A museum conservator is restoring brass name plates from an old ship. Each plate is given a protective copper coating using the circuit shown in Fig. 1. The...
Question 1 Report
A museum conservator is restoring brass name plates from an old ship. Each plate is given a protective copper coating using the circuit shown in Fig. 1. The beaker contains copper sulfate solution. Before the power supply is switched on, the conservator cleans the brass plate so that grease does not stop the coating sticking. During the reaction, copper atoms from one electrode enter the solution as ions and copper is deposited on the brass plate.
Fig. 1 Circuit for coating a brass plate with copper
(a) Name the process taking place in the beaker. [1]
(b) Use Fig. 1 to state which electrode, P or Q, is the cathode. [1]
(c) Describe what happens to the mass of brass plate Q during the reaction. [1]
(d) Complete the half-equation for the reaction at plate Q.
Cu2+ + ............ → Cu [2]
(e) Describe what happens to the mass of copper sheet P. [2]
(f) Suggest why the copper sulfate solution can remain blue if the process is continued for a long time. [2]
(g) Give two reasons why the conservator cleans the brass plate before electroplating it. [2]
Answer Details
Electroplating deposits a metal layer by reduction at the negative electrode.
- (a) The process is electroplating. [1]
- (b) Q is connected to the negative terminal, so Q is the cathode. [1]
- (c) Brass plate Q increases in mass because copper is deposited on it. [1]
- (d) \(\text{Cu}^{2+}+2e^-\rightarrow\text{Cu}\). The missing term is \(2e^-\), and the completed balanced half-equation is required. [2]
- (e) Copper sheet P decreases in mass. Copper atoms lose electrons, forming \(\text{Cu}^{2+}\) ions that enter the solution. [2]
- (f) \(\text{Cu}^{2+}\) ions are removed at Q, but they are replaced as copper dissolves from P. The concentration of blue \(\text{Cu}^{2+}\) ions can therefore remain similar. [2]
- (g) Cleaning removes grease or dirt, helps the copper adhere, gives a more even coating, and prevents bare patches. Any two. [2]
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