Singapore-Cambridge N(A)-Level Combined Science, Chemistry: Metals and Organic, from the reactivity series and metal extraction to crude oil, alkanes, combustion and air pollution

What this module is about

The Metals and Organic module of N(A)-Level Combined Science Chemistry (SEAB 5105 and 5107) is about useful materials and the cost of using them. It ranks metals by how readily they react, uses that ranking to explain how each is extracted, then turns to fuels from crude oil and the gases their burning releases into the air. The thread is reactivity: how reactive a metal is, how readily a fuel burns, and how the products affect the atmosphere.

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 and extracting metals

The module starts with the reactivity series and extraction of metals. Metals can be placed in order of reactivity from how vigorously they react, for example with water or acid, and from displacement reactions in which a more reactive metal pushes a less reactive one out of its compound. Reactivity decides the extraction method: very reactive metals (such as aluminium) need electrolysis; moderately reactive metals (such as iron) can be reduced with carbon; and unreactive metals (such as gold) are found native.

Crude oil, alkanes and combustion

Next comes organic chemistry, fuels and alkanes. Crude oil is a mixture of hydrocarbons separated into useful fuels. The alkanes are a family of hydrocarbons made only of carbon and hydrogen. Burning them in plenty of oxygen gives complete combustion, producing carbon dioxide and water and releasing the most energy; burning them in limited oxygen gives incomplete combustion, producing toxic carbon monoxide and soot and releasing less energy.

The atmosphere and air pollution

The module finishes with the atmosphere and air pollution. Clean dry air is roughly four-fifths nitrogen and one-fifth oxygen, with small amounts of other gases including carbon dioxide. Burning fuels adds pollutants: carbon monoxide (toxic), sulfur dioxide (causes acid rain) and oxides of nitrogen. Carbon dioxide is a greenhouse gas: it traps heat the Earth radiates, warming the lower atmosphere, and rising levels are linked to climate change.

How this module is examined

• Justify the extraction method by reactivity. Electrolysis for very reactive metals, reduction with carbon for moderately reactive ones, and native for unreactive ones.
• Name the right combustion products. Carbon dioxide and water for complete; carbon monoxide and soot for incomplete.
• Match each pollutant to its source and effect. For example, sulfur dioxide from burning sulfur-containing fuels causes acid rain.

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 if a more reactive metal is added to a solution of a less reactive metal's salt. (1 mark)
2. Explain why aluminium is extracted by electrolysis but iron can be extracted with carbon. (2 marks)
3. Name the two products of the complete combustion of a hydrocarbon. (2 marks)
4. State one product of incomplete combustion and why it is dangerous. (2 marks)
5. Give the approximate composition of clean dry air. (2 marks)
6. Name one air pollutant, its source and one effect. (2 marks)