During the electrolysis of water the volume of gas at each electrode was measured over time. time / min volume at electrode A / cm3 volume at electrode B / ...
Question 1 Report
During the electrolysis of water the volume of gas at each electrode was measured over time.
| time / min | volume at electrode A / cm3 | volume at electrode B / cm3 |
|---|---|---|
| 1 | 4 | 2 |
| 2 | 8 | 4 |
| 3 | 12 | 6 |
Answer Details
Positive ions travel to the negative electrode, and in acidified water the ion available there is H+, which gains electrons to give hydrogen: 2H+ + 2e- → H2. So the gas at electrode A is hydrogen.
The volumes confirm it. At each time the reading at A is exactly double the reading at B: 4 and 2, then 8 and 4, then 12 and 6, so the ratio is a constant 2 : 1. That is precisely what 2H2O → 2H2 + O2 predicts, since equal volumes of gases contain equal numbers of molecules under the same conditions.
Quoting 1 : 2 reverses the order asked for, and calling the cathode gas oxygen swaps the electrodes. Check the direction of the ratio against the wording before writing it down.
Download The App On Google Playstore
Everything you need to excel in your exams
