DP Chemistry (first assessment 2025)
Question 22M.2.SL.TZ2.5a
| Date | May 2022 | Marks available | [Maximum mark: 2] | Reference code | 22M.2.SL.TZ2.5a |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Deduce | Question number | a | Adapted from | N/A |
a.
[Maximum mark: 2]
22M.2.SL.TZ2.5a
(a)
Deduce the half-equations for the reaction at each electrode.
[2]
Markscheme
Cathode (negative electrode):
Zn2+ + 2e− → Zn (l) ✔
Anode (positive electrode):
2Cl− → Cl2 (g) + 2e−
OR
Cl− → ½ Cl2 (g) + e− ✔
Examiners report
The half-equations were often incorrect. The average mark was 0.8 out of 2, and the correlation to high scoring candidates was strong as expected. Many candidates started the half-equations with the elements and gave the ions as products. We also saw some scripts with Cl instead of Cl2 as the product. Some of the candidates thought the zinc ion was Zn+ instead of Zn2+. Some candidates reversed the anode and cathode equations earning only 1 of the 2 marks.
Syllabus sections
Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.2—Electron transfer reactions » Reactivity 3.2.2—Half-equations separate the processes of oxidation and reduction, showing the loss or gain of electrons. Deduce redox half-equations and equations in acidic or neutral solutions.