A technician needs to make 25 cm325\,\mathrm{cm^{3}}25cm3 of a copper(II) ion solution that gives an intensity of 24 in a flame emission spectrometer. The technician will make it by diluting a stock solution containing 30 mg/dm330\,\mathrm{mg/dm^{3}}30mg/dm3 of copper(II) ions with pure water.
The table shows the intensities measured for standard solutions of copper(II) ions.
| Standard solution | Concentration of copper(II) ions (mg/dm3\mathrm{mg/dm^{3}}mg/dm3) | Intensity |
|---|---|---|
| Standard 1 | 0 | 0 |
| Standard 2 | 10 | 20 |
| Standard 3 | 20 | 40 |
| Standard 4 | 30 | 60 |
| Standard 5 | 40 | 80 |
What volume of the stock solution should the technician use?
25 cm325\,\mathrm{cm^{3}}25cm3
10 cm310\,\mathrm{cm^{3}}10cm3
12 cm312\,\mathrm{cm^{3}}12cm3
20 cm320\,\mathrm{cm^{3}}20cm3
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.