The Reactivity Series

Almost half the marks in the Metals topic trace back to one ordered list. Get the reactivity series wrong by a single element and every prediction built on it (displacement, extraction, acid reactions) fails in sequence. Examiner reports repeat the same finding: students who recite the series correctly still misuse the carbon and hydrogen markers, which is where the real marks sit.

The series, in full

Most reactive to least reactive:

Potassium > Sodium > Calcium > Magnesium > Aluminium > (Carbon) > Zinc > Iron > (Hydrogen) > Copper > Silver > Gold

Reactivity here means tendency to form positive ions: the more reactive the metal, the more readily its atoms lose electrons. That single definition powers everything below.

The two bracketed non-metals are decision markers, not metals:

Marker	Decides	Rule
Carbon	Extraction method	Metals below carbon: oxide reduced by carbon. Metals above: electrolysis
Hydrogen	Acid reactions	Metals above hydrogen react with dilute acids to give H2. Metals below do not

So zinc and iron are extracted by carbon reduction, aluminium by electrolysis; the chemistry behind both is on the extraction page. Copper, silver and gold sit below hydrogen, which is why dropping copper into dilute hydrochloric acid produces nothing.

Evidence for the order

The order is not memorised arbitrarily; it comes from comparing reactions, and 0620 expects you to run the comparison both ways (order → prediction, observations → order):

• Cold water: potassium, sodium and calcium react (hydroxide + hydrogen). Magnesium barely reacts with cold water but reacts quickly with steam (oxide + hydrogen). Zinc and iron react with steam slowly; copper not at all.
• Dilute acids: magnesium fizzes violently, zinc steadily, iron slowly, copper not at all.

Given an unfamiliar metal X that reacts with dilute acid but not with cold water, you place X between magnesium and copper, then narrow the position by comparing the speed of fizzing against zinc or iron. The full reaction equations are on the reactions of metals page.

Displacement reactions

A more reactive metal displaces a less reactive metal from a solution of its salt. The classic:

Zn + CuSO4 → ZnSO4 + Cu

Observations earn their own marks: the blue colour of the solution fades, and a red-brown deposit of copper forms on the zinc. Run the reverse (copper in zinc sulfate) and the answer is “no reaction”, which is worth the mark on its own.

Displacement also works with metal oxides at higher temperature. Magnesium heated with copper(II) oxide: Mg + CuO → MgO + Cu, a vigorous, glowing reaction because magnesium is far above copper.

(Supplement) Displacement is redox. Zinc atoms lose electrons (oxidation): Zn → Zn2+ + 2e−. Copper ions gain them (reduction): Cu2+ + 2e− → Cu. The ionic equation Zn + Cu2+ → Zn2+ + Cu is a standard Extended mark, and “the more reactive metal loses electrons more readily” is the Extended-level definition of the whole series.

Using the series under exam conditions

Three question types cover nearly every appearance:

1. Predict: will metal A displace metal B from solution? Check positions; if A is higher, write the equation; if not, write “no reaction.”
2. Deduce: given a results table of which metal displaced which, rebuild the order. Work pairwise: each “reaction occurred” line means the added metal is higher.
3. Justify extraction: link position relative to carbon to the method, with cost as the tiebreaker (electrolysis is expensive, so it is used only above carbon).

Worked exam question

Three metals, P, Q and R, were each added to solutions of the other two metals’ sulfates. P displaced both Q and R. R displaced neither. (a) Place the metals in order of reactivity, most reactive first. [1] (b) Q is added to dilute sulfuric acid and slow bubbling is seen. R does not react with the acid. Suggest identities for Q and R from: copper, iron, magnesium. [2] (c) Write the equation for iron displacing copper from copper(II) sulfate solution. [2]

Model answer: (a) P > Q > R (1). (b) Q is iron, because it reacts slowly with dilute acid and is above hydrogen but not highly reactive (1); R is copper, because it is below hydrogen and shows no reaction with dilute acid (1). (c) Fe + CuSO4 → FeSO4 + Cu: formulae (1), balanced as written (1).

Mark-by-mark: (a) follows directly from the displacement logic. (b) needs the hydrogen-marker reasoning, not just the names; “slow bubbling” pins iron rather than magnesium. (c) iron forms iron(II) sulfate here; FeSO4, not Fe2(SO4)3, and Cu2SO4 is a formula error that voids both marks.

The mistakes that cost marks

1. A misordered series. Aluminium above magnesium and zinc above carbon are the two most common transpositions. Drill the list cold: K, Na, Ca, Mg, Al, C, Zn, Fe, H, Cu, Ag, Au.
2. Ignoring the markers. Carbon decides extraction; hydrogen decides acid reactions. Answers that quote the series but never use the marker miss the reasoning mark.
3. Inventing reactions that cannot happen. Copper added to magnesium sulfate: no reaction. Writing products anyway is a guaranteed lost mark; “no reaction” is a valid answer.
4. Wrong iron salt in displacement equations. Displacement from copper(II) sulfate produces iron(II) sulfate, FeSO4. Writing the iron(III) compound is a recurring error.

How examiners want it phrased

Student wording	Mark-scheme wording
”Zinc is stronger than copper"	"Zinc is more reactive than copper, so it displaces copper from copper(II) sulfate solution"
"The blue stuff disappears"	"The blue colour of the solution fades and a red-brown deposit of copper forms"
"Copper doesn’t do anything with acid"	"Copper is below hydrogen in the reactivity series, so it does not react with dilute acids"
"Reactive metals like reacting"	"More reactive metals form positive ions more readily / lose electrons more easily”

Learn the list, then practise the three question types until each takes under a minute. If you can recite the series but freeze when a results table appears, that is a technique gap a free trial lesson can close in one sitting.

Test yourself

Recite K, Na, Ca, Mg, Al, C, Zn, Fe, H, Cu, Ag, Au first, then answer and check.

Q1 (2 marks). Magnesium powder is added to copper(II) sulfate solution. State two observations.

Show answer

• the blue colour of the solution fades [1] • a red-brown deposit of copper forms (the mixture also becomes warm, so the reaction is exothermic) [1]

Q2 (3 marks). Predict whether a reaction occurs in each case, writing an equation where it does: (a) silver added to iron(II) sulfate solution; (b) magnesium added to zinc sulfate solution.

Show answer

• (a) no reaction, because silver is less reactive than iron [1] • (b) reaction occurs, because magnesium is more reactive than zinc [1] • Mg + ZnSO4 → MgSO4 + Zn [1]

Q3 (2 marks). (Extended) Write the ionic equation for magnesium displacing copper from copper(II) sulfate solution, and state which species is oxidised.

Show answer

• Mg + Cu2+ → Mg2+ + Cu (sulfate ions are spectators) [1] • magnesium is oxidised: its atoms lose two electrons: Mg → Mg2+ + 2e− [1]