Electrolysis
5 marks · EasyThe table shows some properties of substances at room temperature.
| Substance | Type of Bonding | Solid? (yes/no) | Molten? (yes/no) | In solution? (yes/no) | Conducts electricity? (yes/no) |
|---|---|---|---|---|---|
| Copper | Metallic | Yes | No | No | Yes |
| Sodium chloride (NaCl) | Ionic | Yes | Yes | Yes | No |
| Methane (CH4) | Covalent | Yes | No | No | No |
State one reason why copper conducts electricity as a solid.
Give one reason why solid sodium chloride does not conduct electricity.
Explain how sodium chloride can be made to conduct electricity.
You pass electricity through molten sodium chloride using a simple cell and two inert (carbon) electrodes.
In this experiment, what is the name given to the liquid sodium chloride?
State the name given to the positive electrode and the negative electrode.
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(i)) Copper conducts electricity as a solid because it has free-moving (delocalised) electrons. · must show Reference to delocalised electrons free to move
(a(ii)) Solid sodium chloride does not conduct electricity because its ions are not free to move—they are held in fixed positions in a lattice. · must show Ions fixed/not free to move
(a(iii)) Sodium chloride conducts electricity when molten or in solution, because the ions are then free to move. · must show Ions free to move when molten or dissolved
(b(i)) Electrolyte · must show Correct use of 'electrolyte' terminology
(b(ii)) Positive electrode: anode; Negative electrode: cathode · must show Anode and cathode labelled to correct polarity
Common mistakes: Confusing free electrons and ions for charge carriers in compounds; Mixing up anode and cathode
Show mark scheme and worked solution
Marking points
B1 (a(i)) · 1 mark · Identifies delocalised/free-moving electrons in copper as the reason for conductivity.
B1 (a(ii)) · 1 mark · States that ions are fixed in a lattice/not free to move in solid NaCl.
B1 (a(iii)) · 1 mark · Explains that ions are free to move when NaCl is molten/in solution, so it conducts.
B1 (b(i)) · 1 mark · Correctly names the liquid as 'electrolyte'.
B1 (b(ii)) · 1 mark · Correctly names the positive electrode as anode and the negative as cathode.
Worked solution
a(i) Copper conducts as a solid because its delocalised electrons are free to move.
a(ii) Solid sodium chloride does not conduct because the ions are in fixed positions and cannot move.
a(iii) Sodium chloride conducts when molten or dissolved, because the ions are now free to move.
b(i) The liquid sodium chloride is the electrolyte.
b(ii) The positive electrode is called the anode; the negative electrode is the cathode.