Passing electricity through compounds: electrolysis
4 marks · NormalA student recorded observations of three substances to analyse their ability to conduct electricity in different states.
| Substance | Solid | Molten | Aqueous |
|---|---|---|---|
| Sodium chloride | no | yes | yes |
| Sugar | no | no | no |
| Potassium nitrate | no | yes | yes |
Which of these substances are ionic compounds? Explain your answer using the data.
Suggest why sugar does not conduct electricity in any state.
Which substance is an example of a covalent compound?
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.
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(a) Sodium chloride and potassium nitrate are ionic because they conduct electricity when molten and in aqueous solution, but not as solids. · must show Identification of correct compounds, Justification based on conduction data
(b) Sugar does not produce ions in any state. · must show Absence of ions
(c) Sugar · must show Sugar
Common mistakes: Misidentifying sugar as ionic; not linking conduction to ion movement.
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Identifies sodium chloride and potassium nitrate as ionic compounds based on their conductivity.
M1 (a) · 1 mark · Explains that these substances conduct when molten and in solution, but not as solids.
B1 (b) · 1 mark · Correctly states that sugar does not conduct because it does not produce ions.
B1 (c) · 1 mark · Identifies sugar as a covalent compound.
Worked solution
a. Sodium chloride and potassium nitrate are ionic compounds because they only conduct electricity when molten or in aqueous solution, not as solids. This means their ions are only free to move in these states.
b. Sugar does not conduct because it is a covalent compound; it does not form ions in any state.
c. Sugar is a covalent compound.