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To write an ionic equation, split aqueous ionic compounds into ions, then remove the spectator ions that are unchanged. Free notes and 11 questions answered.
Writing Ionic Equations for Displacement Reactions is part of Reactivity of metals in GCSE AQA Higher Chemistry.
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To write an ionic equation, split aqueous ionic compounds into ions, then remove the spectator ions that are unchanged. Free notes and 11 questions answered.
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Use this lesson to stay inside Reactivity of metals while connecting the detail back to the wider Topic 4: Chemical changes topic.
Read the core explanations from Writing Ionic Equations for Displacement Reactions before testing yourself from memory.
When zinc metal displaces copper from copper sulphate solution, something fascinating happens. The full equation shows lots of ions floating around, but only some actually do the work. Ionic equations strip away the noise and show you exactly what's happening at the atomic level.
This isn't just academic - it's how chemists understand reactions in batteries, metal extraction, and corrosion. You'll see this technique throughout A-level and beyond.
Think of it like a queue for a popular restaurant. If someone more important arrives, they can push in front of someone less important. In chemistry, 'importance' is determined by the reactivity series.
Picture a football match where some players are actively involved in the action, while others just watch from the sidelines. Spectator ions are the watchers - they're there, but they don't affect the outcome.
Let's watch the transformation happen step by step. We'll start with a full equation and strip it down to show only what matters.
Worked example: Converting a Full Equation to an Ionic Equation
Convert this displacement reaction to an ionic equation: Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
Answer: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)
Notice how much cleaner this looks. The ionic equation tells the real story: zinc atoms give up electrons to become Zn²⁺ ions, while Cu²⁺ ions grab those electrons to become copper atoms.
Not every metal can displace every other metal. The reactivity series is your guide - it tells you who can push out whom.
Reactivity Series (most to least reactive):Potassium > Sodium > Lithium > Calcium > Magnesium > Aluminium > Carbon > Zinc > Iron > Tin > Lead > Hydrogen > Copper > Silver > Gold
The rule is simple: metals higher up can displace metals lower down from their compounds. Zinc can displace copper because zinc is higher in the series.
Worked example: Predicting and Writing Ionic Equations
Will magnesium displace silver from silver nitrate solution? If yes, write the ionic equation.
Answer: Mg(s) + 2Ag⁺(aq) → Mg²⁺(aq) + 2Ag(s)
Most displacement reactions follow the same pattern. Once you recognise it, writing ionic equations becomes straightforward.
The Universal Pattern:More reactive metal + Metal ion → Metal ion + Less reactive metal
The key is identifying which ions are doing the actual work and which are just spectating. Anions like SO₄²⁻, NO₃⁻, and Cl⁻ are usually spectators in displacement reactions.
Trap Alert: Many students forget to balance ionic equations. Remember, Fe³⁺ needs 3 electrons, so you might need 3 atoms of the displacing metal to balance the charges.
Examiners love testing ionic equations because they reveal whether you truly understand what's happening in reactions. Here's how to nail these questions every time.
Command Word Decoder:
'Write the ionic equation' - Remove spectator ions and balance the equation. Always include state symbols.
'Explain why no reaction occurs' - Check the reactivity series. If the metal is trying to displace something more reactive, no reaction happens.
'Identify the spectator ions' - Look for ions that appear unchanged on both sides of the full equation.
Mark-Winning Strategy: Always work systematically. Write the full equation first, then identify and remove spectators. This prevents careless errors and shows clear working for method marks.
Exam precision note: In Writing Ionic Equations for Displacement Reactions - Oxidation and reduction in terms of electrons (HT only) - Reactivity of metals, always identify the key chemical idea first, then link it to evidence, data, or an equation. A high-scoring GCSE answer names the particles involved, states what changes, and justifies the conclusion using correct scientific language. Where calculations are used, show each step with units and keep significant figures sensible. Finally, check that terminology matches AQA wording so your answer is unambiguous and mark-scheme friendly.
For AQA Higher Tier, ionic equations for displacement reactions should show which ions are oxidised and which ions are reduced. Removing spectator ions helps you focus on the species that actually change during the reaction, which makes the electron transfer clearer.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
To write an ionic equation, write the full balanced equation, split the aqueous ionic compounds into ions, then remove the spectator ions that appear unchanged on both sides. For Zn + CuSO₄ → ZnSO₄ + Cu, removing SO₄²⁻ gives Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s).
Spectator ions are ions that are present in a reaction mixture but do not take part in the actual reaction, so they remain unchanged. In displacement reactions, anions such as SO₄²⁻, NO₃⁻ and Cl⁻ are usually spectators.
An ionic equation is balanced so that atoms and charges match on both sides. Mg(s) + 2Ag⁺(aq) → Mg²⁺(aq) + 2Ag(s) needs 2 Ag to balance the charges, and Fe³⁺ needs 3 electrons, so more atoms of the displacing metal may be needed.
The ionic equation for magnesium displacing silver from silver nitrate is Mg(s) + 2Ag⁺(aq) → Mg²⁺(aq) + 2Ag(s). The nitrate ions are spectators, and 2 silver ions are needed to balance the charge of one Mg²⁺ ion.
A metal cannot displace a more reactive metal from its compound, so no reaction happens. Metals higher in the reactivity series displace metals lower down; for example, zinc displaces copper because zinc is higher in the series.
Ionic equations are useful because they remove spectator ions and show only the species that actually change, which makes the electron transfer clearer. In Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s), zinc atoms give up electrons and Cu²⁺ ions gain them.
The ionic equation for zinc and copper sulphate is Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s). The SO₄²⁻ ions are spectator ions, so they are removed. Zinc atoms give up electrons to become Zn²⁺ ions, while Cu²⁺ ions grab those electrons to become copper atoms.
Anions such as SO₄²⁻, NO₃⁻ and Cl⁻ are usually spectator ions in displacement reactions. They appear unchanged on both sides of the full equation because they don't take part in the actual reaction, so they are left out of the ionic equation.
Only compounds marked (aq) are split into ions when writing an ionic equation; solids stay as they are. For Zn(s) + CuSO₄(aq), only CuSO₄ and ZnSO₄ are split, giving Cu²⁺, Zn²⁺ and SO₄²⁻ ions.
Ionic equations should always include state symbols. The ionic equation for magnesium and silver nitrate, for example, is Mg(s) + 2Ag⁺(aq) → Mg²⁺(aq) + 2Ag(s).
Most displacement reactions follow the pattern: more reactive metal + metal ion → metal ion + less reactive metal. The more reactive metal loses electrons and is oxidised, while the metal ion gains electrons and is reduced.