Organic Chemistry Flashcards
Homologous Series
- Same general formula
- Differ by a CH\/2 unit
- Show gradual variation in physical properties
- Similar chemical properties
Hydrocarbons
- Containing only hydrogen and carbon
- Saturated bonds are joined by a single C-C bond
- Their ability to combust depends on the amount of oxygen available
Alkanes
- Saturated hydrocarbons
- General formula CnH2n+2
- No functional group
- Gas at room temp/pressure
Crude Oil/ Fractional Distillation
- Crude oil is made up of organisms that were buried in mud millions of years ago. It is a complex mixture of hydrocarbons. It is also used as feedstock, the main resource for the petrochemical industry.
- Each simpler mixture in crude oil is called a fraction. Crude oil is seperated into fractions because they have different purposes
- FRACTIONAL DISTILLATION:
1. Crude oil enters tall fractioning column, which is hotter at the bottom.
2. Vapours from the oil rise from the bottom.
3. Each fraction condenses when it becomes cool enough, each at a different point in the column.
4. Pipes lead each fraction away.
5. Small hydrocarbon molecules leave the top as refinery gases, long hydrocarbon molecules leave the bottom as bitumen
Uses of each alkane gas:
Refinery gases - Bottled gases
Petrol - Car fuel
Naphtha - Manufacture chemicals and plastics
Kerosene - Fuel for aircrafts
Diesel - Fuel for cars/trains
Fuel oils - Fuel for ships
Bitumen - To surface roads/roofs
Combustion
ALKANES:
- Complete combustion when plentiful oxygen supply, exothermic reaction. Carbon dioxde and water produced, max energy given out.
- Incomplete combustion when limited oxygen supply. Carbon, carbon monoxide and water are produced.
- Carbon monoxide is poisonous. Can stop oxygen from flowing around the body, hard to detect, need a sensor in the house.
ALKENES:
- Complete combustion produces carbon dioxide and water.
- Incomplete combustion produces carbon, carbon monoxide and water.
ALCOHOLS:
- Complete combustion produces carbon dioxide and water
- When oxygen is scarce incompletely combustion produces water and carbon or carbon monoxide
Cracking
- Larger saturated hydrocarbon molecules are broken down into smaller, more useful hydrocarbon molecules
- Some are saturated (alkanes), some are unsaturated (alkenes)
Alkenes
- Unsaturated hydrocarbons
- General formula CnH2n
- Functional group C=C, allowing for addition reactions
- Gas at room temp/pressure
Functional group
The reactive group in a molecule
Hydrogenation
Alkene + Hydrogen = Alkane
Alkene + Steam = Alcohol
Requires a catalyst
Testing for alkanes/alkenes
- Bromine water with alkane = no change
- Bromine water with alkene = colourless
Polymer/Polymerisation
- A long chain of molecules made up of small, repeating units
- To produce a long polymer from many small molecules (monomers)
- The C=C bond allows for polymerisation
- Polymers are unreactive, so can store food and chemicals. They are also difficult to dispose of, landfill and inceneration are commonly used.
Alcohols
- General formula CnH2n+1OH
- Functional group -OH
- Liquids at room temp/pressure
Oxidation of alcohols
- Methanol, ethanol and propan-1-ol can be oxidised to produce carboxylic acids.
- Methanol forms methanoic acid
- Ethanol forms ethanoic acid
- Propan-1-ol forms propanoic acid
- They only have to be exposed to air for this to happen
- Can also be oxidised used acidified potassium dichromate solution (mixed in a test tube in a warm bath). Orange changes to green when the alcohol is oxidised
Making ethanol by fermentation
- Produced by fermentation, concentrated in fractional distillation
- Fermentation is an anaerobic process (no air can get in)
- Yeast provides the enzymes needed
- Temperature has to be warm but not too warm (25 - 35 degrees)
- The sugar is dissolved and mixed with yeast
- Process is slow, kills about 15% of the yeast
