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Chemical Properties of Metals and the Reactivity Series

Metals do not all react the same way with oxygen, water or acid — and exactly how vigorously each one reacts is what lets us rank them from most to least reactive: the reactivity series.

In this lesson you will

  • Write word and balanced chemical equations for a metal reacting with oxygen, water and dilute acid.
  • Explain what an amphoteric oxide is, using aluminium oxide as the example.
  • Predict whether a metal will react with cold water, hot water, steam, or not at all, from its position in the reactivity series.
  • Use a displacement reaction (metal + salt solution) to decide which of two metals is more reactive.
  • Recall the reactivity series in order and use it to predict acid and displacement reactions for an unfamiliar metal.

Metals and oxygen

Almost every metal combines with oxygen to form a metal oxide: Metal + Oxygen → Metal oxide. Most metal oxides are basic, but aluminium oxide and zinc oxide are amphoteric — they react with both acids and bases to give a salt and water. Not every metal reacts at the same speed: potassium and sodium are so reactive they must be stored under kerosene to keep them away from air; magnesium, aluminium, zinc and lead develop a thin protective oxide layer at room temperature that stops further reaction (this is also the basis of anodising, which thickens that layer on purpose); silver and gold barely react with oxygen even when heated.

Metals and water

Metal + Water → Metal oxide + Hydrogen, and if the oxide dissolves, Metal oxide + Water → Metal hydroxide. Potassium and sodium react so violently with cold water that the heat evolved sets the hydrogen alight. Calcium reacts more gently and floats, held up by hydrogen bubbles. Magnesium does not react with cold water but does with hot water. Aluminium, iron and zinc react with neither cold nor hot water, but do react with steam to give the metal oxide and hydrogen. Lead, copper, silver and gold do not react with water at all.

Metals and dilute acids

Metal + Dilute acid → Salt + Hydrogen — but again, not at the same rate. With dilute hydrochloric acid, magnesium reacts fastest, followed by aluminium, then zinc, then iron; copper does not react at all. Nitric acid is a special case: it is such a strong oxidising agent that it usually oxidises the hydrogen produced into water instead of releasing it as gas — except when very dilute nitric acid reacts with magnesium or manganese, which still evolve hydrogen. Aqua regia, a 3:1 mixture of concentrated hydrochloric and nitric acids, can dissolve gold and platinum even though neither acid can do so alone.

Displacing one metal with another

A more reactive metal can push a less reactive metal out of its salt solution: Metal A + Salt solution of B → Salt solution of A + Metal B, provided A is more reactive than B. An iron nail placed in copper sulphate solution comes out coated in copper; a copper wire placed in iron sulphate solution shows no change — iron is more reactive than copper.

The reactivity series

Put the oxygen, water, acid and displacement evidence together and one consistent ranking falls out — the reactivity series, from most to least reactive:

K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au

Hydrogen is included, even though it is not a metal, as the dividing line: every metal above it displaces hydrogen from a dilute acid; every metal below it does not.

Key terms

Amphoteric oxide
A metal oxide that reacts with both acids and bases to produce a salt and water — aluminium oxide and zinc oxide are the two NCERT examples.
Reactivity series
A list of common metals arranged in order of decreasing chemical reactivity, built from displacement and other reaction evidence.
Displacement reaction
A reaction in which a more reactive metal pushes a less reactive metal out of its salt solution, taking its place.
Aqua regia
A freshly prepared 3:1 mixture of concentrated hydrochloric and nitric acids that can dissolve gold and platinum, though neither acid can alone.

Key relationships

  • Metal + Oxygen → Metal oxide (most metal oxides are basic).
  • Amphoteric oxides (Al2O3, ZnO) react with acids AND bases to give a salt and water.
  • Metal + Water → Metal oxide + Hydrogen; Metal oxide + Water → Metal hydroxide (when the oxide is soluble).
  • Metal + Dilute acid → Salt + Hydrogen (except with nitric acid, which usually does not release H2).
  • Metal A + Salt solution of B → Salt solution of A + Metal B, only when A is more reactive than B.
  • Reactivity order observed with dilute HCl: Mg > Al > Zn > Fe; copper does not react at all.
  • Full reactivity series (most to least reactive): K, Na, Ca, Mg, Al, Zn, Fe, Pb, [Hydrogen], Cu, Hg, Ag, Au.

Formulae

Metal + oxygen

2Cu + O2 → 2CuO

  • Cu = copper
  • CuO = copper(II) oxide, black

Amphoteric oxide with acid and base

Al2O3 + 6HCl → 2AlCl3 + 3H2O and Al2O3 + 2NaOH → 2NaAlO2 + H2O

  • NaAlO2 = sodium aluminate

Reactive metal + cold water

2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) + heat

Metal + steam

3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)

Metal + dilute acid

Metal + Dilute acid → Salt + Hydrogen

Displacement from a salt solution

Metal A + Salt solution of B → Salt solution of A + Metal B

Only happens when A is MORE reactive than B.

Activities

Activity 3.9 — Burning metals in air (safe virtual demonstration)

What you do: A teacher burns small samples of several metals in a flame using tongs and eye protection, and the ash/product is collected and compared.

What you see: Magnesium burns with a dazzling white flame; sodium and potassium are so reactive they are never burnt this way (kept in kerosene instead); iron filings burn vigorously in a flame though a solid iron block does not; copper does not burn but its hot surface blackens; silver and gold barely react even at high temperature.

What it shows: All metals react with oxygen, but at very different rates — that rate is the first piece of reactivity-series evidence.

Activity 3.10 — Metals meeting cold water, hot water and steam (safe virtual demonstration)

What you do: Small pieces of each metal are tried in cold water, then (if unreacted) hot water, then (if still unreacted) passed through steam, always with teacher supervision.

What you see: Potassium and sodium react so violently with cold water that the hydrogen produced catches fire; calcium reacts steadily and floats; magnesium is unreactive cold but reacts with hot water; aluminium, iron and zinc react only with steam; lead, copper, silver and gold do not react with water at all.

What it shows: Reactivity with water divides the metals into clear bands — more reactivity-series evidence, independent of the oxygen test.

Activity 3.11 — Metals meeting dilute hydrochloric acid

What you do: Clean metal samples (excluding sodium and potassium, which are far too dangerous even with cold water) are dropped into dilute HCl with a thermometer in each tube; the rate of bubbling and the temperature rise are compared.

What you see: Magnesium fizzes fastest and heats up the most; the order Mg > Al > Zn > Fe follows from the bubble rate; copper produces no bubbles and no temperature change at all.

What it shows: Reaction with acid gives a third, independent line of reactivity evidence — and confirms copper sits below hydrogen in the series.

Activity 3.12 — Which metal displaces which? (iron nail and copper wire)

What you do: A copper wire is placed in iron(II) sulphate solution; an iron nail is placed in copper(II) sulphate solution, in two separate test tubes, and left for 20 minutes.

What you see: The iron nail in copper sulphate develops a reddish-brown copper coating and the blue colour of the solution fades; the copper wire in iron sulphate shows no change at all.

What it shows: Iron displaces copper from its salt solution, but copper cannot displace iron — proof that iron is more reactive than copper, the clearest and most direct reactivity-series evidence of all.

What you should be able to do

Recognise

  • An amphoteric oxide from a description of it reacting with both acid and base.
  • A displacement reaction from a metal + salt-solution word equation, and which metal is more reactive.
  • Why a particular metal reacts with cold water, hot water only, steam only, or not at all.

Explain

  • Why sodium and potassium are stored under kerosene.
  • Why nitric acid does not usually produce hydrogen gas with a metal.
  • Why copper does not react with dilute hydrochloric acid.

State

  • The reactivity series, in order, from potassium to gold.
  • The general word equations: metal+oxygen, metal+water, metal+dilute acid, metal+salt solution.

NCERT alignment

This topic corresponds to NCERT Class 10 Science, Chapter “Metals and Non-metals”, sections 3.2, 3.2.1, 3.2.2, 3.2.3, 3.2.4, 3.2.5; activities 3.9, 3.10, 3.11, 3.12. Explanations, visuals and worked material here are original.

Quick revision

  • Metal + Oxygen → Metal oxide (most basic; Al2O3 and ZnO are amphoteric).
  • Metal + Water → Metal oxide + Hydrogen; only K, Na, Ca react with cold water; Mg needs hot water; Al/Fe/Zn need steam; Pb/Cu/Ag/Au never react.
  • Metal + Dilute acid → Salt + Hydrogen; observed order Mg > Al > Zn > Fe > (no reaction) Cu; HNO3 is an exception (usually no H2).
  • A more reactive metal displaces a less reactive one from its salt solution — the clearest reactivity evidence.
  • Reactivity series: K, Na, Ca, Mg, Al, Zn, Fe, Pb, [H], Cu, Hg, Ag, Au — most to least reactive.
  • Aqua regia (conc. HCl : conc. HNO3, 3:1) dissolves gold and platinum, which no acid can do alone.