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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?
Answer
The two products formed when a sample of molten potassium bromide is electrolyzed are potassium and bromine. During the electrolysis process, the potassium ions are discharged at the cathode, forming potassium metal, while bromide ions are discharged at the anode, producing bromine gas.
Step 2
Explain this difference.
Answer
Zinc chloride is soluble in water, allowing it to dissociate into zinc ions and chloride ions. This means that the ions are free to move in solution, enabling the electrolysis process. In contrast, zinc carbonate is not soluble in water, so it does not dissociate into ions when mixed with water. As a result, there are no free-moving ions available for electrolysis in the zinc carbonate mixture.
Step 4
Explain how this gas is formed at the cathode.
Answer
Hydrogen gas is formed at the cathode through the reduction of hydrogen ions present in the solution. During the electrolysis of sodium chloride solution, water molecules are also present, which dissociate into hydrogen ions (H⁺) and hydroxide ions (OH⁻). At the cathode, the hydrogen ions gain electrons (reduction) to form hydrogen gas: