Why things conduct electricity
3 marks · EasyA student tests four different substances for electrical conductivity in different states. The results are shown below:
| Substance | State | Conducts electricity? |
|---|---|---|
| Lead bromide | Molten | Yes |
| Sucrose | Solid | No |
| Potassium nitrate | Aqueous solution | Yes |
| Silicon dioxide | Solid | No |
Identify which substance is a covalent compound and give evidence from the table for your answer.
State the common feature of all the substances that do conduct electricity in this test.
Suggest why silicon dioxide does not conduct electricity.
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)) Sucrose. It does not conduct electricity in solid form, which is expected for a covalent compound.
(a(ii)) They all have ions that are free to move.
(a(iii)) Silicon dioxide does not have free ions or electrons to carry charge.
Show mark scheme and worked solution
Marking points
A1 (a(i)) · 1 mark · Identifies sucrose as the covalent compound, with appropriate evidence from the table (does not conduct as solid).
A2 (a(ii)) · 1 mark · Recognises that all conducting substances have free-moving ions.
A3 (a(iii)) · 1 mark · Correctly explains that silicon dioxide lacks free ions or electrons.
Worked solution
i. Sucrose. It is covalent and does not conduct electricity in solid state.
ii. The substances that conduct electricity all have ions that are free to move.
iii. Silicon dioxide has no free ions or electrons.