1 of 1

Alkenes

Hydrocarbons with a double carbon-carbon bond.

Unsaturated

Alkenes are unsaturated because they contain two fewer hydrogen atoms than their alkane counterparts.

General formula for alkenes

C_nH_2n

Functional group

Alkenes are hydrocarbons in the functional group C=C.

The functional group of an organic compound determined their reactions.

Alkene reactions

Alkenes react with oxygen in the same way as other hydrocarbons, just with a smoky flame due to incomplete combustion.

Alkenes also react with hydrogen, water and the halogens. The C=C bond allows for the addition of other atoms.

Functional group

-OH

​

For example: CH₃CH₂OH

Methanol, ethanol, propanol and butanol are the first four of the homologous series.

Alcohol reactions

Alcohols react with sodium, air and water.

Alcohols and sodium:

bubbling, hydrogen gas given off and salt formed.

​

Alcohols and air:

alcohols burn in air releasing carbon dioxide and water.

​

Alcohols and water:

alcohols dissolve in water to form a neutral solution.

Fermentation

Ethanol is produced from fermentation.

When sugar solutions are fermented using yeast, aqueous solutions of ethanol are produced. The conditions needed for this process include a moderate temperature (25 – 50⁰C), water (from sugar solution) and an absence of oxygen.

Functional group

-COOH

​

For example:

CH₃COOH

Methanoic acid, ethanoic acid, propanoic acid and butanoic acid are the first four of the homologous series.

Carboxylic acid reactions

Carboxylic acids react with carbonates, water and alcohols.

Carboxylic acids and carbonates:

These acids are neutralised by carbonates

Carboxylic acids and water:

These acids dissolve in water.

Carboxylic acids and alcohols:

The acids react with alcohols to form esters.

Strength (HT only)

Carboxylic acids are weak acids

Carboxylic acids only partially ionise in water.

An aqueous solution of a weak acid with have a high pH (but still below 7).

Polymers

Alkenes are used to make polymers by addition polymerisation.

Many small molecules join together to form polymers (very large molecules).

Displaying polymers

In addition polymers, the repeating unit has the same atoms as the monomer.

It can be displayed like this:

​

​

​

​

Condensation polymerisation

Condensation polymerisation involves monomers with two functional groups

When these types of monomers react they join together and usually lose small molecules, such as water. This is why they are called condensation reactions.

DNA

Deoxyribonucleic acid is a large molecule essential for life. DNA gives the genetic instructions to ensure development and functioning of living organisms and viruses.

DNA structure

Most DNA molecules are two polymer chains made from four different monomers, called nucleotides. They are in the double helix formation.

Natural polymers

Other naturally occurring polymers include proteins, starch and cellulose and are all important for life.