A factory uses flame emission spectroscopy to monitor water used to wash glass. The water contains sodium ions and potassium ions. The water is treated to reduce the concentration of sodium ions while leaving most of the potassium ions in the water.
Table 1 shows one main line for each metal ion.
| Metal ion | Wavelength of main line in nm |
|---|---|
| Sodium | 589 |
| Potassium | 766 |
Table 2 shows calibration data and the line intensities measured before and after treatment. At each wavelength, line intensity is directly proportional to concentration.
| Wavelength in nm | Concentration of standard solution in mg/dm³ | Intensity from standard solution in arbitrary units | Intensity before treatment in arbitrary units | Intensity after treatment in arbitrary units |
|---|---|---|---|---|
| 589 | 4.0 | 32 | 56 | 12 |
| 766 | 3.0 | 18 | 30 | 27 |
A technician claims that the treatment removes all the sodium ions from the water.
Evaluate this claim using Tables 1 and 2.
Calculate the concentration of each metal ion in the water after treatment.
The treatment is acceptable only if:
Evaluate whether the treatment is acceptable.
93 exam-style questions on AQA GCSE Chemistry 8.3 Identification of ions by chemical and spectroscopic means, covering 8.3.1 Flame tests, 8.3.2 Metal hydroxides, 8.3.3 Carbonates, 8.3.4 Halides, 8.3.5 Sulfates, 8.3.6 Instrumental methods, and 8.3.7 Flame emission spectroscopy. Each one has a worked solution and a mark scheme showing where the marks go.