Chemical Changes

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infoWhy this? Patterns in metal reactivity allow us to predict displacement reactions, explain oxidation and reduction, and select appropriate extraction methods. A more quantitative treatment of acids and pH also clarifies neutralisation, salt formation, and the distinct meanings of strength and concentration.

scheduleWhy now? This unit builds directly on Year 8 acids and alkalis and on Year 9 atomic structure, ions, equations, and conservation of mass. These foundations allow reactions to be explained through electron transfer and hydrogen-ion concentration, while reactivity is later reinforced through periodic patterns.

The reactivity series is a list of metals ordered by their reactivity, from most to least reactive, for example: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, copper.
A displacement reaction is a chemical reaction in which a more reactive metal displaces a less reactive metal from its compound.
In a displacement reaction, the more reactive metal is oxidised (loses electrons or gains oxygen) and the less reactive metal is reduced (gains electrons or loses oxygen).
Oxidation is the gain of oxygen or loss of electrons, and reduction is the loss of oxygen or gain of electrons.
The reactivity series determines the method of metal extraction: highly reactive metals are extracted by electrolysis, less reactive metals by reduction with carbon, and unreactive metals may be found native.
In metal extraction, the metal oxide is reduced to form the metal, and the reducing agent is oxidised.
Neutralisation is a reaction in which an acid reacts with a base to form a salt and water.
The terms dilute and concentrated refer to the amount of acid or alkali dissolved in a given volume of water (concentration).
The terms weak and strong refer to the degree of ionisation of an acid or alkali in water: strong acids or alkalis fully ionise, weak acids or alkalis only partially ionise.
The salt produced in a neutralisation reaction depends on the acid and base used, for example: hydrochloric acid + sodium hydroxide → sodium chloride + water.
The concentration of hydrogen ions in a solution determines its pH: as the concentration of hydrogen ions increases, pH decreases.
The pH scale is logarithmic: each decrease of 1 pH unit represents a tenfold increase in hydrogen ion concentration.

rocket_launchYou must be able to

Use observations from practical experiments, such as metal and salt solution reactions, to place metals in the correct order in the reactivity series.
Write word and symbol equations for displacement and neutralisation reactions, identifying reactants and products.
Use the reactivity series to predict and explain the outcomes of displacement reactions.
Identify which substances are oxidised and which are reduced in metal extraction and displacement reactions.
Explain, using equations, how oxidation and reduction occur in terms of oxygen transfer and electron transfer.
Name the salt formed from a given acid and base, for example: nitric acid + potassium hydroxide → potassium nitrate + water.
Distinguish between dilute and concentrated, and weak and strong acids or alkalis, giving examples and explanations.
Quantitatively relate the concentration of hydrogen ions to pH using the formula `\mathrm{pH} = -\log_{10}[\mathrm{H}^+]`.
Evaluate the suitability of specific metal extraction processes based on the position of the metal in the reactivity series and economic or environmental factors.

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