4.7 know that crude oil is a mixture of hydrocarbons

Crude oil is a mixture of hydrocarbons

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

Alkanes react with bromine in presence of UV light. In this reaction, a hydrogen atom in the alkane is replaced by a bromine atom, hence it is a SUBSTITUTION reaction.
- In a substitution reaction, one atom is swapped with another atom.
- All Alkanes undergo a substitution reaction with halogens under UV light.
e.g. methane reaction with bromine:

4.20 explain why alkanes are classified as saturated 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

4.19 know the general formula for alkanes

General formula for alkanes:

C_nH_2n+2

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

Acids formed in the atmosphere can fall as acid rain. This can harm the environment and can also destroy limestone buildings and marble statues since they are made of limestone (Calcium Carbonate CaCO₃). Metals like iron are also attacked by acid rain.

- Sulfur dioxide in atmosphere from burning of fossil fuels can react with water and oxygen to make sulfuric acid (H₂SO₄):
2SO₂ (g)         +         2H₂O (l)         +         O₂ (g)         →         2H₂SO₄ (aq)

- If sulfur dioxide in the atmosphere reacts with just water, a weaker acid sulfurous acid (H₂SO₃) is formed:
SO₂ (g)         +         H₂O (l)         →         H₂SO₃ (aq)

- In car engines the temperature is high enough for nitrogen in air to react with oxygen to produce oxides of nitrogen, e.g:
N₂ (g)         +         O₂ (g)         →         NO₂ (g)
In the atmosphere these nitrogen oxides can produce nitric acid (HNO₃).

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

Fuels are derived from crude oil.
- Although these fuels are hydrocarbons, they include impurities such as sulfur.
- When the fuels are burned, sulfur dioxide is produced which can escape into the atmosphere.
S (s)         +         O₂ (g)         →         SO₂ (g)

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

When fuels are burnt in vehicle engines, a high temperature is reached. At these high temps, nitrogen and oxygen from air react to produce nitrogen oxides.