The electrolysis of other molten substances
5 marks · HardA molten ionic compound XY is electrolysed using inert electrodes.
State which element is produced at the cathode. Explain your answer.
State which element is produced at the anode. Explain your answer.
Give one reason why these predictions are valid only for molten binary ionic compounds, not aqueous ones.
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) Element X (the metal), because cations are attracted to the cathode where they gain electrons (are reduced). · must show Names X or 'metal', Explains positive ions migrate to cathode and are reduced
(b) Element Y (the non-metal), because anions are attracted to the anode where they lose electrons (are oxidised). · must show Names Y or 'non-metal', Explains negative ions migrate to anode and are oxidised
(c) In aqueous solutions, water can be discharged at the electrodes or compete with the ions present. · must show Mentions water is present and can be discharged
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States correctly that X (metal) is formed at the cathode
M1 (a) · 1 mark · Explains that cations/positive ions move to cathode and are reduced (gain electrons)
B2 (b) · 1 mark · States correctly that Y (non-metal) is formed at the anode
M2 (b) · 1 mark · Explains that anions/negative ions move to anode and are oxidised (lose electrons)
B3 (c) · 1 mark · Gives a valid reason: Water can be discharged at the electrodes or competes in aqueous solution
Worked solution
a) X is formed at the cathode. In a molten binary ionic compound, the metal forms positive ions (X^+ or X^{n+}) which are attracted to the cathode, where they gain electrons (reduction) to form the metal X.
b) Y is formed at the anode. The non-metal forms negative ions (Y^- or Y^{n-}) which are attracted to the anode, where they lose electrons (oxidation) to form the non-metal element Y.
c) In aqueous solutions, water is present and can be discharged at either electrode, so the products may differ.