Organic chemistry 7 Flashcards
What is crude oil?
Crude oil is a mixture of compounds; a fossil fuel consisting of the remains of ancient biomass
Finite resource - cannot be replaced as it is used up
What is a hydrocarbon?
A compound made up exclusively of hydrogen and carbon atoms
What are alkanes?
Saturated hydrocarbons of a general formula CnH2n+2
What is homologous series?
Series of compounds with same general formula, same functional groups and similar chemical properties
Describe the combustion of hydrocarbons
- Exothermic reaction occurring when hydrocarbons are reacted with oxygen
- Complete combustion produces carbon dioxide and water (carbon and hydrogen atoms are completely oxidized)
- Incomplete combustion produces carbon or carbon monoxide and water
Describe the physical properties of alkanes
- First few in series are gases, then change to liquids, then to solids
- In general, boiling points and viscosity increase as molecules get bigger
- Volatility and flammability decrease as molecules get bigger
- Poor reactivity
Explain how fractional distillation of crude oil takes place
- Crude oil is heated and vaporized
- Vapor rises up the fractionating column (tower)
- 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, high boiling points - collected at the bottom
- Small molecules, low boiling points - collected at the top
- This gives fractions, which can be used in various way
What is cracking?
When large hydrocarbons are thermally broken down into smaller and useful molecules
What type of reaction is cracking?
Thermal decomposition
What are the conditions for cracking?
Reactant heated to vapor, passed over a hot catalyst (catalytic cracking) or heated to vapor, 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?
Unsaturated hydrocarbon. Contains a C=C bond
General formula for alkenes is CnH2n
What is the test for alkenes?
Add bromine water. Colour change occurs from orange to colourless
Describe the combustion of alkenes
They burn with smoky flames due to incomplete combustion
Describe addition reactions of alkenes
Addition atoms across the carbon-carbon double bond so that the double bond becomes a single carbon-carbon bond.
a) With hydrogen - hydrogenation; requires a higher temperature and a nickel catalyst
b) With steam - hydration; requires high temperature, pressure, and concentrated phosphoric acid (H3PO4) as a catalyst
c) With Br2/Cl2/I2 - addition of halogens
