This question is about electrolysis - Edexcel - GCSE Chemistry Combined Science - Question 3 - 2021 - Paper 1
Question 3
This question is about electrolysis.
(a) A sample of molten potassium bromide is electrolysed.
What are the two products formed?
(b) Zinc chloride and zinc carbona... show full transcript
Worked Solution & Example Answer:This question is about electrolysis - Edexcel - GCSE Chemistry Combined Science - Question 3 - 2021 - Paper 1
Step 1
What are the two products formed?
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Answer
The two products formed during the electrolysis of molten potassium bromide are potassium and bromine. In this process, potassium ions (K⁺) move to the cathode where they gain electrons to form potassium metal, while bromide ions (Br⁻) move to the anode and lose electrons, forming bromine gas.
Step 2
Explain this difference.
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Answer
Zinc chloride mixed with water can be electrolysed because it dissolves to give free ions in solution, allowing for the movement of current. In contrast, zinc carbonate is insoluble in water and does not dissociate into ions, which prohibits the flow of electric current and thus prevents electrolysis from occurring.
Step 3
Identify this gas.
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Answer
The gas identified in the electrolysis of sodium chloride solution that produces a squeaky pop when ignited is hydrogen.
Step 4
Explain how this gas is formed at the cathode.
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Answer
At the cathode during the electrolysis of sodium chloride solution, water molecules are reduced. The electrolysis results in the formation of hydrogen gas as follows:
2H2O(l)+2e−→H2(g)+2OH−(aq)
Thus, hydrogen gas is produced by the reduction of water.
