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5.1 The Reactivity Series

GCSE Chemistry · AQA · Chapter 5: Chemical Changes

A free GCSE Chemistry lesson for AQA (8462) from OBA School: how metals react with oxygen, water, steam and dilute acids, and how we put them in order of reactivity. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

  • Describe the reactions of metals with oxygen, water, steam and dilute acids, and write balanced equations for them
  • Recall the reactivity series, including the positions of carbon and hydrogen
  • Link the reactivity of a metal to its tendency to form positive ions
  • Use experimental results to put metals in order of reactivity
  • Use reactivity to explain how metals are used and why aluminium resists corrosion, and predict how an unfamiliar metal reacts

Key words

  • Reactivity series: A list of metals in order of how vigorously they react, most reactive at the top.
  • Oxidation: Gain of oxygen by a substance. (In Higher tier, also loss of electrons.)
  • Metal oxide: The compound formed when a metal reacts with oxygen, e.g. magnesium oxide, MgO.
  • Metal hydroxide: The compound formed (with hydrogen) when a very reactive metal reacts with water, e.g. NaOH.
  • Positive ion: An atom that has lost one or more electrons, e.g. Na⁺, Mg²⁺.
  • Reduction: Loss of oxygen by a substance, e.g. a metal oxide losing oxygen to give the metal.
  • Effervescence: Fizzing: bubbles of gas given off during a reaction.

Metals and oxygen

Most metals react with oxygen to form a metal oxide. The metal gains oxygen, so it is oxidised. Reactive metals tarnish quickly in air; magnesium burns with a bright white flame; copper only forms a black oxide layer when heated strongly. Gold does not react at all.

magnesium + oxygen → magnesium oxide 2Mg(s) + O₂(g) → 2MgO(s)

copper + oxygen → copper oxide 2Cu(s) + O₂(g) → 2CuO(s)

sodium + oxygen → sodium oxide 4Na(s) + O₂(g) → 2Na₂O(s)

Key fact: Oxidation is the gain of oxygen. Reduction is the loss of oxygen. You will meet the electron definitions in section 5.2.

Over millions of years, many metals in the Earth’s crust have combined with oxygen, so they are found as oxides in rocks. To get the metal back, the oxygen must be removed: the oxide must be reduced. How hard that is depends on the metal’s place in the reactivity series (section 5.3).

Metals with water and steam

The Group 1 metals and calcium react with cold water to give a metal hydroxide and hydrogen. The hydroxide dissolves to make an alkaline solution.

sodium + water → sodium hydroxide + hydrogen 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

calcium + water → calcium hydroxide + hydrogen Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)

Magnesium reacts only very slowly with cold water, but quickly with steam. With steam a metal forms its oxide (not hydroxide) and hydrogen. Zinc and iron also react with steam, but more slowly. Copper does not react with water or steam.

magnesium + steam → magnesium oxide + hydrogen Mg(s) + H₂O(g) → MgO(s) + H₂(g)

Metals with dilute acids

Metals above hydrogen in the series react with dilute hydrochloric or sulfuric acid to give a salt and hydrogen. The faster the fizzing, the more reactive the metal. Potassium and sodium react dangerously, so they are never added to acid in school. Metals below hydrogen (copper, silver, gold) do not react with dilute acids.

  • potassium, sodium, lithium; Cold water fizz quickly; float and move about (K ignites); Dilute hydrochloric acid violent – too dangerous to try
  • calcium; Cold water fizzes steadily; Dilute hydrochloric acid very vigorous fizzing
  • magnesium; Cold water a few bubbles over several days; Dilute hydrochloric acid fast fizzing; gets warm
  • zinc; Cold water no visible reaction; Dilute hydrochloric acid steady fizzing
  • iron; Cold water rusts very slowly (needs air too); Dilute hydrochloric acid slow fizzing
  • copper; Cold water no reaction; Dilute hydrochloric acid no reaction

zinc + hydrochloric acid → zinc chloride + hydrogen Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

Key fact: Test for hydrogen: collect the gas in a test tube and hold a lighted splint at the mouth. Hydrogen burns with a squeaky pop. The hydrogen reacts with oxygen in the air to make water.

Aluminium: a special case

Aluminium is quite high in the series, but an aluminium ladder or window frame can last for decades outdoors. As soon as fresh aluminium meets air, a very thin, tough layer of aluminium oxide forms on its surface. This layer sticks firmly and stops air and water reaching the metal underneath, so aluminium seems much less reactive than it really is.

If the oxide layer is scratched off (or removed with a chemical), the aluminium underneath reacts as expected – for example, it fizzes steadily in dilute hydrochloric acid.

Reactivity explains how we use metals

  • Gold and platinum keep their shine for centuries, so they are used for rings and electrical contacts.; Explained by reactivity They are at the bottom of the series and do not react with air, water or dilute acids.
  • Copper is used for hot-water pipes.; Explained by reactivity Copper is below hydrogen, so it does not react with water, even when hot.
  • Lithium, sodium and potassium are stored under oil.; Explained by reactivity They are so reactive that they react with oxygen and water vapour in the air.
  • Aluminium is used for outdoor ladders and greenhouse frames.; Explained by reactivity Its protective oxide layer stops it corroding.

Worked example: predicting the behaviour of an unfamiliar metal

Manganese lies between aluminium and zinc in the reactivity series. Predict how it reacts with dilute sulfuric acid.
It is above hydrogen, so it will react to give a salt and hydrogen: manganese + sulfuric acid → manganese sulfate + hydrogen.
It is below magnesium but above zinc, so it should fizz faster than zinc but more slowly than magnesium.

Answer: steady fizzing; manganese sulfate and hydrogen form

The reactivity series and positive ions

When metals react, their atoms lose electrons to form positive ions. The more easily a metal forms positive ions, the more reactive it is. Potassium loses its one outer electron very easily, so it is at the top. Copper forms ions much less easily, so it is near the bottom.

Exam tip: Learn the AQA order: potassium, sodium, lithium, calcium, magnesium, carbon, zinc, iron, hydrogen, copper. Aluminium sits between magnesium and carbon; silver and gold are below copper.

Ordering metals from results

A student added 1 g of four metals, W, X, Y and Z, to separate 50 cm³ portions of the same dilute acid at the same temperature. She collected the hydrogen for 2 minutes.

Worked example: using the results

More gas in the same time means a faster reaction, so a more reactive metal.
Order: W (62 cm³) > Y (25 cm³) > X (3 cm³) > Z (0 cm³).
Z gives no gas, so Z is below hydrogen in the series (for example copper).
Mean rate for W = 62 ÷ 120 = 0.52 cm³/s (2 s.f.).

Answer: most reactive W, Y, X, Z least reactive

For a fair test, keep the same mass and surface area of metal, the same acid concentration and volume, and the same temperature.

Common mistakes

  • Saying a metal + water always gives a hydroxide. With steam, the product is the metal oxide.
  • Forgetting carbon and hydrogen in the series – they are non-metals but are used for comparison.
  • Writing “copper reacts slowly with acid”. Copper is below hydrogen, so it does not react with dilute acids.
  • Writing hydrogen as H in equations. Hydrogen gas is diatomic: H₂.
  • Thinking aluminium is unreactive because it does not corrode. It is protected by a thin oxide layer; the metal itself is quite reactive.

Revision questions

Try these, then check your answers below each one.

Question 1. Which list puts the metals in order of reactivity, most reactive first? (Choose from: potassium, calcium, magnesium, zinc, copper, calcium, potassium, zinc, magnesium, copper, potassium, magnesium, calcium, copper, zinc, copper, zinc, magnesium, calcium, potassium.)

Answer: potassium, calcium, magnesium, zinc, copper

Working: The reactivity series runs potassium > sodium > lithium > calcium > magnesium > (carbon) > zinc > iron > (hydrogen) > copper.

Question 2. True or false? Copper reacts slowly with dilute hydrochloric acid to give hydrogen.

Answer: False

Working: Copper is below hydrogen in the reactivity series, so it does not react with dilute acids. The statement is false.

Question 3. Name the gas given off when calcium reacts with water.

Answer: hydrogen

Working: calcium + water → calcium hydroxide + hydrogen. Ca + 2H₂O → Ca(OH)₂ + H₂

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