Crude Oil, Hydrocarbons, and Chemical Processes
Crude Oil and Fractional Distillation
Crude oil is a complex mixture of hydrocarbons (compounds containing hydrogen and carbon only). Crude oil is separated by fractional distillation in a continuous process, taking off the samples at different levels from the fractionating column. The dissolved gases come out of the top, and the boiling points rise as one goes down the column.
- Refinery gases: Used for bottled gases such as gas, propane, butane
- Gasoline: Fuel for cars (petrol)
- Kerosene: Fuel for jet planes
- Diesel: For lorries and larger cars
- Fuel oil: For heating homes and factories
- Bitumen: For making roads and tar
Alkanes, Alkenes, and Isomers
The alkanes: CnH2n+2. Saturated: Single bond. Isomers: When two or more different compounds have the same molecular formula but different structures.
Cracking: This is an example of thermal decomposition; it gives shorter alkanes, which are more useful.
Alkene: CnH2n Unsaturated: Double bond.
With bromine: Orange to colorless through UV light
Polymers
Poly(propene) for plastic crates and ropes (since it is stronger and less flexible than poly(ethane) and the fibers in ropes are flexible)
Poly(chloroethene), or PVC, for drain pipes and for insulation on electric cables (since it is strong but flexible, and does not conduct electricity).
Alcohols and Carboxylic Acids
Alcohols: CnH2n+1OH Ethanol can be made from ethane and steam. High temperature, a catalyst (phosphoric acid) and high pressure are needed. The ethene combines with steam to produce ethanol, which is used as a solvent. Carboxylic Acids: COOH (CO2H)
Properties of Hydrocarbons
As the molecules get bigger:
- Boiling point increases.
- The liquids become less volatile.
- The liquid flows less easily (they become more viscous).
- Bigger hydrocarbons do not burn as easily as smaller ones.
Chemical Calculations
Amount of substance (mol) = mass (g)/ molar mass (g/mol)
Mass (g) = amount (mol) × molar mass (g/mol)
Avogadro Constant: 6×1023
% Yield = actual amount of desired chemical obtained/ maximum theoretical amount formed x 100
Volume of gas at r.t.p = (number of moles) × 24 dm3
= (Number of moles) × 24000 cm3
Number of moles of gas at r.t.p = volume of gas in dm3 / 24
= Volume of gas in cm3/ 24000
Concentration (mol/dm3) = amount(mol)/volume(dm3)
Amount (mol) = volume (dm3) × concentration (mol/dm3)
Volume(dm3) = amount(mol)/concentration(mol/dm3)
Titration
A pipette is used to measure exactly 20.0 cm3 of the acid, and this is transferred to a conical flask. 2-3 drops of indicator are added: it remains colorless. A burette is filled with sodium hydroxide of known concentration. The initial volume is read, then the tap is opened to add NaOH, rapidly at first, but dropwise near the end-point until there is a permanent pink color.
Electrolysis
Electrolysis is the process of decomposing (breaking down) an ionic substance, called an electrolyte, into simpler substances using electricity.
Cathode: If the metal is more reactive than hydrogen, hydrogen is formed. If it is less reactive, the metal is formed.
Anode: If a concentrated solution of a halide (compound with Cl, Br, I) is present, then Cl, Br, or I is formed. If the halide solution is dilute, oxygen is formed.