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2.1.4Organic Chemistry

Ionic Equations — Edexcel AS Chemistry Revision Notes & Topical Questions

5 min read 6 parts Lesson 4 of 42

📚 Edexcel AS Chemistry Hub / Topical Revision
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Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
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Part 1 of 6From Full to Ionic Equations

1
Write the balanced full equation with state symbols.
2
Split every aqueous ionic compound into its separate ions.
3
Leave solids, liquids, gases and covalent molecules as formulae.
4
Cross out ions that appear unchanged on both sides, the spectator ions.
5
Write the remaining species as the ionic equation and check that charge and atoms balance.
6
Ionic equations show only the species that really change, which makes patterns in reactions easier to see.

Part 2 of 6Examples

Examples
Precipitation
  • Precipitation Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s) shows barium sulfate forming.
Neutralisation
  • Neutralisation H⁺(aq) + OH⁻(aq) → H₂O(l) is common to all strong acid and alkali reactions.
Displacement
  • Displacement Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s) shows electrons moving from zinc to copper ions.
Acid with metal
  • Acid with metal Mg(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂(g) shows hydrogen ions being reduced.
Gases and solids
  • Gases and solids Species that are solids, liquids or gases stay as whole formulae because they are not dissociated into free ions.
Full equationSpectator ions
AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)Na⁺ and NO₃⁻
ZnSO₄(aq) + Mg(s) → MgSO₄(aq) + Zn(s)SO₄²⁻

Part 3 of 6Combining Half-Equations

Write each half-equation
  • Write each half-equation Show the oxidation and the reduction separately, with electrons included.
Equalise electrons
  • Equalise electrons Multiply each half-equation by a factor so that electrons lost equal electrons gained.
Add them together
  • Add them together Add the left sides and the right sides, then cancel electrons that appear on both.
Check charge
  • Check charge Total charge on the left must equal total charge on the right.

Part 4 of 6Redox Checks

Redox Checks
Atoms
  • Atoms Count each element on both sides to verify the equation is balanced.
Charge
  • Charge Add up ionic charges; they must match across the arrow.
States
  • States Add (aq), (s), (l) or (g) as required.
Identify roles
  • Identify roles Name the species oxidised and the one reduced to confirm that it is a redox reaction.

Part 5 of 6Worked Example

Question Combine the half-equations Al → Al³⁺ + 3e⁻ and Cu²⁺ + 2e⁻ → Cu to give the overall ionic equation.

  1. Lowest common multiple of 3 and 2 electrons is 6.
  2. Multiply the aluminium equation by 2: 2Al → 2Al³⁺ + 6e⁻.
  3. Multiply the copper equation by 3: 3Cu²⁺ + 6e⁻ → 3Cu.
  4. Add and cancel 6e⁻: 2Al + 3Cu²⁺ → 2Al³⁺ + 3Cu.
  5. Charge checkleft = +6, right = +6.

Answer 2Al(s) + 3Cu²⁺(aq) → 2Al³⁺(aq) + 3Cu(s)

Part 6 of 6Exam Checklist & Tips

2.1.4 – Key Points for the Exam

  • Ionic equation Equation showing only the particles that change in the reaction.
  • Spectator ion An ion that appears unchanged on both sides.
  • Half-equation Equation showing either oxidation or reduction with electrons.
  • Precipitate An insoluble solid formed in a solution.

Common Mistakes

  • Splitting solids or gases into ions.
  • Leaving spectator ions in the final ionic equation.
  • Not balancing charge as well as atoms.
  • Forgetting to multiply half-equations to equalise electrons.

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