Reactivity of Metals

This lesson covers the reactivity of metals, a key topic in the AQA GCSE Chemistry specification (4.4.1). You need to understand how metals react with water and acids, explain reactivity in terms of the tendency of a metal to form its positive ion, and use the reactivity series to predict displacement reactions. This knowledge underpins understanding of metal extraction, corrosion, and industrial chemistry.

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The Reactivity Series

The reactivity series is an arrangement of metals in order of their reactivity, from the most reactive to the least reactive. The position of a metal in the reactivity series is determined by how vigorously it reacts with water, dilute acids, and other metal compounds.

Position	Metal	Symbol	Reactivity
1 (most reactive)	Potassium	K	Reacts violently with cold water; stored in oil
2	Sodium	Na	Reacts vigorously with cold water; stored in oil
3	Lithium	Li	Reacts steadily with cold water
4	Calcium	Ca	Reacts with cold water, producing a steady stream of bubbles
5	Magnesium	Mg	Reacts very slowly with cold water but vigorously with steam and dilute acids
6	Aluminium	Al	Appears unreactive due to an oxide layer, but is actually quite reactive
7	Zinc	Zn	Reacts with dilute acids; does not react with cold water
8	Iron	Fe	Reacts slowly with dilute acids; rusts in the presence of water and oxygen
9	Tin	Sn	Reacts very slowly with dilute acids
10	Lead	Pb	Reacts very slowly with dilute acids
11	Hydrogen	H	Not a metal — included as a reference point
12	Copper	Cu	Does not react with water or dilute acids
13	Silver	Ag	Very unreactive
14	Gold	Au	Extremely unreactive
15 (least reactive)	Platinum	Pt	Extremely unreactive

Exam Tip: A common mnemonic for the reactivity series is: Please Stop Letting Careless Monkeys Always Zip Into The London House Cupboard Secretly Grabbing Platinum. Learn it thoroughly — it appears in almost every Chemistry exam paper.

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Reactions of Metals with Water

Metals above hydrogen in the reactivity series react with water (or steam) to produce a metal hydroxide (or metal oxide with steam) and hydrogen gas.

The general word equation is:

metal + water → metal hydroxide + hydrogen

Metal	Observation with cold water	Products
Potassium	Lilac flame, moves rapidly on the surface, may explode	Potassium hydroxide + hydrogen
Sodium	Melts into a shiny ball, moves on surface, may ignite with yellow flame	Sodium hydroxide + hydrogen
Lithium	Fizzes steadily on surface of water	Lithium hydroxide + hydrogen
Calcium	Sinks, steady bubbles of gas produced, water turns milky with universal indicator	Calcium hydroxide + hydrogen
Magnesium	Very slow reaction with cold water; reacts vigorously with steam	Magnesium hydroxide (or magnesium oxide with steam) + hydrogen

Testing for Hydrogen Gas

To confirm that hydrogen gas is produced, collect the gas and apply a burning splint. Hydrogen burns with a squeaky pop.

Exam Tip: When describing reactions of metals with water, always state the observations (what you would see) as well as the products. Examiners award marks for both. For example: "Sodium melts into a shiny ball, moves across the surface of the water, and fizzes as hydrogen gas is produced."

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Reactions of Metals with Dilute Acids

Metals above hydrogen in the reactivity series react with dilute acids (such as hydrochloric acid or sulfuric acid) to produce a salt and hydrogen gas.

The general word equation is:

metal + acid → salt + hydrogen

Metal	Acid	Salt produced	Observation
Magnesium	Hydrochloric acid	Magnesium chloride	Vigorous fizzing, metal dissolves rapidly, solution warms up
Zinc	Hydrochloric acid	Zinc chloride	Steady fizzing, metal dissolves slowly
Iron	Hydrochloric acid	Iron(II) chloride	Slow fizzing, very slow dissolving, pale green solution
Magnesium	Sulfuric acid	Magnesium sulfate	Vigorous fizzing, metal dissolves rapidly
Zinc	Sulfuric acid	Zinc sulfate	Steady fizzing
Copper	Hydrochloric acid	No reaction	No fizzing, metal remains unchanged

Naming Salts

The name of the salt depends on the metal and the acid used:

• Hydrochloric acid produces chloride salts
• Sulfuric acid produces sulfate salts
• Nitric acid produces nitrate salts

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Displacement Reactions

A displacement reaction occurs when a more reactive metal takes the place of a less reactive metal in a compound. The more reactive metal displaces the less reactive metal from its salt solution.

General equation:

reactive metal + less reactive metal salt → reactive metal salt + less reactive metal

For example:

• Magnesium + copper sulfate → magnesium sulfate + copper
• Magnesium is more reactive than copper, so it displaces copper from the copper sulfate solution.

graph LR
    A["More Reactive Metal<br/>(e.g. Magnesium)"] -->|"Displaces"| B["Less Reactive Metal<br/>(e.g. Copper)"]
    C["Metal Salt Solution<br/>(e.g. Copper Sulfate)"] -->|"Reacts with<br/>more reactive metal"| D["New Salt Formed<br/>(e.g. Magnesium Sulfate)"]
    B -->|"Appears as"| E["Solid Metal Deposit<br/>(e.g. brown copper coating)"]

    style A fill:#e74c3c,color:#fff
    style B fill:#f39c12,color:#fff
    style C fill:#3498db,color:#fff
    style D fill:#2ecc71,color:#fff
    style E fill:#9b59b6,color:#fff

Predicting Displacement Reactions

Use the reactivity series to predict whether a displacement reaction will occur:

Combination	Will it react?	Reason
Iron + copper sulfate	Yes	Iron is more reactive than copper
Copper + iron sulfate	No	Copper is less reactive than iron
Zinc + magnesium chloride	No	Zinc is less reactive than magnesium
Magnesium + zinc chloride	Yes	Magnesium is more reactive than zinc

Exam Tip: If the standalone metal is ABOVE the metal in the compound in the reactivity series, a displacement reaction WILL occur. If it is below, NO reaction takes place. Always justify your answer by referring to relative reactivity.

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Explaining Reactivity in Terms of Electron Loss

The reactivity of a metal is related to its tendency to form positive ions by losing electrons. Metals that lose electrons more easily are more reactive.

• Group 1 metals (e.g. potassium, sodium) have only one electron in their outer shell, which is easily lost. They are very reactive.
• Transition metals (e.g. iron, copper) hold onto their outer electrons more tightly. They are less reactive.
• As you go down Group 1, atoms get larger, the outer electron is further from the nucleus and more easily lost, so reactivity increases.

This can be summarised:

More reactive metals lose electrons more easily → they form positive ions more readily → they react more vigorously.

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Practical: Investigating Reactivity

A common practical to investigate the reactivity series involves adding small pieces of different metals to dilute hydrochloric acid and observing the rate of fizzing:

1. Place equal-sized pieces of magnesium, zinc, iron, and copper into separate test tubes.
2. Add the same volume and concentration of dilute hydrochloric acid to each.
3. Observe and record the rate of gas production (fizzing).
4. Use a burning splint to confirm hydrogen gas is produced.

Expected results: Magnesium fizzes most vigorously, then zinc, then iron. Copper shows no reaction.

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Summary

• The reactivity series ranks metals from most reactive (potassium) to least reactive (platinum).
• Metals react with water to form metal hydroxides and hydrogen.
• Metals react with dilute acids to form salts and hydrogen.
• A displacement reaction occurs when a more reactive metal replaces a less reactive metal in a compound.
• The reactivity of metals is linked to the tendency to lose electrons and form positive ions.
• Metals that lose electrons more easily are more reactive.
• Hydrogen is included in the reactivity series as a reference point: metals above it react with dilute acids, metals below it do not.

Exam Tip: Displacement reaction questions are very common. Always state which metal is more reactive and explain that it "displaces" the less reactive metal. If asked to write a word equation, remember the format: reactive metal + less reactive metal compound → new compound + displaced metal.

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Worked Example: Writing Balanced Symbol Equations

Balanced symbol equations are a regular source of marks. Work through each reaction carefully, checking that atoms of every element balance on both sides.

Example 1 — Magnesium with hydrochloric acid

1. Write the word equation: magnesium + hydrochloric acid → magnesium chloride + hydrogen
2. Write unbalanced symbols: Mg + HCl → MgCl2 + H2
3. Balance Cl: place a 2 in front of HCl.
4. Balance H: 2 H on each side — balanced.

Final equation: Mg + 2HCl → MgCl2 + H2

Example 2 — Zinc with sulfuric acid

1. Word equation: zinc + sulfuric acid → zinc sulfate + hydrogen
2. Symbols: Zn + H2SO4 → ZnSO4 + H2
3. Check: 1 Zn, 2 H, 1 S, 4 O on each side — already balanced.

Example 3 — Iron displacing copper from copper(II) sulfate

1. Word equation: iron + copper(II) sulfate → iron(II) sulfate + copper
2. Symbols: Fe + CuSO4 → FeSO4 + Cu — balanced.
3. Ionic half-equations: Fe → Fe2+ + 2e- (oxidation); Cu2+ + 2e- → Cu (reduction).

Common mistake: Students often write "Mg + HCl → MgCl + H" and forget that chlorine forms Cl- ions and hydrogen exists as H2. Always include the correct formulae (MgCl2, H2) before balancing — changing formulae to balance an equation is a serious error.

Common mistake: Reversing the reactivity series order under pressure. Potassium is the most reactive of the common metals in the series above — not sodium. Recite the mnemonic in order at least twice during revision to lock it in.

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Metal-Acid vs Metal-Water Reactions Compared

Feature	Metal + water	Metal + dilute acid
Products	Metal hydroxide + hydrogen	Salt + hydrogen
Metals that react	K, Na, Li, Ca (cold); Mg (steam)	K, Na, Li, Ca, Mg, Al, Zn, Fe
Rate	Slower for most metals	Faster for the same metal
Hydrogen test	Squeaky pop with burning splint	Squeaky pop with burning splint
Typical observation	Fizzing, floating, dissolving	Fizzing, metal dissolves, warming

Answering at different grade levels

Exam-style question (4 marks): A student adds small, equal-sized pieces of magnesium, zinc, iron and copper to separate test tubes of dilute hydrochloric acid. Describe what the student would see and explain the results in terms of reactivity.

Grade 4–5 response: Magnesium fizzes fastest and disappears quickly. Zinc fizzes more slowly. Iron fizzes very slowly. Copper does not react. This is because magnesium is the most reactive and copper is the least reactive.

Grade 8–9 response: Magnesium reacts most vigorously, producing rapid effervescence of hydrogen gas and dissolving quickly to form a colourless magnesium chloride solution (Mg + 2HCl → MgCl2 + H2). Zinc reacts steadily; iron reacts slowly, producing a pale-green iron(II) chloride solution. Copper shows no reaction because it lies below hydrogen in the reactivity series and cannot lose electrons to H+ ions. Reactivity decreases in the order Mg > Zn > Fe > Cu because more reactive metals lose electrons from their outer shell more readily, undergoing oxidation (Mg → Mg2+ + 2e-) while H+ ions are simultaneously reduced to H2 (2H+ + 2e- → H2).

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AQA alignment: This content is aligned with AQA GCSE Chemistry (8462) specification section 5.4 Chemical changes — specifically 5.4.1.1 Metal oxides, 5.4.1.2 The reactivity series, 5.4.1.4 Oxidation and reduction in terms of electrons and 5.4.2.1 Reactions of acids with metals. Assessed on Paper 1.