Organic chemistry

Define ‘hydrocarbon’

A substance made up of ONLY hydrogen and carbon atoms.

What is the alkane formula?

Hn C2n+2

What are the first four alkanes?

Methane, Ethane, Propane, Butane

What is the difference between long chains and short chains? (Viscosity, flammability, boiling point)

Long chains: lower flammability, higher boiling point, higher viscosity

Short chains: higher flammability, lower boiling point, lower viscosity

What is the equation for combustion? (word and balanced symbol)

Hydrocarbon + oxygen → carbon dioxide + water

CH4 + 2O2 → CO2 + 2H2O

How is crude oil formed?

From the remains of plants and animals that died millions of years ago and were buried in mud. With high temperature and pressure, the remains turn into crude oil which can be drilled out of the rocks where its found.

How are the different compounds in crude oil seperated?

Fractional Distillation

How does fractional distillation work?

The oil is heated until it is mostly a gas these enter a fractionating column. In the column there is a temperature gradient, (hotter at bottom, cooler at top). The longer hydricarbons have higher boiling points, they condense into liquids early on at the bottom. The shorter hydrocarbons have a lower boiling point and condense and drain much later, when there at the top of the column. The crude oil mixtures are seperated into different ftavtions. Each fravtion have a similar ammount of carbon atoms, so they have a similar boiking pount.

Fractional distillation fractions from top to bottom.

Natural gas, petrol, kerosene, disel, heavy oil, bitumin

What is cracking?

Large hydrocarbons that are broken down (cracked) to produce smaller and more useful molecules.

Describe the two methods of cracking.

Steam - vapourise them by heating a long chained hydricarbon, mix them with steam and heat to a very high temperature.

Catalytic - vapourise them by heating a long chained hydrocarbon, vapour is passed over a hot powdered aluminium oxide catalyst, the long chained molecules will split apart on the surface of the catalyst.

How do you balance a chemical equation for cracking?

Long chained molecule → shorter alkane (single bond), alkene (double bond)

Whats the difference between alkanes and alkenes?

Alkenes - double bond, unsaturated

Alkane - single bond, saturated

Whats the formula for alkenes?

Cn H2n

Define ‘combustion’

Burning a fuel in oxygen.

What is ‘complete combustion'?

Having plenty of oxygen.

What is ‘incomplete combustion’?

Insufficient ammounts of oxygen.

How do you test for alkenes? Whats the colour change?

Bromine water test

Brown → colourless

What are the uses of crude oil?

Polymers, lubricants, solvents, detergants, fuel.