Ch 4 · Reactivity Series · O Level Chemistry 5070
Topic 4 of 6 in Metals — O Level Chemistry 5070 — 37 lessons.
Introduction
The reactivity series ranks metals by how readily they react, and it is the key to predicting which metal displaces which, how a metal can be extracted from its ore and why some metals corrode while others do not. You need to know the order by heart, describe the set reactions with water and acid, and, most importantly, deduce an order from experimental data you have never seen before.
Key ideas — The order
From most to least reactive: potassium, sodium, calcium, magnesium, aluminium, (carbon), zinc, iron, (hydrogen), copper, silver, gold. Carbon and hydrogen are non-metals, but they are placed in the series because they help predict extraction and acid reactions: carbon can reduce the oxides of metals below it, and only metals above hydrogen react with dilute acids.
🧑🏫 Teacher's explanation
Think of the reactivity series as a 'social hierarchy' of metals. The metals at the top are extremely 'eager' to get rid of their electrons and become positive ions. They are like energetic teenagers who can't wait to react with anything they touch, such as water or acid. The metals at the bottom are much more 'calm' and stable; they prefer to stay as they are and don't react with much at all.
📖 Definitions
🔍 Worked example — Easy
A student places a piece of magnesium (Mg) into a test tube containing dilute hydrochloric acid (HCl). Predict if a reaction occurs and state the observation.
🔍 Worked example — Standard
Calculate the mass of magnesium oxide produced when 2.4 g of magnesium reacts completely with oxygen in the reaction: 2Mg + O_2 arrow 2MgO. (A_r: Mg = 24, O = 16)
🔍 Worked example — Exam-style
In an experiment, a piece of zinc (Zn) is added to a solution of copper(II) sulfate (CuSO_4). Will a reaction occur? Explain using the reactivity series.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
Key ideas — Reactions with water, steam and dilute acid
The higher the metal in the series, the faster and more vigorous its reaction.
🧑🏫 Teacher's explanation
Think of the reactivity series as a 'social hierarchy' of metals. The metals at the top are extremely eager to give away their electrons to become positive ions, making them highly reactive and 'aggressive' in their interactions. The metals at the bottom are much more 'introverted' and prefer to stay in their metallic form, refusing to react with things like water or dilute acids.
📖 Definitions
🔍 Worked example — Easy
A piece of magnesium is reacted with steam. Write the balanced chemical equation for this reaction.
🔍 Worked example — Standard
Calculate the mass of hydrogen gas produced when 12.0 g of magnesium reacts completely with excess steam. Mg = 24, H = 1.
🔍 Worked example — Exam-style
A student places a piece of Zinc in dilute hydrochloric acid. Predict the observation and write the balanced equation. Zn = 65, H = 1, Cl = 35.5.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
(a) Explain why copper does not react with the acid. [1] (b) Write a balanced chemical equation for the reaction between Zinc and hydrochloric acid. [2] [3 marks]
Key ideas — Deducing an order from experimental results
Displacement reactions. A more reactive metal displaces a less reactive metal from a solution of its salt. Zinc placed in copper(II) sulfate solution becomes coated with brown copper and the blue solution fades:
🧑🏫 Teacher's explanation
Think of the reactivity series as a 'social hierarchy' of metals. In this hierarchy, the most reactive metals are the 'extroverts'—they are desperate to give away their electrons and move into a solution. The less reactive metals are the 'introverts'—they prefer to stay as solid atoms and hold onto their electrons tightly.
📖 Definitions
🔍 Worked example — Easy
A student performs a series of displacement reactions and records the results in a table. Metal X reacts with Copper(II) sulfate to produce solid copper. Metal Y reacts with Zinc sulfate to produce solid zinc. Metal Z reacts with Iron(II) sulfate to produce solid iron. Which metal is the most reactive: X, Y, or Z?
🔍 Worked example — Exam-style
A student observes that heating Magnesium oxide (MgO) with Carbon (C) results in no reaction. However, heating Iron(III) oxide (Fe_2O_3) with Carbon (C) produces Iron (Fe) and Carbon dioxide (CO_2). Based on this, rank the reactivity of Mg and Fe relative to Carbon.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
Worked example
Question. Four metals, W, X, Y and Z, were tested. W reacted violently with cold water. X reacted with dilute acid but not with cold water. Y did not react with dilute acid. Z displaced X from a solution of its sulfate but did not react with cold water. (a) Place the metals in order of reactivity, most reactive first. [2] (b) Write an ionic equation for the reaction of Z with a solution of X sulfate, given that both form 2+ ions. [2]
🔍 Worked example — Easy
Metal A reacts vigorously with cold water to produce a metal hydroxide and hydrogen gas. Metal B reacts slowly with dilute hydrochloric acid but does not react with cold water. Which metal is more reactive?
🔍 Worked example — Standard
A student adds solid Zinc to a solution of Copper(II) sulfate. The blue color of the solution fades and a reddish-brown solid forms. Write the balanced ionic equation for this reaction.
🔍 Worked example — Exam-style
Four metals (P, Q, R, S) are tested. P reacts with steam but not cold water. Q reacts with dilute acid but not steam. R displaces Q from its nitrate solution. S does not react with dilute acid. Order them from most reactive to least reactive.
⚠️ Common errors
Common mistakes
Practice
Answers K, Na, Ca, Mg, Al, C, Zn, Fe, H, Cu, Ag, Au [B2, B1 if one element misplaced]. Any two of: floats, moves around on the surface, melts into a ball, fizzes, lilac flame, disappears [B2]; 2K(s) + 2H_2O(l) arrow 2KOH(aq) + H_2(g) [M1 species, A1 balanced with state symbols]. Zinc is below carbon in the reactivity series so carbon reduces zinc oxide to zinc [B1]; magnesium is above carbon so carbon cannot remove oxygen from magnesium oxide [B1]. Aluminium reacts with oxygen to form a thin, unreactive layer of aluminium oxide on its surface [B1]; this layer prevents water reaching the metal underneath [B1]. Mg(s) + mathrmFe^2+(aq) arrow mathrmMg^2+(aq) + Fe(s) [B1]; magnesium is oxidised because it loses electrons [B1].