Question 5
HA laboratory investigates the purity of an impure copper electrode using the apparatus shown.
The positive electrode loses 3.40 g and the negative electrode gains 3.18 g. All electrodes are washed and dried before weighing. Assume that only copper dissolves from the positive electrode, all dissolved copper is deposited on the negative electrode, and all insoluble impurities from the portion lost fall to the bottom of the container.
a.[2]
Write a balanced half-equation for the reaction at each electrode. Include electrons.
b.[3]
Calculate the percentage by mass of copper in the portion lost from the positive electrode. Give your answer to three significant figures.
c.[3]
The volume of solution remains constant. Explain why the concentration of copper(II) ions remains approximately constant during this experiment. Refer to both electrode reactions.
d.[2]
The experiment is repeated, but the negative electrode is weighed while still wet at the end. Explain how this would affect the calculated percentage purity.
4.2 Electrolytic processes Questions
52 exam-style questions on Edexcel GCSE Chemistry 4.2 Electrolytic processes, covering 4.2.1 Electrolytes and the process of electrolysis, 4.2.2 Products of electrolysis using inert electrodes, 4.2.3 Half equations, oxidation and reduction in electrolysis, and 4.2.4 Electrolysis of copper sulfate and purifying copper. Each one has a worked solution and a mark scheme showing where the marks go.