Syllabus Points

Organic Chemistry:

4.1 know that a hydrocarbon is a compound of hydrogen and carbon only

4.2 understand how to represent organic molecules using empirical formulae, molecular formulae, general formulae, structural formulae and displayed formulae

4.3 know what is meant by the terms homologous series, functional group and isomerism

4.4 understand how to name compounds relevant to this specification using the rules of International Union of Pure and Applied Chemistry (IUPAC) nomenclature

4.5 understand how to write the possible structural and displayed formulae of an organic molecule given its molecular formula

4.6 understand how to classify reactions of organic compounds as substitution, addition and combustion

4.7 know that crude oil is a mixture of hydrocarbons

4.8 describe how the industrial process of fractional distillation separates crude oil into fractions

4.9 know the names and uses of the main fractions obtained from crude oil:refinery gases, gasoline, kerosene, diesel, fuel oil and bitumen

4.10 know the trend in colour, boiling point and viscosity of the main fractions

4.11 know that a fuel is a substance that, when burned, releases heat energy

4.12 know the possible products of complete and incomplete combustion of hydrocarbons with oxygen in the air

4.13 understand why carbon monoxide is poisonous, in terms of its effect on the capacity of blood to transport oxygen

4.14 know that, in car engines, the temperature reached is high enough to allow nitrogen and oxygen from air to react, forming oxides of nitrogen

4.15 explain how the combustion of some impurities in hydrocarbon fuels results in the formation of sulfur dioxide

4.16 understand how sulfur dioxide and oxides of nitrogen contribute to acid rain

4.17 describe how long-chain alkanes are converted to alkenes and shorter-chain alkanes by catalytic cracking (using silica or alumina as the catalyst and a temperature in the range of 600–700ºC)

4.18 explain why cracking is necessary, in terms of the balance between supply and demand for different fractions

4.19 know the general formula for alkanes

4.20 explain why alkanes are classified as saturated hydrocarbons

4.21 understand how to draw the structural and displayed formulae for alkanes with up to five carbon atoms in the molecule, and to name the unbranched-chain isomers

4.22 describe the reactions of alkanes with halogens in the presence of ultraviolet radiation, limited to mono-substitution

4.23 know that alkenes contain the functional group >C=C<

4.24 know the general formula for alkenes

4.25 explain why alkenes are classified as unsaturated hydrocarbons

4.26 understand how to draw the structural and displayed formulae for alkenes with up to four carbon atoms in the molecule, and name the unbranched-chain isomers

4.27 describe the reactions of alkenes with bromine to produce dibromoalkanes

4.28 describe how bromine water can be used to distinguish between an alkane and an alkene

4.28 describe how bromine water can be used to distinguish between an alkane and an alkene

Testing for alkenes:
- test for alkene: bromine water (orange)
- if you shake alkene with bromine water, then bromine water turns colorless.

The reaction that takes place in this is an addition reaction.

4.17 describe how long-chain alkanes are converted to alkenes and shorter-chain alkanes by catalytic cracking (using silica or alumina as the catalyst and a temperature in the range of 600–700ºC)

- In cracking, a large alkane is cracked to produce smaller, more useful molecules.

• longer chained alkane --> shorter chained alkane + alkene
• OR: longer chained alkane --> alkene + hydrogen
• OR: longer chained alkane --> alkane + alkane + alkene

Why do we crack alkanes?
- shorter chained alkanes are used for fuels
- shorter chained alkenes are used for plastic production

Explanation:
- cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules
- fractions containing large hydrocarbons are heated at 600-700℃ to vaporize them
- vapours will pass over the hot catalyst of silica/alumina
- this process breaks covalent bonds in molecules, causing thermal decomposition reactions
- as a result, cracking produces smaller alkanes and alkenes.
e.g. decane --> octane + ethene

Conditions of Cracking;
2 ways of cracking:
- catalytic cracking: using heat and a catalyst. The catalyst speeds up the reaction
- steam cracking: using heat and steam.

4.25 explain why alkenes are classified as unsaturated hydrocarbons

Saturated: a molecule containing only single bonds between carbon atoms.
e.g. alkanes

Unsaturated: a molecule of C=C double bond.
e.g. alkenes

So in summary, alkanes are saturated and alkenes and unsaturated

4.24 know the general formula for alkenes

General formula for alkenes:

C_nH_2n

4.5 understand how to write the possible structural and displayed formulae of an organic molecule given its molecular formula

Displayed formula: type of structural formula and shows all the bonds in the molecule as individual lines, where each line represents a pair of shared electrons.
 


 Structural Formula: