7.1.1Organic Chemistry
Crude Oil, Hydrocarbons and Alkanes — AQA GCSE Combined Science Trilogy 8464 - Chemistry Revision Notes & Topical Questions
5 min read 7 parts Lesson 2 of 5
Section 1 of 7Crude oil
1Dead plankton
- Dead plankton Millions of years ago tiny marine organisms died and sank to the sea bed.
2Buried in mud
- Buried in mud Layers of sediment covered the remains, trapping them without oxygen.
3Heat and pressure
- Heat and pressure Over millions of years these conditions turned the remains into crude oil.
4Finite resource
- Finite resource Crude oil forms far more slowly than it is used, so it is non-renewable.
Section 2 of 7What is crude oil?
A mixture
- A mixture Crude oil is a mixture of many different compounds that are not chemically joined to each other.
- Each compound keeps its own properties, which is why the parts can be separated.
Mostly hydrocarbons
- Mostly hydrocarbons Most of the compounds are hydrocarbons: molecules made of hydrogen and carbon atoms only.
- Many of them are alkanes.
Section 3 of 7The alkanes
| Name | Formula | Carbon atoms |
|---|---|---|
| Methane | CH4 | 1 |
| Ethane | C2H6 | 2 |
| Propane | C3H8 | 3 |
| Butane | C4H10 | 4 |
Section 4 of 7Features of alkanes
Alkane family
General formula
- General formula Alkanes follow CnH2n+2, so with 5 carbons the formula is C5H12.
Saturated
- Saturated Every carbon-carbon bond is a single covalent bond, so no more atoms can be added.
Homologous series
- Homologous series They share the same general formula and similar chemical properties, with a gradual change in physical properties.
Names
- Names The first four have special names;
- after that the prefixes pent-, hex-, hept- and so on show the carbon count, all ending in -ane.
Section 5 of 7Drawing an alkane
1
Decide how many carbon atoms there are from the name, for example propane has three.
2
Draw the carbon atoms in a chain, joined by single lines.
3
Add hydrogen atoms so that each carbon has exactly four bonds in total.
4
Check the count against CnH2n+2; propane gives C3H8.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Hydrocarbon | A compound containing only hydrogen and carbon atoms. |
| Alkane | A saturated hydrocarbon with only single bonds between carbon atoms. |
| Saturated | Containing only single carbon-carbon bonds. |
| Homologous series | A family of compounds with the same general formula and similar chemical properties. |
| Finite resource | A resource that will run out because it cannot be replaced as quickly as it is used. |
| Mixture | Two or more substances that are not chemically combined. |
Section 7 of 7Exam technique
1
Saying that crude oil is a compound; it is a mixture of compounds.
2
Describing hydrocarbons as containing hydrogen, carbon and oxygen.
3
Giving an alkane too few hydrogenseach carbon must form four bonds in total.
4
Writing that crude oil came from dead dinosaurs or from plants alone, rather than ancient marine organisms.
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