Question 19M.2.sl.TZ1.c
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.sl.TZ1.c |
| Level | sl | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | c | Adapted from | N/A |
This question is about iron.
An iron nail and a copper nail are inserted into a lemon.
Explain why a potential is detected when the nails are connected through a voltmeter.
[2]
lemon juice is the electrolyte
OR
lemon juice allows flow of ions
OR
each nail/metal forms a half-cell with the lemon juice [✔]
Note: Accept “lemon juice acts as a salt bridge”.
Any one of:
iron is higher than copper in the activity series
OR
each half-cell/metal has a different redox/electrode potential [✔]
Note: Accept “iron is more reactive than copper”.
iron is oxidized
OR
Fe → Fe2+ + 2e–
OR
Fe → Fe3+ + 3e−
OR
iron is anode/negative electrode of cell [✔]
copper is cathode/positive electrode of cell
OR
reduction occurs at the cathode
OR
2H+ + 2e− → H2 [✔]
electrons flow from iron to copper [✔]
Notes:
Accept “lemon juice acts as a salt bridge”.
Accept “iron is more reactive than copper”.
Very few students gained the 2 marks available for explaining the potential generated in the lemon as they didn’t realise it was the lemon that acted as the electrolyte and allowed ions to flow. Some were able to gain a mark for explaining that electrons moved from iron to copper as iron is more reactive.
