Reactivity series: order and evidence
The reactivity series ranks metals by how readily they lose electrons (K > Na > Ca > Mg > Al > [C] > Zn > Fe > [H] > Cu > Ag > Au). Three lines of evidence build it: reaction with water (K/Na/Ca react with cold water, Mg very slowly); reaction with dilute acid (more reactive metals fizz faster → salt + hydrogen; copper does not react); and displacement (a more reactive metal displaces a less reactive one from its salt solution).
Oxidation/reduction: oxygen and electrons
Oxidation = gain of oxygen OR loss of electrons; reduction = loss of oxygen OR gain of electrons (OIL RIG). A redox reaction has both together. The oxidising agent is itself reduced (takes electrons / gives oxygen); the reducing agent is itself oxidised. Displacement is redox: zinc added to is oxidised (the reducing agent), copper ions reduced. Always name the exact species — a metal oxide loses oxygen, not the metal atom.
Rusting: needs water and oxygen; 3 preventions
Rusting is the corrosion of iron; it needs both water and oxygen — remove either and it stops. Rust is hydrated iron(III) oxide. Three preventions: barrier methods (paint, oil, plastic) keep water and oxygen off but fail once scratched; galvanising coats iron with zinc — a barrier that also gives sacrificial protection because zinc is more reactive; sacrificial protection attaches a more reactive metal (zinc/magnesium) that corrodes in preference.
Drawn from real examiner reports.
Name the OXIDE, not the metal
The top marks-loser on oxygen-redox. When a metal oxide is reduced by carbon, it is the metal oxide that loses oxygen — not the metal atom, which has no oxygen to lose. Write "iron(III) oxide loses oxygen → reduced", never "iron loses oxygen and is reduced". Then name the species that gains oxygen and is oxidised: carbon gains oxygen → oxidised.
Jun24 1CR Q12ci: name the OXIDE that loses oxygen, not the metal
Name BOTH oxidation and reduction
When you describe a redox reaction as a whole, naming only oxidation OR only reduction is not enough — both are needed. Say which species is oxidised AND which is reduced (or give the reaction-type name). A bare "it is a redox reaction" or "they happen at the same time" with no species identified scores nothing.
Jun23 Q2ci; Jun24 1CR Q2d: both oxidation and reduction needed
Rust is iron(III) oxide — keep the (III)
Rust is iron(III) oxide — the oxidation state (III) is frequently dropped. "Iron(II) oxide", "iron hydroxide", "iron oxide" without the (III), or naming a process (oxidation) instead of the compound, all lose the mark. Learn the full name: rust is hydrated iron(III) oxide.
Nov24 Q3aii; Jun23 Q2ai: the (III) in iron(III) oxide is often missing
Coating protects as a BARRIER
Rust prevention needs the right words. A coating works as a barrier, keeping water and oxygen off the iron — "covering" or "coating" alone loses the point. For sacrificial protection, zinc is more reactive than iron and corrodes in its place; do not write that "the zinc rusts" — only iron rusts, and zinc protects it by corroding preferentially.
Nov24 Q3bi: "barrier" needed; Q3biii: zinc does not rust
Sulfate (SO4), not sulfide or sulfite
The salt from a metal and sulfuric acid is a sulfate (): zinc + sulfuric acid → zinc sulfate . Wrong anions lose the mark — sulfide (, no oxygen), sulfite (, one oxygen fewer), or an invented "sulfur oxide". Acid → salt: hydrochloric → chloride, sulfuric → sulfate, nitric → nitrate.
Show the reaction is finished by no more gas
In the metal + acid practical, "the reaction has finished" needs an observation: no more gas collects / the gas syringe stops / bubbling stops. Restating "the reaction has finished" or "the metal is used up" scores zero. When the metal is in excess it need not be weighed — the acid is the limiting reactant, so the extra metal remains unreacted.
Name the salt from the acid
For metal + acid questions: metal + acid → salt + hydrogen. Name the salt from the acid — hydrochloric → chloride, sulfuric → sulfate, nitric → nitrate. Remember copper is below hydrogen, so copper gives no reaction with dilute acid.
Label every species: gain/loss + verdict
Redox marks are awarded per species. For each species state what it gains or loses (oxygen or electrons) AND the verdict (oxidised / reduced). For electron questions use OIL RIG: the species that loses electrons is oxidised, the one that gains them is reduced.
Match oxygen- or electron-language
Match your language to the question. An oxygen-based question () is answered in oxygen language; an ion or electron question (displacement) in electron language. Give the full two-part definition and do not swap mid-answer.
Deduce the order from the evidence
To rank metals, use the evidence: the more vigorously a metal reacts with water or dilute acid, the more reactive it is; and a metal that displaces another from its salt solution is the more reactive of the two. Build the order from the observations rather than reciting it blind.
The reactivity series ranks metals in order of how readily they react (how readily they lose electrons to form positive ions).
Order for 4SD0 (most → least reactive):
Carbon (C) and hydrogen (H) are non-metals shown for reference (they matter for extraction and for which metals react with acid).
Two-element mark-scheme definitions:
| Term | Definition (both elements required) |
|---|---|
| Oxidation | Gain of oxygen OR loss of electrons |
| Reduction | Loss of oxygen OR gain of electrons |
| Redox reaction | A reaction in which oxidation and reduction happen at the same time |
| Oxidising agent | The species that is reduced (it removes electrons from / gives oxygen to another species) |
| Reducing agent | The species that is oxidised (it gives electrons to / removes oxygen from another species) |
| Displacement | A more reactive metal takes the place of a less reactive metal in a solution of its salt |
| Sacrificial protection | Protecting iron by attaching a more reactive metal that corrodes in preference to it |
OIL RIG = Oxidation Is Loss, Reduction Is Gain (of electrons). This is a mnemonic, not a definition — write out the full definition for marks.
Salt naming (metal + acid): hydrochloric acid → chloride; sulfuric acid → sulfate (); nitric acid → nitrate.
Copper is below hydrogen, so copper does not react with dilute acid.
Define oxidation (give both mark-scheme forms).
Zinc reacts with dilute sulfuric acid to form zinc sulfate, .
Calculate the relative formula mass () of zinc sulfate. (: Zn = 65, S = 32, O = 16)
