Reactivity Series And Corrosion Of Metals

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Lesson notes

Reactivity Series

The reactivity series lists metals in order of their reactivity based on reactions with water and acids.
Non-metals carbon and hydrogen are included for extraction and acid reactions.
Order (most to least reactive): Potassium > Sodium > Calcium > Magnesium > Aluminium > Carbon > Zinc > Iron > Hydrogen > Copper > Silver > Gold.
Mnemonic: 'Please send cats, monkeys and cute zebras into hot countries signed Gordon'.

Reactions with Water and Steam

Potassium, sodium, and calcium react with cold water to produce metal hydroxide and hydrogen gas.
Example: 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g).
Magnesium reacts with steam to produce magnesium oxide and hydrogen: Mg(s) + H₂O(g) → MgO(s) + H₂(g).
Reactivity with water decreases down the series: potassium reacts violently, sodium quickly, calcium less strongly.

Reactions with Dilute Hydrochloric Acid

Metals above hydrogen in the series react with dilute HCl to form a salt and hydrogen gas.
Example: Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g).
The more reactive the metal, the more vigorous the reaction.
Metals below hydrogen (copper, silver, gold) do not react with dilute HCl.

Displacement Reactions

A more reactive metal can displace a less reactive metal from a solution of its salt.
Example: Mg(s) + CuSO₄(aq) → MgSO₄(aq) + Cu(s); blue colour fades as copper deposits.
Displacement occurs because more reactive metals lose electrons more readily (are better reducing agents).
Experimental displacement data can be used to deduce the relative order of reactivity.

Displacement of copper by magnesium

Explaining Reactivity (Extended)

Reactivity depends on the tendency of a metal atom to lose electrons and form positive ions.
Metals high in the series lose electrons easily and are strong reducing agents.
In displacement, the less reactive metal ion gains electrons (is reduced); the more reactive metal loses electrons (is oxidised).

Rusting of Iron

Rusting is the corrosion of iron requiring both oxygen and water.
Rust is hydrated iron(III) oxide, a reddish-brown compound.
Equation: iron + water + oxygen → hydrated iron(III) oxide.
Only iron or steel rusts; other metals corrode.
Investigating rusting: nail in air+water rusts; nail in boiled water with oil (no air) does not; nail with calcium chloride (no water) does not.

Requirements for rusting

Rust Prevention Methods

Barrier methods (grease, oil, paint, plastic) prevent contact with water and oxygen.
If the barrier is scratched, iron is exposed and rusting occurs.
Sacrificial protection uses a more reactive metal (e.g., zinc) attached to iron; the more reactive metal corrodes instead.
Zinc bars on steel ships: Zn → Zn²⁺ + 2e⁻; zinc oxidises, iron is protected.
Galvanising coats iron with zinc; acts as barrier and provides sacrificial protection if scratched.

Zinc bars on steel ship hulls

Choosing a Protective Metal (Extended)

A metal above iron in the reactivity series is suitable for sacrificial protection (e.g., zinc, magnesium).
A metal below iron (e.g., copper) is not suitable; iron would corrode instead.

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Practice questions

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1.Which of the following is the correct order of reactivity for the metals potassium, sodium, calcium, magnesium, aluminium, zinc, iron, copper, silver, gold?
Easy
- APotassium > Sodium > Calcium > Magnesium > Aluminium > Zinc > Iron > Copper > Silver > Gold
- BGold > Silver > Copper > Iron > Zinc > Aluminium > Magnesium > Calcium > Sodium > Potassium
- CPotassium > Sodium > Magnesium > Calcium > Aluminium > Zinc > Iron > Copper > Silver > Gold
- DSodium > Potassium > Calcium > Magnesium > Aluminium > Zinc > Iron > Copper > Silver > Gold
2.State the two conditions necessary for rusting to occur.
Easy
3.Iron can rust in the presence of water alone, without oxygen.
Easy
True or false?
4.Complete the sentence: In the reactivity series, carbon is placed between aluminium and zinc because it is used to extract metals from their oxides.
Medium
In the reactivity series, carbon is placed between ____ and ____ because it is used to extract metals from their oxides.
5.Match each metal with its reaction with cold water.
Medium
- Potassium
- Sodium
- Calcium
- Magnesium
- Reacts violently
- Reacts quickly
- Reacts less strongly
- Does not react with cold water
6.Write the word equation for the reaction of magnesium with steam.
Medium
7.In an experiment to determine the reactivity of a metal, a student measures the temperature change when the metal reacts with dilute hydrochloric acid. The temperature rises from 20.0°C to 35.0°C. What is the temperature change in °C?
Easy
- A15
- B17
- C14
- D16
8.Which of the following metals will displace copper from copper(II) sulfate solution?
Easy
- ASilver
- BGold
- CZinc
- DCopper

Flashcards

What is the order of the reactivity series from most reactive to least reactive?

Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Hydrogen, Copper, Silver, Gold.

What is the mnemonic to remember the reactivity series?

Please send cats, monkeys and cute zebras into hot countries signed Gordon.

Which metals react with cold water?

Potassium, sodium, and calcium react with cold water to form a metal hydroxide and hydrogen gas.

Write the balanced equation for the reaction of potassium with water.

2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)

How does magnesium react with steam?

Magnesium reacts with steam to form magnesium oxide and hydrogen gas: Mg (s) + H2O (g) → MgO (s) + H2 (g).

Which metals react with dilute hydrochloric acid?

Metals above hydrogen in the reactivity series, such as magnesium, zinc, and iron, react with dilute hydrochloric acid to produce a salt and hydrogen.

Write the equation for the reaction of zinc with dilute hydrochloric acid.

Zn (s) + 2HCl (aq) → ZnCl2 (aq) + H2 (g)

Why do copper, silver, and gold not react with dilute hydrochloric acid?

They are below hydrogen in the reactivity series, so they do not displace hydrogen from acids.

How can the order of reactivity be deduced experimentally?

By observing the vigour of reactions with water or dilute hydrochloric acid; the more vigorous the reaction, the more reactive the metal.

What happens when magnesium is added to copper(II) sulfate solution?

Magnesium displaces copper: Mg (s) + CuSO4 (aq) → MgSO4 (aq) + Cu (s). The blue colour fades and copper metal forms.

What is a displacement reaction between a metal and a salt solution?

A more reactive metal displaces a less reactive metal from its salt solution.

What is rusting?

Rusting is the reaction of iron with water and oxygen to form hydrated iron(III) oxide, a reddish-brown compound.

What conditions are necessary for rusting to occur?

Both oxygen and water must be present for iron to rust.

How can you investigate the conditions required for rusting?

Use three test tubes: one with iron nail exposed to air and water, one with boiled water and oil to exclude air, and one with calcium chloride to absorb moisture. Only the nail in the first tube rusts.

What are barrier methods to prevent rust?

Coating iron with grease, oil, paint, or plastic to prevent contact with water and oxygen.

What is sacrificial protection?

Attaching a more reactive metal (e.g., zinc) to iron; the more reactive metal corrodes first, protecting the iron.

Explain why zinc is used for sacrificial protection of steel ships.

Zinc is more reactive than iron, so it loses electrons and oxidises preferentially, preventing the iron from rusting.

What is galvanising?

Coating iron with a layer of zinc, which provides both barrier protection and sacrificial protection if the coating is scratched.

Why is a metal below iron in the reactivity series not suitable for sacrificial protection?

It would not be oxidised instead of iron; iron would still rust because the less reactive metal cannot protect it.

What is the product of rusting?

Hydrated iron(III) oxide (Fe2O3·xH2O).

What is the difference between rusting and corrosion?

Rusting refers specifically to the corrosion of iron or steel; corrosion is the general term for the breakdown of any metal.

What is the word equation for rusting?

iron + water + oxygen → hydrated iron(III) oxide

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