4.7 Required practical: making a soluble salt
5 exam questions worth 8 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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Why is excess copper oxide added to the sulfuric acid?
Choose one answer.
Correct Not quite: the answer is To make sure all the acid reacts
Mark scheme
B
Model answer
B: excess base ensures all the acid reacts.
Explain how the student knows when the copper oxide is in excess.
Mark scheme
- black solid remains / no more dissolves (1)
Model answer
Some black copper oxide stays undissolved in the beaker however much it is stirred.
Explain why the mixture is filtered.
Mark scheme
- to remove the excess / unreacted copper oxide (1)
- because it is insoluble (1)
Model answer
Filtering removes the unreacted copper oxide, which is an insoluble solid, leaving copper sulfate solution.
Suggest why the copper sulfate solution is heated over a water bath rather than directly with a Bunsen burner.
Mark scheme
- gentler / more controlled heating (1)
- prevents spitting / prevents the solution boiling dry / stops the salt decomposing (1)
Model answer
A water bath heats gently and evenly, so the solution does not spit or boil dry and the crystals are not damaged.
Name the acid and the insoluble base you would use to make zinc chloride crystals.
Mark scheme
- hydrochloric acid (1)
- zinc oxide / zinc carbonate (1)
Model answer
Use hydrochloric acid with excess zinc oxide (or zinc carbonate).
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