Reactivity series -- the order, K down to Au
Most reactive first: potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold.
Carbon and hydrogen are non-metals, included as reference lines: metals below carbon can be extracted by reduction with carbon (C9.6), and metals above hydrogen react with dilute acids. Mnemonic: Poor Sailors Cannot Make A Canoe Zigzag In Heavy Currents At Gale-force.
Cold water and steam -- who reacts with what
Potassium, sodium and calcium react with cold water to give a metal hydroxide plus hydrogen, vigour falling K > Na > Ca:
Magnesium shows no noticeable reaction with cold water, but burns in steam:
Higher in the series means atoms lose electrons more readily -- cold water suffices for K, Na and Ca; magnesium needs steam.
Dilute hydrochloric acid -- the hydrogen line
Magnesium, zinc and iron react with dilute hydrochloric acid to give hydrogen plus MgCl, ZnCl or FeCl, fizzing least vigorously in that order. Copper, silver and gold give no reaction: they sit below hydrogen.
(Extended) The same property -- tendency to form positive ions -- drives displacement: a higher metal loses electrons more readily, so it displaces a lower metal''s aqueous ions.
Drawn from real examiner reports.
Magnesium: steam, not cold water
Magnesium shows essentially no reaction with COLD water (at most an extremely slow one). It is with STEAM -- water in the gas state -- that magnesium reacts vigorously, glowing brightly and leaving white magnesium oxide. Writing that magnesium "reacts vigorously with cold water" is a factual error, not just an imprecision.
Below hydrogen means no acid reaction
Copper, silver and gold do not react with dilute hydrochloric acid at all -- no bubbles, no warming, no salt. They lie BELOW hydrogen in the series, so their atoms will not lose electrons to the acid''s hydrogen ions. Writing an equation such as Cu + 2HCl gives CuCl + H describes a reaction that does not happen.
(Extended) "More reactive" is not an explanation
"Magnesium displaces copper because magnesium is more reactive" restates the observation. The Extended mark scheme wants the mechanism: the more reactive metal has a GREATER TENDENCY TO FORM POSITIVE IONS -- its atoms lose electrons (are oxidised) more readily, and those electrons are gained by the less reactive metal''s ions.
(Extended) Displacement only runs downhill
The ADDED metal must be higher in the series than the metal already in solution. Magnesium added to aqueous copper(II) sulfate displaces copper; silver added to aqueous magnesium sulfate does nothing at all. Reversing the direction -- or writing "a reaction occurs" whenever two different metals meet -- loses the mark.
Flagged Jun 2022 P11 Q24; Nov 2023 P43 Q2e, P13 Q24
Reactivity order ≠ table row order
Reactivity does not necessarily increase as you read down a results table -- the order metals are printed in is not their reactivity order. Rank them yourself from the data actually given: fastest fizzing, largest gas volume or most displacements caused = most reactive. Quoting the table order back is the flagged error.
Flagged Jun 2022 P11 Q24; Nov 2023 P43 Q2e, P13 Q24
Carbon sits above zinc, iron and copper
Carbon is a reference line inside the series, not an afterthought at the bottom. It is placed between aluminium and zinc, so it is MORE reactive than zinc, iron and copper -- which is exactly why carbon can reduce those metals out of their compounds. Candidates asked to explain this often omit that carbon is the more reactive one.
Flagged Jun 2022 P11 Q24; Nov 2023 P43 Q2e, P13 Q24
"It reacts" is not a description
"It reacts" or "bubbles form" earns little credit. A described reaction names the gas released (hydrogen), the observations -- fizzing, and for K and Na floating, melting into a ball, moving across the surface, possibly igniting -- and the product: a hydroxide from cold water, an oxide from steam, a chloride from the acid.
Flagged Jun 2022 P32 Q5a
Deduce the order in four steps
Answer the command word actually asked
"State" the order = the list. "Describe" a reaction = observations plus products. "Explain" = link it to the metal''s position in the series (at Extended, to the tendency to form positive ions). A true but off-question answer scores nothing; match the points to the tariff.
Balance the equation before you move on
Write the correct formulae first, then balance -- never change a formula to make the numbers work. Hydrogen leaves as H, not H. Two of the three acid equations here need a 2 in front of HCl, and sodium with cold water needs a 2 on Na, HO and NaOH.
(Extended) Ionic equations: balance the charge
An ionic equation shows only the species that change, so spectator ions (sulfate, nitrate) are left out. Then check BOTH balances -- atoms AND total charge. Silver ions carry only 1+, so displacing silver with a 2+ metal needs a 2 on each side: Zn + 2Ag gives Zn + 2Ag.
Cambridge 0654 spec reference: Section C9 "Metals", sub-topic C9.4 "Reactivity series". Core: state the reactivity series order (potassium to gold); describe the reactions, if any, of potassium/sodium/calcium with cold water, magnesium with steam, and magnesium/zinc/iron/copper/silver/gold with dilute hydrochloric acid, explaining each in terms of the metal's position in the series; deduce an order of reactivity from given experimental results. Supplement (Extended): describe the relative reactivities of metals in terms of their tendency to form positive ions, using displacement reactions (if any) with the aqueous ions of magnesium, zinc, iron, copper and silver.
| Term | Mark-scheme-precise meaning |
|---|---|
| Reactivity series | A list of metals (plus the non-metal reference points carbon and hydrogen) arranged in order of decreasing chemical reactivity |
| More reactive (metal) (Extended) | Has a greater tendency to form positive ions -- i.e. its atoms lose electrons (are oxidised) more readily |
| Displacement reaction (Extended) | A more reactive metal takes the place of a less reactive metal in an aqueous solution of its ions, because it has a greater tendency to lose electrons and form positive ions |
The 0654 reactivity series (Core), most to least reactive:
potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold. Carbon and hydrogen are included only as reference points (they are non-metals): carbon marks the divide used for extraction methods (C9.6); hydrogen marks the divide for reaction with dilute acids.
Define the term "reactivity series".
Write the balanced symbol equation, including state symbols, for magnesium reacting with dilute hydrochloric acid. (2 marks)
