C7 - Organic chemistry

Hydrocarbons:

Hydrocarbons only contain hydrogen and carbon atoms

Hydrocarbons form homologous groups, these consist of Alkanes, Alkenes, Alcohols and carboxyl group.

Hydrocarbon properties change as they increase in length. 1. As the length of the hydrocarbon increases, it becomes more viscous

  1. The shorter the chain the more volatile the hydrocarbon is, this means that is will turn into a gas at a lower temperature. So the shorter the hydrocarbon chain, the lower the temperature at which that hydrocarbon vapourises and condenses.
  2. The shorter the carbon chain the more flammable the hydrocarbon is.

Alkanes:

Alkanes are a form of hydrocarbon

General Formula: C2H2N+2

The alkanes are a homologous series, a group of hydrocarbons that react in the same way.

The first 4 most common alkanes are: Methane, Ethane, Propane and Butane.

Alkanes are saturated compounds: Each carbon atom forms 4 single bonds.

Complete combustion of hydrocarbons:

Hydrocarbon + Oxygen = Carbon Dioxide + Water + (Energy)

Hydrocarbon complete combustion only has water and carbon dioxide as products. During the reaction, both Oxygen and Hydrogen are both oxidised.

Fractional Distillation:

Crude oil is formed over millions of years, it is made up of dead organisms, mainly plankton, and over millions of years, the high temperature and pressure have caused it to turn to crude oil.

Crude oil is a non-renewable source of fuel and energy, it is finite. This means it will run out.

Crude oil is made up of many different hydrocarbons, the majority are alkanes. The different compounds can be separated by fractional distillation.

In the fractional distillation column, the crude oil is heated in order to separate the different. This occurs due to the different evaporation points of the fractions of crude oil. The different hydrocarbons are called fractions.

Uses and cracking of crude oil:

Crude oil provides fuel for transport, This includes fractions of crude oil such as petroleum and Diesel. The petrochemical industry uses some fractions of cure oil to create other chemical compounds such as polymers, solvents and lubricants.
All products from Crude OIl are organic compounds, the variety of compounds found is due to carbons ability to bond in many different ways and create different groups called Homologous groups.

Cracking means splitting long-chain hydrocarbons.

Short chain hydrocarbons are highly flammable so are very good fuels and are in high demand. However longer chain hydrocarbons are not in such demand as they form more viscous substances such as Tar. This can be solved as cracking can split larger hydrocarbon chains into smaller ones, this allows more useful products to be created. This is called cracking.
Cracking produces two types of hydrocarbon, these are alkenes and alkanes.

Methods of cracking:

Cracking is a form of thermal decomposition.

The first step is to heat long-chain hydrocarbons to vaporize them. The vapour can then be passed over a hot powdered aluminium catalyst. The long chain molecules split apart on the surface of the catalyst. This is called catalytic cracking.

Alkenes and their reactions:

Addition polymers:

Alcohols:

Carboxylic Acids:

Alkenes have a c = c bond, this means they have 2 fewer hydrogen bonds than alkanes. The c= c bond allows they alkene to be highly reactive as it can separate and allow 2 bonds to be created.

General formula: CnH2n

First four alkenes are Ethene, propene, butene and pentene. For pentene and pentene the c=c bond can occur in different places.

Alkenes burn with a smoky flame, this is because the combustion is incomplete so carbon monoxide is produced along with co2 and water. Alkenes react in addition reactions, the c=c bond opens up to allow reaction with 2 bonds created. Addition of hydrogen is known as hydrogenation

Halogens react with alkenes to satuarte the alkene. Example: Dibromoethane

Bromine water test: When bromine water is added to a saturated compound no colour change will occur. If added to an alkene, which is unsaturated, the colour will change from orange to colourless.

Polymers are made up of lots of the same molecule joined together in a long chain. Polymers are formed from the addition of smaller molecules called monomers. This reaction is called polymerisation. Monomers are often alkenes.

Alchohols have an -OH functional group and end in "ol"

Monomers have a c=c bond, this broken to allow the addition of 2 new bonds either side of the molecule in the straight chain polymer. Monomers must be unsaturated to allow polymerisation to occur.

Polymerisation representations can be reversed and unsaturated to find the monomer that reacted with the polymer.

Functional group -COOH. Homologous series all containing the -COOH. Names end in anoic acid. This is used in conjunction with the 4 alkane/kene names

General formula: CnH2n+1OH. First 4 alcohols are methanol, ethanol, propanol, butanol.

The first four alcohols have similar properties: Alcohols are flammable and undergo complete combustion in air. The first 4 are all soluble in water and have a neutral PH. React with sodium - product hydrogen. Alcohols can be oxidised to produce carboxylic acids. Alcohols are used as solvents and the first 4 are used as fuels.

Ethanol can be produced by fermentation of yeast - Fermenter can be used to ferment yeast and sugar into ethanol, fermentation occurs best at 37 degrees and with a slight acidity.

Carboxylic acids react in the same way as other acids. When they react the create an "anoate". For example methanoic acid in methanoate.

Carboxylic acids can dissolve in water, when they do so they release h+ ions into the water. Weaker acidic solutions have a higher ph than stronger acids when ionising.

Esters: Made from carboxylic acids. Esters have the functional group -COO-. Esters are formed from an alcohol and a carboxylic acid. A catalyst is usually used. (Acidic catalyst). Ester = alcohol + carboxylic acids = ester + water. Must learn the ester ("Ethyl Ethanoate").

Condensation polymerisation

Condensation polymerisation involves monomers which contain different functional groups. Monomers react together and form bonds that create a polymer chain. For each new bond formed, a small molecule is lost, that is why it is called condensation polymerisation.

Condensation polymerisation: two monomer types each containing two of the same functional group. or one monomer type with two different functional groups. Two types of product - The polymer and the small molecule.
Two reactive groups on each monomer.

Naturally occurring polymers

Amino acids have an amino group and a carboxyl group. Basic amnio group formula: NH2. Carboxyl group - COOH

Proteins are polymers of amino acids - Amino acids can form long chain polymers called polypeptides via condensation polymerisation. Proteins are made up of long chain polypeptides, they act as biological catalysts in the body when used in reactions with enzymes.

DNA molecules - Made from nucleotide polymers. Deoxyribonucleic acid contains genetic information that is replicated and allows development. It is a large molecule that takes a double helix structure. DNA is made from two smaller polymer chains called nucleotides. Each contains a base, initials A, C, G, T. The bases combine and create cross-links creating the double helix structure.

Sugars - Small molecules that contain carbon, oxygen and hydrogen. Sugars can react through polymerisation to form larger polymers. E.g. Starch and Cellulose.