4.16 Required practical: electrolysis of aqueous solutions
5 exam questions worth 7 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Which result shows that oxygen has been collected?
Choose one answer.
Correct Not quite: the answer is A glowing splint relights
Mark scheme
C
Model answer
C: oxygen relights a glowing splint.
Explain why the electrodes must not touch each other.
Mark scheme
- it would cause a short circuit / current would not pass through the solution (1)
Model answer
If they touched, the current would flow straight between them (a short circuit) and the solution would not be electrolysed.
Describe what you would see at the cathode when copper sulfate solution is electrolysed with carbon electrodes.
Mark scheme
- pink-brown / orange-brown coating of copper (1)
Model answer
A pink-brown coating of copper forms on the cathode.
Give one safety precaution needed when electrolysing sodium chloride solution, and explain why.
Mark scheme
- well-ventilated room / small amounts / switch off quickly / eye protection (1)
- chlorine is toxic (1)
Model answer
Work in a well-ventilated room and switch off as soon as possible, because chlorine is toxic.
A student predicts that hydrogen forms at the cathode when sodium sulfate solution is electrolysed. Explain whether the prediction is correct.
Mark scheme
- correct (1)
- sodium is more reactive than hydrogen, so hydrogen forms (1)
Model answer
The prediction is correct: sodium is more reactive than hydrogen, so hydrogen gas is produced at the cathode.
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