Fig. 1 shows a student using electrolysis to obtain copper from copper sulfate solution. The table records the mass of each electrode before and after a 20-...
Question 1 Report
Fig. 1 shows a student using electrolysis to obtain copper from copper sulfate solution. The table records the mass of each electrode before and after a 20-minute run. The student uses graphite electrodes because graphite is a conductor and does not react easily.
| electrode | mass before / g | mass after / g |
|---|---|---|
| negative graphite electrode | 4.20 | 4.38 |
| positive graphite electrode | 4.22 | 4.22 |
(a) Use Table 1 to give the mass increase of the negative electrode. [1]
(b) Name the metal deposited on the negative electrode. [1]
(c) What particle moves to the negative electrode from the solution? [1]
(d) Give one reason why graphite is used for the electrodes. [1]
(e) Suggest why the negative electrode gains mass. [1]
(f) Complete the formula for copper(II) ions: Cu____. [1]
Answer Details
(a) \(4.38 - 4.20 = 0.18\), so the mass increase is 0.18 g. [1]
(b) The metal deposited on the negative electrode is copper. [1]
(c) Copper ions, \(\mathrm{Cu^{2+}}\), move through the solution to the negative electrode. Positive ions are attracted to the negative electrode. [1]
(d) Graphite is used because it conducts electricity. It is also acceptable to state that it is unreactive. [1]
(e) The negative electrode gains mass because copper is deposited on it. Copper ions gain electrons and become copper atoms. [1]
(f) The ion formula is \(\mathrm{Cu^{2+}}\), so the missing charge is 2+. [1]
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