A student passes an electric current through molten lead(II) bromide using two carbon rods, X and Y, as shown in Fig. 1.1. Fig. 1.1 (a) Name the process tak...
Question 1 Report
A student passes an electric current through molten lead(II) bromide using two carbon rods, X and Y, as shown in Fig. 1.1.
Fig. 1.1
(a) Name the process taking place in the cell. [1]
(b) State the name given to electrode Y. [1]
(c) Name the product formed at electrode X. [1]
(d) Name the product formed at electrode Y. [1]
(e) Solid lead(II) bromide does not conduct electricity, but molten lead(II) bromide does. Explain why. [1]
Answer Details
This question is about the electrolysis of a molten ionic compound. In Fig. 1.1 electrode X is joined to the positive terminal and electrode Y to the negative terminal, so X is the anode and Y is the cathode. Lead(II) bromide, PbBr2, splits into Pb2+ and Br- ions that move to opposite electrodes.
(a) The process is electrolysis [1]: using electricity to break down a compound.
(b) Electrode Y is connected to the negative terminal, so it is the cathode [1].
(c) At electrode X (the positive anode) the bromide ions are discharged, so the product is bromine [1].
(d) At electrode Y (the negative cathode) the lead ions are discharged, so the product is lead [1].
(e) Solid lead(II) bromide does not conduct because its ions are fixed in the lattice, but when molten the ions are free to move to the electrodes and carry the charge, so it conducts and is decomposed [1].
Exam tip: for conduction you need charged particles that can move. Metals conduct with free electrons; molten or aqueous ionic compounds conduct with free-moving ions. Positive ions (Pb2+) go to the cathode, negative ions (Br-) go to the anode.
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