Question 18N.3.hl.TZ0.1a
| Date | November 2018 | Marks available | [Maximum mark: 1] | Reference code | 18N.3.hl.TZ0.1a |
| Level | hl | Paper | 3 | Time zone | TZ0 |
| Command term | Outline | Question number | a | 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.
Outline why the initial reaction should be carried out under a fume hood.
[1]
NO2/NO/NOx/HNO3/gas is poisonous/toxic/irritant ✔
Accept formula or name.
Accept “HNO3 is corrosive” OR “poisonous/toxic gases produced”.
Accept “reaction is harmful/hazardous”.
