Topic 7; Organic Chemistry Flashcards
What is crude oil?
Mixture of compounds; consists of the remains of ancient fossilised biomass
Finite resource
What is a hydrocarbon?
A compound made up of just hydrogen and carbon
What are alkanes?
Saturated hydrocarbons with formula CnH2n+2
What is a homologous series?
Series of compounds with same general formula, function groups and proprerties
Describe combustion of hydrocarbons
- exothermic reaction; hydrocarbons react with oxygen
- complete combustion; carbon dioxide and water (hydrocarbon completely oxidised)
- incomplete combustion produces water and carbon monoxide
Describe the physical properties of alkanes
Boiling points and viscosity increase as molecule size increases
Volatility and flammability decrease as molecule size increases
Poor reactivity
What is cracking?
Large hydrocarbons thermally broken down into smaller and more useful molecules
What type of reaction is cracking?
Thermal decomposition
What are 2 conditions needed for cracking
- Heated to vapour and passed over hot catalyst
2. Heated to vapour, mixed with steam and heated to high temp
How are the products of cracking used?
Alkanes and alkenes- used as polymers
What is an alkene?
Unsaturated hydrocarbon. Contains C=C bond. CnH2n
What is the test for alkenes?
Add bromine water; colour change occurs from orange to colourless
Describe the combustion of alkenes.
Theyburn with smokey flames due to incomplete combustion
How does fractional distillation of crude oil takes place?
- crude oil heated and vaporised
- vapour rises up fractioning column
- column hotter at bottom and cooler at top
- hydrocarbons cool as they go up and condense at different heights (different boiling points)
- large molecules, high boiling points, at bottom
- small molecules, low boiling points, at top
- gives fractions-used in various ways
