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This question is about electrolysis - Edexcel - GCSE Chemistry - Question 5 - 2021 - Paper 1
Question 5
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 car... show full transcript
Worked Solution & Example Answer:This question is about electrolysis - Edexcel - GCSE Chemistry - Question 5 - 2021 - Paper 1
Step 1
A hydrogen and oxygen
Answer
The electrolysis of molten potassium bromide produces hydrogen and bromine at the electrodes. At the cathode, bromide ions (Br⁻) are discharged, releasing bromine gas (Br₂), while at the anode, potassium ions (K⁺) are discharged, producing hydrogen gas (H₂). Therefore, the correct answer is:
- A: hydrogen and bromine.
Step 2
Explain this difference.
Answer
Zinc chloride (ZnCl₂) dissolves in water to give Zn²⁺ and Cl⁻ ions, which can be discharged during electrolysis, allowing the substance to conduct electricity. In contrast, zinc carbonate (ZnCO₃) does not dissolve to give ions that can be discharged; therefore, it cannot undergo electrolysis. Thus, it is the solubility and the presence of free ions that facilitate the electrolysis of zinc chloride but not zinc carbonate.
Step 3
Step 4
Explain how this gas is formed at the cathode.
Answer
At the cathode, positively charged hydrogen ions (H⁺) are attracted to the negatively charged electrode. These hydrogen ions gain electrons and are reduced to form hydrogen gas:
ightarrow H_2$$ This reaction is what produces the hydrogen gas that can be observed bubbling at the cathode.