Question 18N.3.sl.TZ0.a
| Date | November 2018 | Marks available | [Maximum mark: 1] | Reference code | 18N.3.sl.TZ0.a |
| Level | sl | 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.
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”.
