methane(CH4-the formula)

  Ethane

  Propane

  butane
• What are the properties of the shorter carbon chains/smaller alkanes?


  More runny/less viscous

  more volatile/lower boiling points

  more flammable/easier to ignite

  clean flame

  flows easily
• What are the properties of longer/large alkanes?


  High boiling points(it’s harder to break the large/strong intermolecular forces between the bonds)

  Hard to ignite/catch fire

  Smoky flame

  Doesn’t flow easily

  more viscous
• what is complete combustion?


  Burning which needs O2 from the air, but this is when O2 isn’t the limiting factor anymore as there’s a good supply of air and oxygen
• Explain complete combustion of a hydrocarbon fuel

  Carbon and hydrogen atoms in the fuel react with O2 in an exothermic reaction

  CO2 and water are produced

  The maximum amount of energy is given out/it releases lots of energy

  hydrocarbons are used as fuels due to the amount of energy released when they combust completely

  during combustion, the carbon and hydrogen from hydrocarbon are oxidised
• What’s the equation for hydrocarbon plus oxygen during complete combustion? And given an example using methane.

  hydrocarbon + oxygen—> carbon dioxide + water

  Methane + oxygen—> carbon dioxide + water
• What is incomplete combustion?


  Burning when the supply of air or O2 is poor

  water is still produced, but carbon monoxide and carbon are produced

  less energy is released and in complete combustion
• What is/explain the process of crude oil?

  It’s unprocessed oil which is taken directly from the ground, either land or sea and is a fossil fuel/non-renewable

  it’s a hydrocarbon

  It’s formed from the remains of plans and animals, mainly plankton, that died millions of years ago and was buried in mud

  over millions of years ,with high temperature and pressure ,the remains turn into crude oil which can be drilled up from rocks where it’s found
• Why do we use fractional distillation for crude oil?

  As crude oil isn’t useful in its original state, as it’s made up of different hydrocarbons that need to be separated

  it gets separated into the different compounds by fractional distillation
• Explain the process of fractional distillation of crude oil

  The oil is heated until most has turned into a gas, and the gas is enter a fractionating column

  In the column, there’s a temperature gradient(hot at the bottom ,gets cooler higher up ,which separates different compounds with different boiling points)

  The longer/large hydrocarbon molecules have high boiling points, which condensed back into liquids and drain out of the column early on/lower down

  The smaller/shorter hydrocarbons have lower boiling points, so evaporate and condense much later, near top of column where it’s cooler
• What do you end up with after fractional distillation of crude oil?

  You end up with the crude oil mixture separated into different fractions, and each one has a mixture of hydrocarbons that have a similar number of carbon atoms, so they have similar boiling points
• Why are the fractions of crude oil mixtures?


  As the fraction boils over a range of temps rather than one specific temp
• List the six products that have been separated due to the fractional distillation of crude oil

  1-liquefied petroleum gas

  2-gas

  3-kerosene

  4-diesel oil

  5-heavy fuel oil

  6-bitumen
• What are the uses of crude oil?


  Provides fuel for transport

  as a feed stock to make new compounds for use in things like polymers
• What are alkanes and alkenes both examples of?

  The homologous series
• why is cracking used for hydrocarbons?

  Short chain hydrocarbon molecules are flammable so they make good fuels with high demand, where as long chain hydrocarbons form thick gloopy liquids like tar which aren’t useful

  therefore, a lot of the longer alkane molecules produced from fractional distillation are turned into smaller, more useful ones by cracking
• What is cracking?

  A thermal decomposition reaction which breaks down molecules by heating them
• As well as alkanes, what type of hydrocarbon does cracking Produce

  Alkenes
• Describe Alkenes


  They are a lot more reactive than alkanes

  Used as a starting material when making other compounds and can be used to make polymers. They’re unsaturated hydrocarbons

  Can be tested with bromine water
• Why are alkenes very reactive and what happens to them


  Due to the double carbon bond which undergoes addition reactions, when the double carbon bond becomes a single carbon bond, and other atoms join onto the two carbon atoms
• How can you test for Alkenes and explain it


  Through bromine water

  Alkenes decolourise/ react in bromine water

  When it’s added to an alkene, it reacts to make a colourless compound, so the bromine water is decolourise

  (when orange bromine water is added to an alkane, no reaction happens and it stays orange)
• Explain the 2 cracking processes of hydrocarbons

  Heat the long chain hydrocarbons to vaporise them

  then the Vapour is passed over a powered aluminium oxide catalyst

  The molecule split apart on the surface of the specs of the catalyst, which is called catalyst cracking

  or you can crack hydrocarbons if you vaporise them, mix them with steam, then heat them to a high temperature, which is called steam cracking
• What do you do to convert alkane structure diagrams into alkene structure diagrams/alkanes into alkenes


  You add the double bond of an alkene, and take away two hydrogens
• What is the alkenes general formula

  CnH2n
• How do you turn Alkenes into alkanes?/with a diagram.


  You take away the alkenes double bond, and add the 2 new atoms to the extra spaces
• How do you balance chemical equations for cracking?

  Turn the long chain hydrocarbon molecule(as there’s too much of it in crude oil) into a shorter alkane molecule + an alkene