C6.2 Flashcards
What are alkanes
- saturated hydrocarbons (joined by single covalent bonds only)
- unreactive
- made from alkenes + hydrogen
Formula for alkanes
CnH2n+2
What is a homologous series
Same general formula with each successive member differing with CH2
All have same chemical properties
How do alkanes react with air
Combust -
Complete = carbon dioxide and water
Incomplete = carbon monoxide and water
The larger the alkane molecule…
The stronger the intermolecular forces - the higher the boiling point
Crude oil temp gradient
Hot at the bottom + cold at the top
Highest boiling point
Eg, bitumen - will leave at the bottom of the fractionating column
Lowest boiling point…
Will leave the top as gas
What does cracking convert
Large alkanes into smaller alkanes and alkenes
What does cracking involve
Heating oil fractions to a high temperature (600-700) and passing over a hot catalyst of alumina or silica
- these break the covalent bonds
Why are large alkane molecules not useful
High boiling points - do not flow easily - very viscous - difficult to ignite can not be sold as fuels
As the alkanes increases in size
More viscous + higher boiling point
What are alkenes
- unsaturated hydrocarbons (at least 1 carbon to carbon double bond)
Formula for alkenes
CnH2n
Why do alkenes undergo addition reactions
Because of their double bonds
How to tests for presence of an alkene
- add bromine to an alkene to form dibrimo(alkene)
- orange-brown to colourless
Thermosetting polymers
- strong covalent bonds between layers
- can’t be reshaped easily
Thermosoftening polymers
Can be reshaped when heated
Easily separated
Can move over each other
Drawing addition polymers
Repeat units only have 2 carbons in central chain
What fictional group does alcohol have
Hydroxyl group - OH
General formula for alcohol
CnH2n+1OH
What happens when you oxidise an alcohol
Becomes a carboxylic acid
Alcohol + oxidising agent -> aloholoicacid + water
Oxidising agents for alcohols
Sodium dichromate - bright orange to dark green
Potassium manganate - purple to colourless
Functional group of carboxylic acid
Carboxyl group - COOH
Writing formula of acid
Ethanoic acid = CH3COOH
propanoic acid = CH3CH2COOH
(Each successive member differed by CH2)
If you react a carboxylic acid with a base
Salt + water
Carboxylic acid + metal carbonate
Salt water carbon dioxide
Carboxylic acid and metal
Salt and hydrogen
What is an ester
Made by reacting alcohols with carboxylic acids in the presence of a sulphuric acid catalyst x other product is water
What are polyesters
Formed when both an alcohol and carboxylic acid have two functional groups
Diol +. Dicarboxylic acid
- two water molecules forming 2n-1
