Titration Calculations
Build confidence in Titration Calculations for GCSE Chemistry with this free worksheet and full mark scheme — Higher-tier exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) Higher topic: use the titre volume and a known concentration to calculate an unknown concentration through moles.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
This is a Higher tier only topic, so there's no Foundation paper — only the Higher worksheet and mark scheme below.
Topic overview
Titration calculations find the concentration of an unknown solution using a solution of known concentration. This is a Triple and Higher-only topic.
The method has four steps: calculate the moles of the known solution using moles = concentration × volume in dm³; use the balanced equation to find the moles of the unknown; then calculate its concentration using concentration = moles ÷ volume.
The ratio from the balanced equation is essential. If one mole of acid reacts with two moles of alkali, the moles are not simply equal, and assuming a one to one ratio is the most common error in these calculations.
Revision notes
The four steps
1. Moles of known = concentration × volume in dm³.
2. Use the balanced equation ratio to find the moles of the unknown. 3. Concentration of unknown = moles ÷ its volume in dm³. 4. Convert to g/dm³ if the question asks, by multiplying by the Mr.
Using the ratio
The large numbers in the balanced equation give the mole ratio.
For H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O, one mole of sulfuric acid reacts with two moles of sodium hydroxide. Never assume a one to one ratio without checking.
Accuracy
Concordant titres — those within 0.1 cm³ of each other — are used to calculate a mean.
Anomalous results and the rough titre are excluded. Using the mean of concordant results improves the reliability of the calculated concentration.
Key points
- Moles = concentration × volume in dm³.
- Use the balanced equation to find the mole ratio.
- Concentration = moles ÷ volume in dm³.
- Never assume a one to one ratio.
- Convert cm³ to dm³ before substituting.
- Use concordant titres to calculate a mean.
Worked examples
Example 1
25 cm³ of NaOH is neutralised by 20 cm³ of 0.1 mol/dm³ HCl. The ratio is 1:1. Calculate the concentration of the NaOH. [4 marks]
Model answer
Volume of HCl = 20 ÷ 1000 = 0.02 dm³ (1 mark). Moles of HCl = 0.1 × 0.02 = 0.002 mol (1 mark). The ratio is 1:1, so moles of NaOH = 0.002 mol (1 mark). Concentration = 0.002 ÷ 0.025 = 0.08 mol/dm³ (1 mark).
Example 2
Explain why the balanced equation must be used in a titration calculation. [2 marks]
Model answer
The balanced equation gives the ratio in which the substances react (1 mark), and this ratio is not always one to one, so the moles of the unknown cannot simply be assumed equal to the moles of the known (1 mark).
Example 3
Explain what is meant by concordant titres. [2 marks]
Model answer
Concordant titres are results that are within 0.1 cm³ of each other (1 mark), and only these are used to calculate the mean titre so that the result is reliable (1 mark).
Common mistakes
Assuming a one to one ratio.
Always read the balanced equation. Sulfuric acid reacts with two moles of a 1+ alkali.
Forgetting to convert cm³ to dm³.
Both volumes must be in dm³ before substituting.
Using the rough titre in the mean.
Only concordant titres are averaged.
Dividing by the wrong volume at the end.
Divide by the volume of the UNKNOWN solution, not the known one.
Exam tips
- Convert both volumes to dm³ first.
- Write the balanced equation and read the ratio from it.
- Divide by the unknown solution's volume at the final step.
- Remember this is a Triple and Higher-only topic.
Key terms
- Titration
- A technique to find an unknown concentration accurately.
- Titre
- The volume of solution delivered from the burette.
- Concordant
- Results within 0.1 cm³ of each other.
- Mole ratio
- The ratio in which substances react, from the balanced equation.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.