Topic 7 Organic Chemistry Flashcards
What is crude oil?
Crude oil is a mixture of compounds: a fossil fuel consisting of the remains of ancient biomass.
It is also a finite source of energy.
What is a hydrocarbon?
A compound made up of exclusively carbon and hydrogen atoms.
What are alkanes?
Saturated hydrocarbons of the general formula CnH2n+2.
What is a homologous series?
A series of compounds with the same general formula and similar chemical properties.
Describe the combustion of Hydrocarbons
- Exothermic reaction when hydrocarbons are reacted with oxygen
- Complete combustion creates carbon dioxide and water (carbon and hydrogen atoms are completely oxidised)
- Incomplete combustion creates carbon or carbon monoxide and water
Describe the physical properties of alkanes
- The first few in the series are gases, and then change to liquids and then to solids
- In general, the boiling points and viscosity increase as the molecules get bigger
- Volatility and flammability decrease as the molecules get bigger
- Poor reactivity
Explain how fractional distillation of crude oil takes place
- Crude oil is heated and vapourised
- Vapour rises up the fractioning column
- The column is hotter at the bottom and cooler at the top
- Hydrocarbons cool as they go up the column and condense at different heights, as they have different boiling points
- Large molecules with high boiling points are collected at the bottom
- Smaller molecules with lower boiling points are collected at the top
What is cracking?
When large hydrocarbons are thermally broken down into smaller more useful molecules.
What type of reaction is cracking?
Thermal decomposition
What are the conditions needed for cracking?
Reactants are heated to a vapour and passed over a hot catalyst (catalytic cracking) or mixed with steam and heated to high temperatures (steam cracking).
How are the products of cracking used?
The products are alkanes and alkenes - used as polymers and starting materials for synthesis
What is an alkene?
An unsaturated hydrocarbon that contains a C=C bond. Has the general formula CnH2n
What is the test for an alkene?
Add bromine water = a positive result is a colour change from orange to colourless
Describe the combustion of alkenes
They burn with a smoky flame due to incomplete combustion
Describe the addition reactions for alkenes
The reaction is an ‘addition’ reaction because one molecule combines with another molecule, forming one larger molecule and no other products (the double bond is reduced to a single bond)
- With hydrogen (hydrogenation) requires a higher temperature and a nickel catalyst
- With steam (hydration) requires a high pressure and temperature and concentrated phosphoric acid catalyst
- With the addition of halogens
