Question 18N.3.hl.TZ0.b
| Date | November 2018 | Marks available | [Maximum mark: 2] | Reference code | 18N.3.hl.TZ0.b |
| Level | hl | Paper | 3 | Time zone | TZ0 |
| Command term | Deduce | Question number | b | 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.
Deduce the equation for the relationship between absorbance and concentration.
[2]
Slope (gradient):
40 ✔
Equation:
absorbance = 40 × concentration
OR
y = 40x ✔
Accept any correct relationship for slope such as .
Award [2] if equation in M2 is correct.