# A student notices that their repeated measurements of the boiling point of a salt solution give values that are all slightly higher than the accepted boiling point of pure water, and that the values are all very close to each other. Explain what these results tell the student about the accuracy and repeatability of their measurements.

> OCR GCSE Physics A: Gateway Science (J249) — P9 Practical skills · Explain · 4 marks

> A student measures the boiling point of a salt solution three times and records: 101.8 °C, 101.9 °C, and 101.7 °C. The accepted boiling point of pure water at standard pressure is 100.0 °C.

## Mark scheme (4 marks)

1. The results are repeatable because the values are all very close to each other / there is only a small range between the measurements.
2. The results are not accurate because they are all far from / do not match the accepted value (100.0 °C).
3. The consistent difference from the accepted value suggests a systematic error in the investigation.
4. The higher boiling point is expected / not an error because dissolving salt in water raises its boiling point, so the accepted value for pure water does not apply here.

## Key terms

- [accuracy](https://www.gradenine.co.uk/glossary/accuracy)
- [repeatability](https://www.gradenine.co.uk/glossary/repeatability)

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](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-notices-that-their-repeated-bd60abb9) · Published by Druglandscape Ltd.