Chemistry - Organic Chemistry

Contain only Hydrogen and Carbon atoms, like Alkanes

Alkanes

• Their formula is Cn+H2n+2.
• They are homologous (a group of compounds reacting in a similar way).
• They are saturated (each carbon forms 4 single covalent bonds)
• The first four are Methane, Ethane, Propane and Butane
• The shorter the chain, the less viscous, the lower the boiling point but the more flammable
• The combustion of any hydrocarbon in oxygen releases alot of energy, as well as CO2 and water. Hydrocarbons are often used as fuel
• In combustion both C and H from hydrocarbons are oxidised (with oxygen)

          Crude Oil

• Fossil fuel formed from the remains of plankton
• It is a mix of multiple hydrocarbons (mainly alkanes)
• They can be seperated through Fractional Distilation

1. The oil is heated untill most of it is a gas, the gas enters a fractioning column, and liquid is drained. In the column, the temperature decreases further up. 

2. The longer chains have higher boiling points, so condense back into liquids and drain off earlier on.

3. The shorter chains have lower boiling points so condense back into liquids  and drain off much later on, near the top where it is cooler.

Short-chain hydrocarbons are flammable so are used for fuel, while long-chain hyfrocarbons form thick/gloopy liquids that aren't useful. So they are put through cracking, which produces alkanes and alkenes. Alkenes are starting materials - it is used to make other compounds and polymers. Some of the products are used as fuel.

Cracking is a thermal decomposition reaction, breaking molecules down by heating them up.

• 1) Long chains are heated untill they turn to a gas (vaporise)
• 2) The vapour is passed over hot powdered aluminium oxide catalyst
• 3) Long-chain molecules split apart on the surface of the catalysts (catalytic cracking)

This can also be done by mixing the vapour with steam then heat them up to a very high temperature (steam cracking)

An alkene are made up very similarly to alkanes, but two of the carbons in the chain have a double bond with each other rather than with another hydrogen. (One hydrogen rather than two)

The fact that alkenes have a C=C bond, they have two less hydrogens, making them unsaturated. However the double carbon bond can be opened up so that the carbons ond with other atoms in a single bond, making them far more reactive than alkanes. The first alkene is ethene (two carbons), then propene, butene and pentene. The formula is CnH2n. The double carbon bond can be anywhere in the chain.

With large amounts of oxygen, alkenes combust completely to produce just water and CO2, but when alkenes are burnt in the air they undergo incomplete combustion producing water, CO2 and carbon, carbon monoxide (poisonous). This results in a smoky flame and less energy being released.

A functional group is a group of atoms in a molecule that determines how that molecule reacts. Alkenes have C=C so react similarly, so you can work out the products of their reaction.

Alkenes often react in addition reactions where the C=C opens up and another atom is added to each. Adding hydrogen is hydrogenation, this makes it the equilvalent alkane (it uses a catalyst)

Alkenes also react with halogens (bromine, chlorine, iodine) e.g. ethene and bromine make diobromoethane. This specific reaction can e used to test of alkenes: orange bromine water is added to a saturated compound like an alkane, nothing happens. But when added to an alkene, it will become colourless.

When steam is added to an alkene, it makes and alcohol. One of the carbons opens to bond to a hydrogen, and the other bonds with and OH, ethene + water = ethanol. This is done industrially. After ethanol has been made in a factory, it is put in a condenser, where water and ethanol have a higher boiling point than the ethene, so they are collected while the ethene is recycled. The ethanol is purified by fractional distillation.

Plastics are made of long chains called polymers which are formed from small monomers joined together (polymerisation) with high pressures and a catalyst. The monomers in plastics are usually alkenes.

Addition polymers are made from unsaturated monomers, that have double covalent bonds (e.g. alkenes). Many unsaturated monomers can open up their double bonds and bond with eachother. There is only one product, so it has the same number of atoms as the monomers that formed it.

The functional group of alcohols are OH and the general formula is CnH2n+1OH

Alcohols are formed the same as alkanes, but instead of a carbon reacting with hydrogen at the end, it reacts with an O-H  The first four alcohols are Methanol, Ethanol, Propanol and Butanol, that have similar properties

Alcohols are flammable so undergo complete combustion in air. The first four are soluble in water and have a neutral pH and react with sodium, producing hydrogen amongst others.

Alcohols can be oxidised (with oxygen) to make carboxylic acid, where the last carbon has a souble bond with oxygen and a single bond with OH rather than just OH. E.g. ethanoic acid

Alcohols like methanol and ethanol can be used in the solvents industry as they are able to disolve things that water can't. The first 4 can be used as fuel.

Ethanol is usually made through fermentation, where an enzyme in yeast converts sugars into ethanol (and CO2). The ideal conditions are at 37C, in a slightly acidic solution but in anaerobic conditions

They have the functional group -COOH and the meth/eth/prop/but end in anoic. The have the same structure as the hydrocarbons, but the last carbon, instead of bonding with hydrogen, double bonds with and oxygen, and single bonds with an OH.

Like other acids, they react with carbonates to make a salt, water and CO2, where the salt ends with -anoate e.g. sodium ethanoate. Carboxylic acids don't fully ionise in water, forming weak acidic solutions. Making them less acidic and have a higher pH than aqueous solutions of strong acids of the same concentrations.

Carboxilic acids can react with alcohols (using an acidic catalyst) to make esters (and water) which have the functional group -COO-. E.g. Ethanioc acid + ethanol = Ethyl Ethanoate

Involves monomers that contain different functional groups. These monomers react together and form bonds to make polymer chains. But for each new bond that forms, a small molecule is lost (hense condensation). The simplest ones contain only two types of monomers.

E.g. A diol (ethane diol (carbon chain with OH on either end)) + a dicarboxylic acid (carboxylic acid with the OH-C=O on either side) = a condensation polymer (polyester) + 2nH2O

Amino Acids

Amino acids contain two functional groups, a basic aamino group (NH2) and an acidic carboxyl group (COOH) on either side of a C with two single H bonds. The most simple is glycine

Proteins

Amino acids from polymers known as polypeptieds via condensation poly. where the amino group of the acid reacts with the acid group of another and so on. With each bond a molecule of water is lost. One or more of these polymers are proteins (enzymes, haemoglobing, antibodies, body tissue).

DNA

Made of two polymer chains of monomers called nucleotides. containing bases.

Simple Sugars can form Polymers

Sugars can react togeter to form larger polymers (starch, cellulose)