Why things conduct electricity
4 marks · NormalThe table shows the results from testing four substances for electrical conductivity:
| Substance | State | Conducts electricity? |
|---|---|---|
| Potassium bromide | Solid | No |
| Potassium bromide | Molten | Yes |
| Glucose | Solution in water | No |
| Potassium bromide | Solution in water | Yes |
Use the data to identify the substance(s) that conduct electricity and describe the conditions in which conduction occurs.
Suggest a reason why potassium bromide conducts electricity in its molten state and in aqueous solution, but not as a solid.
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) Potassium bromide conducts electricity when molten and in solution; glucose does not conduct.
(b) In molten or aqueous states, potassium bromide's ions are free to move and carry charge, but in the solid, the ions are held in place within the lattice and cannot move.
Common mistakes: Stating electrons carry charge in ionic compounds
Show mark scheme and worked solution
Marking points
A1 (a) · 1 mark · Correctly identifies potassium bromide as the conducting substance and the states where it conducts.
B1 (a) · 1 mark · Correctly states that glucose solution does not conduct.
M1 (b) · 1 mark · Explains ion movement in molten/aquous state allows conduction.
M2 (b) · 1 mark · Explains ions in the solid are not free to move.
Worked solution
a) Potassium bromide conducts electricity when molten and when dissolved in water. Glucose solution does not conduct.
b) In the molten or aqueous state, potassium bromide's ions are free to move and can carry charge, allowing it to conduct. In the solid, the ions are locked in the lattice and cannot move.