Question 18N.3.sl.TZ0.b
| Date | November 2018 | Marks available | [Maximum mark: 2] | Reference code | 18N.3.sl.TZ0.b |
| Level | sl | 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.
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.