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J248 · PAG6; C7Practical Activity GroupsCore

PAG6: Titration Measurements

A pipette with the appropriate filler delivers a defined aliquot to a conical flask. A burette measures the volume delivered from a change in reading. Follow the approved rinsing and filling method; water remaining in a burette can dilute its solution, and an unfilled tip can cause a misleading first delivery. Read the appropriate meniscus at eye level.

35 min Video by Malmesbury Education Practical Activity Groups
Neutralisation Titration - GCSE Science Required Practical (Triple)Curated by Kepler, not produced by us. Watch it before the notes below.
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Before you start

  • Use your teacher’s tier checklist: this overview can include Higher-only material, and is not a tier-specific revision list.
  • OCR Gateway A separate GCSE Chemistry J248. This is a suitable practical-group example; centres can choose other activities covering the required apparatus and techniques.
  • Read a graduated scale and distinguish an acid, an alkali and an indicator.
  • Use the centre’s approved supervised method, apparatus, heating and disposal arrangements. Written preparation does not replace performing and recording the practical activities.

Watch, pause, try

Video by Malmesbury Education. Use the demonstration alongside this lesson’s specification reference and written explanations.

Viewing focus: Explain measured delivery and endpoint technique

After watching, attempt these questions before opening the answers. You can also use the written lesson below.

After watching 1: How is a titre obtained?

Show answer and reasoning

Subtract initial from final burette reading. The titre is a change in reading.

After watching 2: Why add slowly near the endpoint?

Show answer and reasoning

To reduce overshoot and judge the change more precisely. The signal can be passed by a small extra delivery.

What you'll be able to do

  • Explain measured delivery and endpoint technique
  • Calculate titres and select suitable repeat data
  • Use a balanced reaction for concentration calculations where assessed
1

Measure delivered volumes correctly

A pipette with the appropriate filler delivers a defined aliquot to a conical flask. A burette measures the volume delivered from a change in reading. Follow the approved rinsing and filling method; water remaining in a burette can dilute its solution, and an unfilled tip can cause a misleading first delivery. Read the appropriate meniscus at eye level.

Record both initial and final burette readings, then subtract initial from final to obtain the titre. The burette scale increases downward. The initial reading need not be zero, and a final reading alone is not the volume delivered. Distinguish the precision of the reading from the repeatability of the procedure.

2

Approach a reproducible endpoint

Use a suitable indicator in the specified small amount and a white background to help observe its change. Mix by swirling and approach the endpoint slowly, using dropwise addition near the change. A rough trial can locate the approximate region before careful repeat titrations.

The indicator endpoint is an observable signal chosen to approximate the required chemical condition. Do not assume every indicator works for every acid–base combination. Use the stated concordance rule when selecting repeat titres, retain all raw readings, and avoid averaging an obvious overshoot with careful concordant results merely to increase the number of readings.

3

Keep volume comparisons distinct from amount calculations

Reacting volumes can be determined experimentally without assuming equal concentrations or equal mole ratios. For concentration work, first use the balanced equation and c = n/V with compatible units; 1000 cm³ = 1 dm³. A one-to-one HCl/NaOH example does not justify using equal reacting amounts for every acid.

Concentration calculations may have tier-specific requirements, so use the qualification reference attached to this guide. Extra distilled water added to the conical flask can change the concentration in that flask but not the amount of the original pipetted solute. Distinguish that operation from diluting the stock solution before pipetting.

4

Worked applications

Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.

Example 1A burette initially reads 1.20 cm³ and finally 25.85 cm³. Find the titre.
1Delivered volume = final − initial.
225.85 − 1.20 = 24.65.
Answer
24.65 cm³.
Example 2For a stated 1:1 HCl/NaOH reaction, 25.0 cm³ of alkali requires 20.0 cm³ of 0.100 mol dm⁻³ acid. Find the alkali concentration where this calculation is assessed.
1Acid amount = 0.100 × 0.0200 = 0.00200 mol.
2Alkali amount is the same for this equation.
3Alkali concentration = 0.00200/0.0250.
Answer
0.0800 mol dm⁻³.

Common mistakes to avoid

Assuming every titration is 1:1.
Use the balanced equation.
Averaging every trial regardless of the concordance rule.
Retain the data and justify the selected mean.

Key takeaways

  • You can explain measured delivery and endpoint technique.
  • You can calculate titres and select suitable repeat data.
  • You can use a balanced reaction for concentration calculations where assessed.

Apply it in an exam

Question 1: For a stated 1:1 HCl/NaOH reaction, 25.0 cm³ of alkali requires 20.0 cm³ of 0.100 mol dm⁻³ acid. Find the alkali concentration where this calculation is assessed.

Show answer and reasoning

0.0800 mol dm⁻³.

  • Acid amount = 0.100 × 0.0200 = 0.00200 mol.
  • Alkali amount is the same for this equation.
  • Alkali concentration = 0.00200/0.0250.

Explore further

Return to this tomorrow

Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.

  • Why add slowly near the endpoint?
  • Does extra pure water in the flask remove the original solute amount?

Test yourself

Answer a few questions, then review anything you missed.

Next step

Keep practising

Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.

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