GCSE Combined Science Reactivity & redox revision

Carbon and hydrogen are not metals but they earn their places as reference lines: carbon can strip the oxygen from the ore of any metal below it in the series, and any metal above hydrogen fizzes with dilute acids. Reactivity measures how readily a metal loses electrons to form positive ions — the very definition that makes Group 1 metals the champions.

A metal above hydrogen reacts with dilute acid: metal + acid → salt + hydrogen. The louder the fizz, the more reactive the metal. Magnesium fizzes furiously with dilute hydrochloric acid; zinc bubbles steadily; copper sits in silence. With water, only the top rank reacts at room temperature: potassium snarls, sodium darts, calcium fizzes gently — metal + water → metal hydroxide + hydrogen. Magnesium needs hot water or steam; iron barely rusts its way through.

Put an iron nail into blue copper sulfate solution and the nail coats in copper while the solution fades to green (iron sulfate): iron + copper sulfate → iron sulfate + copper. Iron is more reactive, so it displaces copper. Reverse the experiment — copper wire in iron sulfate — and nothing happens. Each displacement is a redox reaction: iron atoms are oxidised to iron ions; copper ions are reduced to copper atoms.

In oxygen language: oxidation = gaining oxygen; reduction = losing oxygen. Copper oxide + carbon → copper + carbon dioxide has both in one reaction: carbon gains oxygen (oxidised), copper oxide loses it (reduced) — a redox reaction, the reduction half doing the extraction work.

(Higher) In electron language: oxidation is loss of electrons, reduction is gain — OIL RIG. When iron displaces copper, each iron atom loses 2 electrons (Fe → Fe²⁺ + 2e⁻, oxidised) and each Cu²⁺ ion gains them (Cu²⁺ + 2e⁻ → Cu, reduced). The transferred electrons travel from the metal to the ion — redox always comes in pairs.

Most metals are dug up as ores — compounds like oxides. Extraction means reducing the metal ion to the metal. For metals below carbon in the series, cheap carbon does the job: zinc oxide + carbon → zinc + carbon dioxide. Iron is extracted on an industrial scale the same way in the blast furnace. Metals above carbon — aluminium is the famous case — cannot be reduced by carbon because carbon is the less reactive of the two, so they are extracted by electrolysis, which costs far more energy and money.

At the bottom of the table, gold and platinum are so unreactive that they exist native — as pure metal in the Earth, panned from rivers or mined directly, needing no chemistry at all to be useful.

High-grade ores run out, so low-grade leftovers can still yield metal. Phyto­mining plants absorb copper ions from low-grade ore or ash as they grow; the crop is harvested, burned, and the ash’s copper ions are recovered by electrolysis or displacement with scrap iron. Bioleaching uses bacteria that convert insoluble metal compounds into a leachate solution of soluble metal ions, again recovered by electrolysis or displacement.

Both methods are slow and operate at low concentrations, but they extract metal from waste that would otherwise be discarded, reduce the need for new mining, and disturb less land. Traditional mining and extraction remain faster and suit large-scale demand — the evaluation always balances these sides.