Question Constellation Sign up for free AQA · GCSE · Chemistry · Higher
Carbon electrodes during electrolysis
Figure 10 shows the electrolysis cell used to extract aluminium from aluminium oxide.
Explain what happens to the positive carbon electrodes during the extraction of aluminium from aluminium oxide.
Write your answer first. You can study the marking guidance whenever you need it.
Study the marking See what earns credit and compare it with a full-mark answer.
Marking points
- 1 States that oxygen is produced at the positive electrodes.
- 2 Explains that oxygen reacts with carbon to form carbon dioxide.
- 3 Concludes that the carbon electrodes are consumed and must be replaced.
Full-mark answer
Oxygen is produced at the positive electrodes. It reacts with the carbon to form carbon dioxide, so the carbon electrodes are gradually used up and must be continually replaced.
Why this answer loses marks
Oxygen forms at the positive electrode.
This gives only the first link; it must connect oxygen reacting with carbon, carbon dioxide formation, and the electrode being used up.