The electrolysis of molten compounds
3 marks · NormalElectrolysis is carried out on molten magnesium chloride (MgCl2) using inert electrodes.
Predict the product formed at the anode. Explain your answer.
Write a balanced half-equation for the reaction at the cathode.
Explain why molten magnesium chloride conducts electricity, but solid magnesium chloride does not.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Chlorine gas (Cl2) is formed at the anode because chloride ions lose electrons there (are oxidised).
(b) Mg^{2+} + 2e^- → Mg
(c) Molten MgCl2 conducts electricity because the ions are free to move. In the solid, the ions are fixed in place (in a lattice) and cannot move, so it does not conduct electricity.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States chlorine gas (Cl2) is formed at the anode and gives a reason (chloride ions lose electrons/are oxidised).
B1 (b) · 1 mark · Correct half-equation for Mg^{2+} at the cathode: Mg^{2+} + 2e^- → Mg
B1 (c) · 1 mark · Explains that molten MgCl2 conducts as ions are free to move, but solid does not conduct as ions are fixed in a lattice.
Worked solution
a) The product at the anode is chlorine gas (Cl2) because chloride ions (Cl^-) lose electrons (are oxidised) at the anode.
b) The half-equation at the cathode is:
c) Molten magnesium chloride conducts electricity because ions are free to move and carry charge. In the solid, ions are locked in a lattice and cannot move, so it does not conduct.