A company recovers lithium from used lithium-ion batteries by dissolving the crushed batteries in acid. A chemist uses flame emission spectroscopy to identify the metal ions in the solution, and a flame photometer to measure the concentration of lithium ions.
The table shows the wavelengths of the main lines in the emission spectra of some metal ions, to the nearest nm.
| Metal ion | Wavelengths of lines / nm |
|---|---|
| lithium | 610, 671 |
| sodium | 589 |
| potassium | 404, 767 |
| calcium | 423, 443 |
| copper | 511, 515, 522 |
The spectrum of the battery solution has lines at 423 nm, 443 nm, 589 nm, 610 nm and 671 nm.
Explain why a flame test would not be suitable for identifying all of the metal ions in the battery solution.
Deduce which metal ions in the table are present in the battery solution and which are absent. Justify your answer.
The chemist calibrates the flame photometer using standard lithium solutions.
| Concentration of lithium ions / mg dm−3\mathrm{mg\,dm^{-3}}mgdm−3 | 0 | 5.0 | 10.0 | 15.0 | 20.0 |
|---|---|---|---|---|---|
| Meter reading | 2.0 | 14.0 | 26.0 | 38.0 | 50.0 |
The chemist dilutes 25.0 cm3\mathrm{cm^{3}}cm3 of the battery solution to 250 cm3\mathrm{cm^{3}}cm3 with distilled water. The diluted solution gives a meter reading of 32.0.
Calculate the mass, in g, of lithium ions in 2.00 dm3\mathrm{dm^{3}}dm3 of the undiluted battery solution.
The undiluted battery solution gave a meter reading above 50.0. Explain why the chemist diluted the solution before measuring it.
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.