C7: Organic chemistry
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What makes something “organic” in the chemical sense?
It contains carbon.
What is crude oil?
• A finite resource found in rocks: the remains of an ancient biomass, consisting mainly of plankton that was buried in mud. • Is a mixture of a large number of compounds, mostly hydrocarbons.
What are hydrocarbons?
Molecules made only of hydrogen and carbon.
Most of the hydrocarbons in crude oil are what?
Alkanes.
What is the general formula for alkanes?
CnH2n + 2
What is meant by the term “homologous series”?
A series of compounds with the same functional group and similar chemical properties.
What are the names of the first four members of the alkanes?
• Methane • Ethane • Propane • Butane
What is fractional distillation and what is its purpose?
• The process by which hydrocarbons in crude oil are separated into fractions. • The fractions can be processed to produce fuels and feedstock for the petrochemical industry.
Explain how the process of fractional distillation works.
• Crude oil is heated until the hydrocarbons evaporate. • The hydrocarbons rise through the column. • The hydrocarbons condense and different fractions are extracted in different parts of the column. • Longer hydrocarbons condense in the lower parts of the column; shorter ones in the upper parts.
Name 5 fuels produced by fractional distillation from crude oil.
• Petrol • Diesel oil • Kerosene • Heavy fuel oil • Liquefied petroleum gases
Name 4 useful materials produced by the petrochemical industry.
• Solvents • Lubricants • Polymers • Detergents
Why is there such a vast array of natural and synthetic carbon compounds?
Carbon atoms have the ability to form families of similar compounds (homologous series).
What 3 properties of hydrocarbons depend on the size of molecules?
• volatility (boiling points) • viscosity (runniness) • flammability
For hydrocarbons, how does boiling point change with increasing molecular size?
• Longer hydrocarbon chains have more cumulative intermolecular forces which require more energy to overcome • So their boiling points are higher • Shorter chains have less cumulative intermolecular forces, so it takes less energy to separate molecules • So they are more volatile
For hydrocarbons, how does viscosity change with increasing molecular size?
• Longer hydrocarbon chains have more cumulative intermolecular forces which require more energy to overcome • So they are more viscous • Shorter chains have less cumulative intermolecular forces, so it takes less energy to separate molecules • So they are less viscous
For hydrocarbons, how does flammability change with increasing molecular size?
• Longer hydrocarbon chains have more cumulative intermolecular forces which require more energy to overcome • So they are less flammable • Shorter chains have less cumulative intermolecular forces, so it takes less energy to separate molecules • So they are more flammable
What happens during the combustion of hydrocarbons?
• The carbon and hydrogen in the fuels are oxidised • Energy is released
Write the general equation for the complete combustion of a hydrocarbon.
Hydrocarbon + oxygen → carbon dioxide + water
What are alkenes?
Hydrocarbons with the functional group C=C (with a double carbon-carbon bond).
What is cracking and what is its purpose?
• The process by which long-chain hydrocarbons are broken down to produce smaller, more useful molecules by thermal decomposition • The products of cracking are alkanes and alkenes • Some of the products of cracking - the small ones - are used for fuels because they are flammable
How are alkenes (produced by cracking) useful?
• Used to produce polymers • Used as starting materials for the production of many chemicals
Name 2 types of cracking.
• Catalytic cracking • Steam cracking
Describe the conditions used for catalytic cracking.
• It is a thermal decomposition reaction • Long-chain hydrocarbons are heated and vaporised • Vapour is passed over a powdered aluminium oxide catalyst • The molecules split apart on the surface of the specks of catalyst
Describe the conditions used for steam cracking.
• It is a thermal decomposition reaction • Long-chain hydrocarbons are heated and vaporised • Vapour is mixed with steam and heated to a very high temperature • The molecules split apart