Alkanes

Fractional Distillation

The crude oil is heated to around 1000 degrees celcius. This causes the majority of the hydrocarbons to vaporise, turning into a high-pressure gas-vapour mixture.

The hot vaporised mixture is then fed into the bottom of the fractionating column, which is hotter at the bottom and cooler at the bottom.

Longer-chained alkanes have the highest boiling points and condense the quickest , so they are collected at the bottom e.g bitumen and lubricating oil

Medium-chained alkanes condense at intermediate temperatures so are collected in the middle e.g kerosene and diesel

Short-chained alkanes have the lowest boiling points so condense at the top e.g refinery gases and petrol

Why are alkanes called a organic homologous series?

Organic compounds contain carbon atoms.A homologous series is a group of carbon compounds with similar features / properties.Homologous series have the same general formula.Alkanes all have the formula CₙH₂ₙ₊₂.Alkanes all have similar properties .Alkanes are all saturated hydrocarbons.

LC alkanes vs SC alkanes Boiling Points

LC alkanes have higher Bps

1) Large surface area for london forces to form

2) More electrons to form london forces

Why are alkanes insoluble in water?

They have no permanent dipoles

Thermal Cracking

High temp and Pressure: 450-900. 70 atm

We get a high percentage of alkenes, which are highly reactive

Catalytic Cracking

High temp= 450 Low Pressure: 1-2 atm ( approx 100-200k Pa)

Uses zeolite catalyst containing a mixture of Aluminium Oxide and Silicon Dioxide

Has a large surface area, making it effective

Products are often branched alkane which is useful for petrol ( as it burns with less soot)

Produces cycloalkanes

What can be made from alkenes?

1) Polymers

2) Plastic

Products from Incomplete combustion

1) Carbon monoxide

2) Particulates/ Pure Carbon

Impurities from Incomplete combustion

1) Sulfur dioxide

2) Nitrogen

What does sulfur dioxide cause?

1) Acid rain

2) Respiratory issues

3) Photochemical smog

What is photochemical smog?

A mixture of secondary pollutants formed from primary precursors.

1) Nitrogen Oxides

2) Volatile Organic Compounds

3) Carbon Monoxide

UV Light

Warm Temp

Stagnant Air

What does Carbon Monoxide and Soot cause?

1) Respiratory issues

2) Global dimming

Flue gas desulfurisation

We get rid of flue gases such as Sulfur dioxide and Carbon monoxide by

1) A slurry of calcium carbonate (limestone, CaCO₃) or calcium oxide (quicklime, CaO) in water is used.

2) The acidic gases are dissolved in the slurry and neutralised by the base.

3) This forms Calcium sulfate dihydrate (Gypsum) a product used in plaster and building materials

What is the other way we get rid of NOx?

To prevent NOx forming in Car engines (as they have high temperatures). There is a catalytic converter which has a ceramic honeycomb coated with a thin layer of metal- to give it a large surface area.

What are the metals that can be used to coat the ceramic honeycomb?

1) Palladium

2) Rhodium

3) Platinum

Suggest two reasons why alkanes are generally unreactive

1) They are non-polar molecules as Carbon and Hydrogen have very similar electronegativity.

2) The bonds in alkanes are very strong and require lots of energy to break.

What are the three steps of free radical substution of alkanes?

Initation, Propagation and Termination