A student notices that the burette used in a titration was not rinsed with the acid solution before being filled, but was rinsed only with distilled water. Explain how this error would affect the titre value obtained, compared with the true titre.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A student completes a titration using sulfuric acid in the burette and sodium hydroxide solution in the conical flask, with methyl orange as the indicator. After the titration, the student realises the burette was rinsed with distilled water only before being filled with sulfuric acid.
Model answer (4 marks)
The rinsing with water dilutes the acid in the burette, so the effective concentration of H₂SO₄ is lower than the stated 0.10 M. Consequently, a larger volume of acid is required to neutralise the same amount of NaOH, so the recorded titre will be larger than the true titre. This is a systematic error – all repeat titrations will give the same over‑estimation and the results will be inaccurate, though they may still be precise.
Examiner tips
- State the dilution effect first, then the consequence on volume, then the systematic nature of the error.
- Use the exact terms: ‘diluted’, ‘larger volume’, ‘higher titre’, ‘systematic error’, ‘inaccurate but precise’.
- Keep the answer to 4 points – one per mark.
Mark scheme (4 marks)
- The acid in the burette is diluted / the concentration of sulfuric acid in the burette is lower than intended
- More acid would be needed to neutralise the sodium hydroxide / a larger volume of acid is required to reach the end-point
- The titre value recorded would be larger / higher than the true titre
- This is a systematic error, so all repeat titres would be affected in the same way / the results would not be accurate (but could be precise / concordant)
Key terms in this question
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Acid-base titrations questions
- Describe how a student would carry out an acid-base titration to find the volume…
- A student carries out a titration to determine the end point of a reaction betwe…
- A student carries out a titration using phenolphthalein indicator to determine t…
- A student carries out a titration to find the concentration of a solution of sod…