Question 18N.3.hl.TZ0.1d
| Date | November 2018 | Marks available | [Maximum mark: 3] | Reference code | 18N.3.hl.TZ0.1d |
| Level | hl | Paper | 3 | Time zone | TZ0 |
| Command term | Outline | Question number | d | 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 how a solution of 0.0100 mol dm−3 is obtained from a standard 1.000 mol dm−3 copper(II) sulfate solution, including two essential pieces of glassware you would need.
[3]
dilute 1.00 cm3 «of the standard solution with water» to 100 cm3
OR
dilute sample of standard solution «with water» 100 times ✔
«graduated/volumetric» pipette/pipet ✔
volumetric flask ✔
Accept any 1 : 100 ratio for M1.
Accept “mix 1 cm3 of the standard solution with 99 cm3 of water” for M1.
Do not accept “add 100 cm3 of water to 1.00 cm3 of standard solution” for M1.
Accept “burette/buret” for M2.
Accept “graduated/measuring flask” for M3 but not “graduated/measuring cylinder” or “conical/Erlenmeyer flask”.
