A scientist uses flame emission spectroscopy to find the concentration of sodium ions in river water.
She measures the intensity of light given out by standard solutions of sodium ions. She then dilutes 1 cm31\,\mathrm{cm^{3}}1cm3 of the river water to 10 cm310\,\mathrm{cm^{3}}10cm3 with pure water and measures the diluted sample.
| Solution | Concentration of sodium ions (mg/dm3\mathrm{mg/dm^{3}}mg/dm3) | Intensity |
|---|---|---|
| Standard 1 | 0.0 | 0 |
| Standard 2 | 2.0 | 18 |
| Standard 3 | 4.0 | 36 |
| Standard 4 | 6.0 | 54 |
| Standard 5 | 8.0 | 72 |
| Diluted river water | ? | 45 |
What is the concentration of sodium ions in the original river water?
4.5 mg/dm34.5\,\mathrm{mg/dm^{3}}4.5mg/dm3
5.0 mg/dm35.0\,\mathrm{mg/dm^{3}}5.0mg/dm3
0.50 mg/dm30.50\,\mathrm{mg/dm^{3}}0.50mg/dm3
50 mg/dm350\,\mathrm{mg/dm^{3}}50mg/dm3
107 exam-style questions on OCR GCSE Chemistry 4.2 Identifying the products of chemical reactions, covering 4.2.1 Tests to identify gases, 4.2.2 Tests for aqueous ions and flame tests, and 4.2.3 Instrumental methods of analysis. Each one has a worked solution and a mark scheme showing where the marks go.