# A student carries out a titration using phenolphthalein indicator to determine the volume of sulfuric acid needed to neutralise a solution of potassium hydroxide. The student obtains a rough titre and then repeats the titration to obtain concordant results. Explain why the student carries out multiple titrations and state what is done with the concordant results to obtain a reliable final titre.

> Cambridge International IGCSE Chemistry (0620) — 12.2 Acid-base titrations · Explain · 4 marks

## Mark scheme (4 marks)

1. Multiple titrations are carried out to check reproducibility / identify anomalous results
2. The rough titre is used to identify the approximate end-point so that the final titrations can be performed more accurately / dropwise near the end-point
3. Concordant results are titres that agree closely with each other (within 0.10 cm³ / accept within a small range)
4. The concordant results are averaged (mean calculated) to obtain the final titre; the rough titre is excluded from this calculation

## Key terms

- [titration](https://www.gradenine.co.uk/glossary/titration)
- [concordant results](https://www.gradenine.co.uk/glossary/concordant-results)
- [rough titre](https://www.gradenine.co.uk/glossary/rough-titre)

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-carries-out-a-titration-f26e7927) · Published by Druglandscape Ltd.