What would happen with non-electrolytes?
5 marks · HardA student investigates the electrical conductivity of three white solids: compound A, compound B and compound C. The student tests each substance (i) as a solid, (ii) after dissolving it in water, and (iii) after melting it. The observations are recorded below:
| Substance | Solid | Aqueous solution | Molten |
|---|---|---|---|
| Compound A | Does not conduct | Does not conduct | Does not conduct |
| Compound B | Does not conduct | Conducts | Conducts |
| Compound C | Does not conduct | Does not conduct | Conducts |
For each compound (A, B and C), state whether it is ionic, covalent (non-electrolyte), or another type. Give a reason for each answer.
Suggest a familiar example of a substance that would behave in the same way as compound A.
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) A: Covalent (non-electrolyte) – does not conduct in any state. B: Ionic (soluble in water) – does not conduct as solid, but conducts in aqueous and molten states. C: Ionic (insoluble in water) – does not conduct as solid or aqueous, but conducts when molten. · must show A correctly identified for all three; reason for each
(b) Sugar (sucrose) · must show Identifies a common covalent non-electrolyte
Common mistakes: Incorrect assignment of ionic/covalent for each compound
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly identifies compound A as a covalent (non-electrolyte) with valid reason
B2 (a) · 1 mark · Correctly identifies compound B as ionic (soluble) with valid reason
B3 (a) · 1 mark · Correctly identifies compound C as ionic (insoluble) with valid reason
B4 (a) · 1 mark · Gives clear explanations for all three choices (may be awarded for coherence if descriptions are correct but short for one on three)
B5 (b) · 1 mark · Suggests an appropriate example for compound A (e.g., sugar/sucrose/glucose)
Worked solution
For each compound:
Compound A: Does not conduct in any state – this means it is a covalent compound (non-electrolyte), since it does not produce ions in solution or molten.
Compound B: Does not conduct as a solid, but does conduct as a solution and molten – typical of an ionic compound that is soluble in water.
Compound C: Conducts only when molten – an ionic compound that is insoluble in water, so no ions present when in solution.
Example for A: Sucrose (sugar) is a common non-electrolyte that matches these properties.