Singapore-Cambridge GCE O-Level Combined Science, Chemistry: Metals and Organic Chemistry, from the reactivity series and the extraction of metals to alkanes, alkenes, alcohols and carboxylic acids

What this module is about

Metals and Organic Chemistry brings together two strands of descriptive chemistry that both reward pattern recognition. The metals strand is governed by reactivity: order the metals, and you can predict displacement reactions and choose the right method to extract each metal from its ore. The organic strand is governed by structure: organise carbon compounds into homologous series, and the reactions of each family follow from their bonding. The connecting idea is that a single ordering principle, reactivity for metals, structure for organic compounds, lets you predict behaviour instead of memorising it case by case.

This overview pulls the threads together and links to every dot point page in the module, each with its own worked answers and practice questions.

The reactivity series

The metals strand opens with the reactivity series. Metals are placed in order of reactivity from how vigorously they react with water, acids and oxygen, giving the familiar list from potassium and sodium at the top down to copper, silver and gold at the bottom. The order predicts displacement: a more reactive metal displaces a less reactive one from a solution of its salt, because it forms positive ions more readily. This single rule explains a large set of reactions and is regularly tested with displacement experiments.

Extracting metals

Reactivity then determines extraction in extraction of metals. A metal below carbon in the series, such as iron, can be reduced from its oxide by heating with carbon in the blast furnace, a relatively cheap process. A metal above carbon, such as aluminium, cannot be reduced by carbon and must be extracted by electrolysis of its molten oxide, which is far more energy-intensive. The principle, the more reactive the metal the harder it is to extract, ties the whole topic back to the reactivity series.

Hydrocarbons: alkanes and alkenes

The organic strand begins with alkanes, alkenes and the homologous series. A homologous series is a family of compounds sharing a general formula and similar chemistry, each member differing by CH2. Alkanes are saturated (single bonds, general formula CnH2n+2) and fairly unreactive, undergoing combustion and substitution. Alkenes are unsaturated (a carbon-carbon double bond, general formula CnH2n) and more reactive, undergoing addition. The bromine test distinguishes them: alkenes rapidly decolourise orange bromine water, alkanes do not.

Alcohols and carboxylic acids

Finally, alcohols and carboxylic acids covers two oxygen-containing families. Ethanol, the best-known alcohol, is made by fermentation of glucose or by the addition of steam to ethene, and burns and can be oxidised to ethanoic acid. Carboxylic acids such as ethanoic acid show typical acid reactions, and an alcohol reacts with a carboxylic acid to form an ester (esterification), the reaction behind many fruity smells. Recognising each family from its functional group, the OH of alcohols and the COOH of carboxylic acids, is the key skill.

How this module is examined

• Use the reactivity series as a prediction tool. For displacement and extraction, name the more reactive metal and state that it displaces or resists reduction accordingly.
• Match the test to the bond. The bromine water test for unsaturation (rapid decolourisation by an alkene) is a recurring question; state the colour change.
• Identify families from functional groups. Spot the C=C of an alkene, the OH of an alcohol and the COOH of a carboxylic acid, and link each to its characteristic reaction.

Check your knowledge

A mix of recall and application questions covering the module. Attempt them under timed conditions, then check against the solutions, and use the dot point pages for fuller practice.

1. State what is observed when iron is added to copper(II) sulfate solution, and explain why. (2 marks)
2. Explain why aluminium is extracted by electrolysis rather than by heating with carbon. (2 marks)
3. State the general formula of the alkanes and of the alkenes. (2 marks)
4. Describe the bromine water test and its result for an alkene. (2 marks)
5. Name the product when ethanol is oxidised, and name the type of compound it is. (2 marks)
6. Name the type of compound formed when an alcohol reacts with a carboxylic acid. (1 mark)