All revision notes topics

Titration CalculationsOxford AQA IGCSE Chemistry: Revision notes

Section 1

What quantities are involved in titration calculations?

Titration calculations combine three key quantities for the acid and the alkali:

  • Moles (n) — the amount of substance
  • Concentration (c) — in mol/dm³
  • Volume (V) — in dm³

These are linked by the equation n = c × V, which is applied to both the acid and the alkali using the mole ratio from the balanced neutralisation equation.

Key termsmolesconcentrationvolume

Section 2

How do you calculate moles from titration results?

  1. Note the volume of solution with known concentration used
  2. Convert this volume to dm³ (divide cm³ by 1000)
  3. Calculate moles using n = c × V
  4. Use the mole ratio from the balanced equation to find moles of the other substance
  5. Use n = c × V (rearranged) to find the unknown concentration or volume
Example

25.0 cm³ of sodium hydroxide of concentration 0.100 mol/dm³ exactly neutralises 20.0 cm³ of hydrochloric acid. NaOH + HCl → NaCl + H2O (1:1 ratio). Moles NaOH = 0.100 × (25.0 ÷ 1000) = 0.0025 mol. Moles HCl = 0.0025 mol (1:1 ratio). Concentration HCl = 0.0025 ÷ (20.0 ÷ 1000) = 0.125 mol/dm³.

Section 3

How do you convert between mol/dm³ and g/dm³?

Concentration can also be expressed in g/dm³, which shows the mass of solute dissolved per dm³ rather than the number of moles.

To convert concentration from mol/dm³ to g/dm³, multiply by the Mr of the solute:

Concentration (g/dm³) = concentration (mol/dm³) × Mr

Example

A solution of NaOH (Mr = 40) has a concentration of 0.125 mol/dm³. Concentration in g/dm³ = 0.125 × 40 = 5 g/dm³.

Section 4

Why might the calculated (theoretical) result differ from the experimental result?

Titration calculations assume the reaction goes exactly as the balanced equation predicts, but in practice:

  • Reading errors on the burette or pipette introduce small volume errors
  • The indicator may not change colour at exactly the neutralisation point
  • Solutions may not be mixed thoroughly before the end point is reached
Common mistake

A common error is using the mole ratio incorrectly when the acid and alkali do not react 1:1 (e.g. sulfuric acid, H2SO4, reacts with 2 mol of NaOH per mole of acid) — always check the balanced equation carefully.

Must Know

  • n = c × V, where c is in mol/dm³ and V is in dm³
  • Convert volumes from cm³ to dm³ by dividing by 1000
  • Use the mole ratio from the balanced equation to link moles of acid and alkali
  • Concentration in g/dm³ = concentration in mol/dm³ × Mr
  • Repeat titrations improve accuracy and help identify anomalous results

That's the notes covered.

Carry on to the next subtopic.