The Reactivity Series
The order of metals and how they react with oxygen, water and acids
The Reactivity Series
The reactivity series is a list of metals arranged in order of their reactivity, from most reactive at the top to least reactive at the bottom. Carbon and hydrogen are included as reference points for extraction methods.
Oxidation and Reduction (in terms of oxygen)
Reduction is the loss of oxygen.
A helpful way to remember: Oxidation = Oxygen gained, Reduction = Removal of oxygen.
H At Higher tier, oxidation and reduction are also defined in terms of electron transfer: OIL RIG – Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons). See C5.2 for more detail.
When a metal reacts with oxygen, the metal is oxidised (it gains oxygen). If a metal oxide loses its oxygen, the metal oxide is reduced.
Magnesium is oxidised – it gains oxygen.
Metals Reacting with Oxygen
When metals react with oxygen, they form metal oxides. The more reactive the metal, the more vigorously it reacts.
| Metal | Word Equation | Observations |
|---|---|---|
| Magnesium | magnesium + oxygen → magnesium oxide | Burns with a brilliant white flame; white powder (ash) formed |
| Iron | iron + oxygen → iron oxide | Glows orange/yellow; forms a dark reddish-brown solid (iron oxide) |
| Copper | copper + oxygen → copper oxide | Surface slowly turns black (copper oxide layer forms) |
Balanced Symbol Equations
Metals Reacting with Water
Reactive metals react with water to produce a metal hydroxide and hydrogen gas.
| Metal | Reaction with Water | Observations |
|---|---|---|
| Potassium | Very vigorous | Fizzes rapidly, moves on surface, lilac flame, melts into a ball |
| Sodium | Vigorous | Fizzes, moves on surface, melts into a silvery ball, may ignite |
| Lithium | Steady | Fizzes steadily, moves on surface, gradually dissolves |
| Calcium | Moderate | Fizzes, sinks, water turns milky/cloudy |
| Magnesium | Very slow with cold water | Very few bubbles with cold water; reacts well with steam |
| Iron | Does not react with water | No reaction (but does react very slowly with steam) |
| Copper | No reaction | No reaction at all |
Example Balanced Equations
Magnesium reacts with steam (not cold water):
Metals Reacting with Acids
Metals above hydrogen in the reactivity series react with dilute acids to produce a salt and hydrogen gas.
The name of the salt depends on the acid used:
- Hydrochloric acid → metal chloride
- Sulfuric acid → metal sulfate
- Nitric acid → metal nitrate (but nitric acid reactions are more complex)
| Metal | With HCl | Observations |
|---|---|---|
| Magnesium | magnesium + hydrochloric acid → magnesium chloride + hydrogen | Vigorous fizzing, metal dissolves quickly, solution warms up |
| Zinc | zinc + hydrochloric acid → zinc chloride + hydrogen | Steady fizzing, metal dissolves slowly |
| Iron | iron + hydrochloric acid → iron(II) chloride + hydrogen | Slow fizzing, very slow dissolving, solution turns pale green |
| Copper | No reaction | No fizzing, no change – copper is below hydrogen |
Balanced Symbol Equations
Uses of Metals and Reactivity
The reactivity of a metal determines what it can be used for:
- Gold and platinum are used for jewellery because they are unreactive – they do not tarnish or corrode.
- Copper is used for water pipes and electrical wiring because it is unreactive with water and is a good conductor.
- Iron/steel is used in construction but must be painted or galvanised to prevent rusting (it reacts slowly with oxygen and water).
- Aluminium forms a tough oxide layer that protects it from further corrosion, making it useful for aircraft and drinks cans.
Method: Place equal-sized pieces of different metals into test tubes containing equal volumes of dilute hydrochloric acid at the same concentration. Observe and record the rate of fizzing.
Control variables:
- Volume and concentration of acid
- Size/mass of metal pieces
- Temperature of acid
Dependent variable: Rate/vigour of reaction (volume of gas produced, or time for metal to dissolve)
Evaluating the investigation: Consider whether the metal pieces were truly the same surface area, whether the temperature was controlled, and whether subjective observations (like “vigorous”) could be made more quantitative by collecting gas in a gas syringe.
Practice Questions
Which of the following metals reacts most vigorously with water?
Potassium is the most reactive metal listed. It reacts violently with water, producing a lilac flame and moving rapidly across the surface.
What is produced when zinc reacts with sulfuric acid?
Metal + sulfuric acid → metal sulfate + hydrogen. So zinc + sulfuric acid → zinc sulfate + hydrogen.
Define the terms oxidation and reduction in terms of oxygen.
Oxidation is the gain of oxygen. [1 mark]
Reduction is the loss of oxygen. [1 mark]
A student adds a piece of magnesium ribbon to dilute hydrochloric acid. Describe what they would observe, write the word equation, and write the balanced symbol equation.
Observation: The magnesium fizzes vigorously / bubbles of gas are produced. The magnesium dissolves and the solution gets warm. [1 mark]
Word equation: magnesium + hydrochloric acid → magnesium chloride + hydrogen [1 mark]
Symbol equation: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) [1 mark]
Which metal does NOT react with dilute hydrochloric acid?
Copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from an acid. No reaction occurs.
Explain why gold is suitable for use in jewellery but iron is not, with reference to the reactivity series.
Gold is at the bottom of the reactivity series, meaning it is very unreactive [1 mark]. It does not react with oxygen or water, so it does not corrode or tarnish [1 mark]. Iron is higher in the reactivity series and reacts with oxygen and water to form rust (iron oxide), so it would corrode and lose its appearance [1 mark].
A student investigates the reactivity of metals by adding pieces of metal to dilute acid and timing how long it takes for the metal to dissolve. Suggest two control variables and explain how the student could improve the validity of their results.
Control variables (any two for 2 marks):
- Volume of acid
- Concentration of acid
- Size/surface area of the metal piece
- Starting temperature of the acid
Improving validity: The student could collect the gas produced in a gas syringe and measure the volume of gas in a given time, rather than subjectively judging the vigour of the reaction [1 mark]. They should also repeat each test at least 3 times and calculate a mean [1 mark].
Write a balanced symbol equation, including state symbols, for the reaction of calcium with water.
[1 mark for correct formula and balancing, 1 mark for correct state symbols]