A flame photometer is calibrated using standard solutions of sodium ions.
| Concentration of sodium ions in mg dm−3\mathrm{mg\,dm^{-3}}mgdm−3 | 0 | 2.0 | 4.0 | 6.0 | 8.0 | 10.0 |
|---|---|---|---|---|---|---|
| Reading | 0 | 18 | 36 | 54 | 72 | 90 |
10.0 cm3\mathrm{cm^{3}}cm3 of river water is diluted with distilled water to a total volume of 100.0 cm3\mathrm{cm^{3}}cm3. The diluted sample gives a reading of 63.
What is the concentration of sodium ions in the undiluted river water?
0.70 mg dm−3\mathrm{mg\,dm^{-3}}mgdm−3
7.0 mg dm−3\mathrm{mg\,dm^{-3}}mgdm−3
70 mg dm−3\mathrm{mg\,dm^{-3}}mgdm−3
630 mg dm−3\mathrm{mg\,dm^{-3}}mgdm−3
35 exam-style questions on Edexcel GCSE Chemistry 10.1 Qualitative analysis: tests for ions, covering 10.1.1 Principles of ion tests and flame tests, 10.1.2 Tests for cations and for ammonia, 10.1.3 Tests for anions, 10.1.4 Identification of ions in unknown salts, and 10.1.5 Instrumental methods of analysis. Each one has a worked solution and a mark scheme showing where the marks go.