Molten lead(II) bromide, PbBr2, is electrolysed using two carbon electrodes as shown in Fig. 1.1. Carbon is inert and does not react during the electrolysis...
Question 1 Report
Molten lead(II) bromide, PbBr2, is electrolysed using two carbon electrodes as shown in Fig. 1.1. Carbon is inert and does not react during the electrolysis.
(a) State why solid lead(II) bromide must first be heated until it is molten before it will conduct electricity. [1]
(b) Name the product formed at electrode Y. [1]
(c) Name the product formed at electrode X. [1]
(d) Write the ionic half-equation, including state symbols, for the reaction at electrode Y. [2]
(e) State the name given to the electrode connected to the positive terminal of the power supply. [1]
Answer Details
This question is the electrolysis of molten lead(II) bromide with inert carbon electrodes. In the diagram electrode X is connected to the positive terminal (the anode) and electrode Y to the negative terminal (the cathode).
(a) In the solid the ions are locked in a fixed lattice and cannot move; melting frees the ions so they can move and carry the current, so it must be molten before it will conduct [1]. [1]
(b) At electrode Y (the negative cathode) the positive lead ions are discharged, so the product is lead (metal) [1]. [1]
(c) At electrode X (the positive anode) the negative bromide ions are discharged, so the product is bromine [1]. [1]
(d) Reaction at electrode Y (cathode), lead ions gaining electrons:
\[ \text{Pb}^{2+}(l) + 2e^{-} \rightarrow \text{Pb}(l) \]
correct species and balancing [1]; two electrons and state symbols correct [1]. [2]
(e) The electrode connected to the positive terminal of the power supply is the anode [1]. [1]
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