The electrical conductivity of ionic substances

5 marks · Hard

Lead(II) nitrate is an ionic compound. It can be either solid, molten, or dissolved in water.

(a)

State whether lead(II) nitrate conducts electricity in each of the following states:

State	Does it conduct? (Yes/No)
Solid
Molten
Aqueous solution

[2 marks]

(b)

Explain, in terms of ions, why lead(II) nitrate behaves in this way in these states.

[3 marks]

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) — · must show Solid: No, Molten: Yes, Aqueous solution: Yes

(b) — · must show Solid: ions fixed/not free to move, so cannot conduct, Molten/Aqueous: ions are free to move, so conduct electricity, Correct reference to movement of ions in molten and aqueous state

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · Solid: Correctly states 'No'.

B2 (a) · 1 mark · Molten and aqueous: Both correctly identified as 'Yes'.

M1 (b) · 1 mark · States that in the solid, ions are fixed and cannot move.

M2 (b) · 1 mark · States that in molten and aqueous states ions are free to move.

A1 (b) · 1 mark · Links the movement of ions to the conduction of electricity in molten/aqueous states.

Worked solution

Conductivity of lead(II) nitrate in different states
State	Does it conduct? (Yes/No)
Solid	No
Molten	Yes
Aqueous solution	Yes

In the solid state, the ions in lead(II) nitrate are held rigidly in a lattice and cannot move, so the substance does not conduct electricity.

When molten or dissolved in water, the ionic lattice is broken and the ions are free to move. These moving ions can carry an electric current, so the substance conducts electricity in these states.