Organic Chemistry Part 2 Flashcards
What is cracking?
Breaking down long-chain hydrocarbons into more useful short-chain hydrocarbons.
Thermal decomposition
How is cracking carried out?
Alkanes are vaporised and passed over a catalyst (silica or alumina) at 600-700°C. This produces short-chained alkanes, and alkenes.
What are allkenes?
Unsaturated hydrocarbons (carbon-carbon double covalent bond)
General formula for alkenes
CnH2n
Reactions of halogens with alkenes
Halogens react with alkenes to make haloalkanes
eg bromine + ethene -> dibromoethane
Addition reactions
Test to distinguish between alkanes and alkenes
Shake with orange bromine water
Alkanes: Solution stays orange
Alkenes: Solution becomes colourless (dibromoalkane produced)
Why is cracking necessary?
To meet the high demand for short-chain hydrocarbons, eg octane (used for petrol)
How is an addition polymer formed?
Joining up many small molecules called monomers.
What is a monomer?
A small molecule that joins up with many others to form a polymer.
What are the problems with the disposal of addition polymers?
They are not biodegradable as they are inert (due to very strong carbon-carbon bonds)
When burned, they produce toxic gases.
Formula of polytetrafluoroethene
(C2F4)n
Formula of polychloroethene
(C2H3Cl)n
Formula of polypropene
(C3H6)n
