The reactivity series

Metals can be put in order of how reactive they are. We deduce this from how vigorously they react with water and dilute acids — the more reactive a metal, the more readily its atoms form positive ions (cations). Carbon and hydrogen (both non-metals) are slotted in as reference points.

Watch out: carbon and hydrogen aren't metals — they're put in the list only as reference markers so you can compare a metal's reactivity to them.

Deduce the reactivity

Oxidation & reduction

At Foundation level, redox is defined in terms of oxygen:

• Oxidation = gain of oxygen.
• Reduction = loss of oxygen.

So when an ore (a metal oxide) is turned into the metal, the metal is reduced — oxygen is removed. That is why extraction of metals always involves reduction of the ore.

Higher tier (4.2): redox is also defined by electrons — remember OIL RIG: Oxidation Is Loss of electrons, Reduction Is Gain of electrons. The two definitions agree.

Oxidation or reduction?

Tap whether each change is oxidation or reduction.

Where metals come from

• Most metals are found combined in compounds in rocks — these rocks are called ores, and most metals are extracted from them.
• Unreactive metals (like gold) are found in the Earth's crust as the uncombined (native) elements — they don't react, so they stay as pure metal.

A metal's resistance to oxidation (e.g. resistance to corrosion) follows its place in the reactivity series: the less reactive a metal, the more it resists being oxidised, which is why gold stays shiny while iron rusts (spec 4.9).

Choosing the extraction method

How you extract a metal depends on its position in the reactivity series (and the cost of the process):

• Metals less reactive than carbon can be extracted by heating the ore with carbon (carbon reduces the oxide). Example: iron.
• Metals more reactive than carbon can't be displaced by carbon, so they're extracted by electrolysis — which uses lots of electricity and is therefore more expensive. Example: aluminium.

Why discovery dates link to this: metals you can get just by heating with carbon (iron, copper) were known for thousands of years. Reactive metals like aluminium needed electrolysis, only possible once we could generate electricity — so they were discovered much later and stayed costly.

(Knowledge of the blast furnace is not required for 1CH0.)

Which method?

Redox as electron transfer

Biological extraction

Some ores are low-grade — they contain very little metal, so normal extraction is wasteful. Two greener, biological methods can get metals (e.g. copper) from them:

Also: displacement with scrap iron. Copper can be obtained from copper salt solutions by adding cheap scrap iron — iron is more reactive, so it displaces the copper: Fe + CuSO₄ → FeSO₄ + Cu.

Match the method

Tap a method on the left, then its correct description on the right.

Recycling metals

Recycling metals (rather than extracting new ones from ore) has big advantages:

• Conserves resources — ores are finite, so recycling preserves the supply of valuable raw materials.
• Saves energy & money — recycling usually uses far less energy than extracting from ore (e.g. recycling aluminium uses a fraction of the electricity that electrolysis needs).
• Protects the environment — less mining, less quarrying, less waste tip, fewer emissions.

Economic point: extracting reactive metals is energy-hungry and expensive, so recycling them is especially worthwhile.

Life cycle assessment (LCA)

A life cycle assessment works out the total environmental impact of a product across its whole life — four stages:

• 1. Getting the raw materials — mining, quarrying, extraction.
• 2. Manufacturing the product (and packaging).
• 3. Using the product.
• 4. Disposing of it when it's no longer useful (landfill, recycling).

You should be able to evaluate data from an LCA — comparing, say, a plastic bag vs a paper bag across all four stages, not just one.

(LCA is part of Edexcel Topic 4, statements 4.11–4.12.)

An LCA stage

Reversible reactions

In a reversible reaction, the products can react to remake the reactants. We show this with the special ⇌ symbol instead of a single arrow:

Changing the conditions (temperature, concentration, pressure) can change which direction is favoured. A classic example is heating hydrated copper sulfate:

Energy is mirrored: if the forward reaction is exothermic (gives out energy), the backward reaction is endothermic (takes in the same amount), and vice-versa.

Dynamic equilibrium

In a closed system (nothing in or out), a reversible reaction reaches dynamic equilibrium: the forward and backward reactions are still happening, but at the same rate, so the amounts of reactants and products stop changing.

Worked example — the Haber process (spec 4.15–4.16): N₂ (from air) + 3H₂ (from natural gas) ⇌ 2NH₃ (ammonia), run at 450 °C, 200 atmospheres, with an iron catalyst.

What "dynamic" means

Shifting the equilibrium

If you change the conditions on a system at equilibrium, the position shifts to oppose that change (Le Chatelier's idea). You need to predict the effect of changing temperature, pressure and concentration:

• Temperature ↑ → shifts in the endothermic direction (takes in the added heat).
• Pressure ↑ (gases) → shifts towards the side with fewer gas molecules.
• Concentration of a reactant ↑ → shifts towards the products to use it up.

Misconception fix: the system always shifts to oppose the change you made — heat it and it absorbs heat; squeeze it and it takes up less volume. It is not "moving with" the change.

Predict the shift

The Topic 4 essentials

You've now covered all of Edexcel 1CH0 Topic 4 — Extracting metals and equilibria. Press Finish to see your score.