Water, acidified with sulfuric acid, is decomposed by electrolysis - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2019 - Paper 1

The data from Figure 6 indicates that the volume of hydrogen produced increases steadily over time, while the volume of oxygen produced increases at a slower rate. The results suggest that the ratio of hydrogen to oxygen produced is approximately 2:1, aligning with the stoichiometry of the water decomposition reaction (2H₂O → 2H₂ + O₂). This implies that for every 2 volumes of hydrogen produced, 1 volume of oxygen is created.

C lead and bromine.

Calcium nitrate is soluble in water, dissociating into calcium ions (Ca²⁺) and nitrate ions (NO₃⁻), allowing it to conduct electricity. In contrast, calcium carbonate is not soluble in water, meaning it does not dissociate into ions and thus cannot conduct electricity. The movement of ions is essential for electrolysis, which is why calcium nitrate behaves as an electrolyte, while calcium carbonate does not.

1. The sizes of both the anode and the cathode change because copper ions from the anode dissolve into the electrolyte and deposit onto the cathode, causing the anode to decrease in size and the cathode to increase.

2. A solid appears directly beneath the anode due to the plating of impurities that do not dissolve, collecting as a solid residue.

3. The colour of the copper sulfate solution remains unchanged because the concentration of copper ions in the solution is maintained; as copper dissolves from the anode, it is immediately redeposited onto the cathode.