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Water, acidified with sulfuric acid, is decomposed by electrolysis - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2019 - Paper 1
Question 6
Water, acidified with sulfuric acid, is decomposed by electrolysis. (i) A sample of hydrogen is mixed with air and ignited. State what would happen. (ii) Througho... show full transcript
Worked Solution & Example Answer:Water, acidified with sulfuric acid, is decomposed by electrolysis - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2019 - Paper 1
Step 1
A sample of hydrogen is mixed with air and ignited. State what would happen.
Answer
When a sample of hydrogen mixed with air is ignited, it will react with oxygen present in the air, leading to combustion. This reaction produces water vapor and is typically explosive, resulting in a loud bang and the formation of steam.
Step 2
Describe, using the data in Figure 6, what the results show about the volumes of hydrogen and of oxygen produced in this experiment.
Answer
The data in Figure 6 demonstrates that the volume of hydrogen produced increases at a steady rate. For every 2 cm³ increase in hydrogen, the volume of oxygen produced increases by 1 cm³, which reflects the stoichiometric ratio of the decomposition of water into hydrogen and oxygen, confirming the reaction:
ightarrow 2H_2 + O_2$$ This indicates that the volume of hydrogen is always twice that of oxygen during the electrolysis process.Step 4
Explain, in terms of solubility and movement of ions, this difference in behaviour.
Answer
Calcium nitrate dissolves in water, dissociating into calcium ext{Ca}^{2+} and nitrate ext{NO}_3^{-} ions, making the solution conductive and allowing it to act as an electrolyte. In contrast, calcium carbonate has low solubility in water and does not dissociate significantly into ions, thus not conducting electricity and failing to function as an electrolyte.
Step 5
Explain all three observations.
Answer
- The sizes of both the anode and the cathode change because during electrolysis, copper ions from the impure copper anode lose their charge and deposit on the cathode as pure copper, increasing its size while decreasing the size of the anode.
- A solid appears directly beneath the anode as impurities that are not soluble in the electrolyte accumulate there as the copper ions are oxidized and leave their initial copper structure.
- The colour of the copper sulfate solution does not change because the concentration of copper sulfate remains constant; the amount of copper deposited on the cathode is equal to the amount of copper oxidized at the anode, leading to no net change in the solution's colour.