Question 18N.3.hl.TZ0.1c
| Date | November 2018 | Marks available | [Maximum mark: 2] | Reference code | 18N.3.hl.TZ0.1c |
| Level | hl | Paper | 3 | Time zone | TZ0 |
| Command term | Suggest | Question number | c | Adapted from | N/A |
Alloys containing at least 60 % copper reduce the presence of bacteria on their surface.The percentage of copper in brass, an alloy of copper and zinc, can be determined by UV-vis spectrometry.
A sample of brass is dissolved in concentrated nitric acid and then made up to 250.0 cm3 with water before analysis.
Cu (s) + 4HNO3 (aq) → Cu(NO3)2 (aq) + 2NO2 (g) + 2H2O (l)
3Zn (s) + 8HNO3 (aq) → 3Zn(NO3)2 (aq) + 2NO (g) + 4H2O (l)
The concentration of copper(II) ions in the resulting solution is then determined from a calibration curve, which is plotted by measuring the light absorbance of standard solutions.
You may find the following chart and diagram helpful.
Copper(II) ion solutions are blue. Suggest, giving your reason, a suitable wavelength of light for the analysis.
[2]
orange is opposite blue «in the colour wheel»
OR
the complementary colour «blue» is seen/transmitted ✔
585–647 «nm would be absorbed» ✔
Accept any value or range within 550–680 «nm» for M2.
