The electrical conductivity of ionic substances
4 marks · NormalThe table below shows the electrical conductivity of three ionic compounds in solid and molten states.
| Substance | Conducts when solid? | Conducts when molten? |
|---|---|---|
| Potassium iodide | ||
| Magnesium oxide | ||
| Sodium nitrate |
Complete the table by indicating Yes or No for each box. Then, explain your reasoning for one of your answers.
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
Must show: All three: No for solid, Yes for molten
Common mistakes: Putting Yes for solid; Mixing up molten and aqueous
Show mark scheme and worked solution
Marking points
A1 · 1 mark · States 'No' for all substances in solid state.
A2 · 1 mark · States 'Yes' for all substances in molten state.
E1 · 2 marks · Explains for one substance that in solid state, ions are fixed and cannot move (1 mark), and in molten state, ions can move and conduct (1 mark).
Worked solution
| Substance | Conducts when solid? | Conducts when molten? |
|---|---|---|
| Potassium iodide | No | Yes |
| Magnesium oxide | No | Yes |
| Sodium nitrate | No | Yes |
Example explanation: In solid magnesium oxide, ions are fixed in the lattice and cannot move, so it does not conduct. When molten, the ions can move and carry charge, so it conducts.