Passing electricity through compounds: electrolysis
3 marks · NormalExplain why covalent molecular compounds such as methane () do not conduct electricity, but aqueous ammonia () can conduct electricity. Refer to the presence or absence of ions in your answer.
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Methane does not contain ions, so there are no charged particles to carry an electric current. Aqueous ammonia forms ions ( and ) when dissolved in water, so it can conduct electricity because these ions can move.
Must show: Methane does not conduct: absence of ions, Aqueous ammonia conducts: presence of ions
Also accept: Ammonia solution contains free-moving ions; methane does not.; Methane is covalent with no ions; ammonia in water produces ions.
Common mistakes: Suggesting methane has ions; not explaining formation of and .
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Marking points
M1 · 1 mark · Recognises that for a substance to conduct electricity, ions must be present and free to move.
B1 · 1 mark · States that methane () does not contain ions, so cannot conduct electricity.
B1 · 1 mark · Explains that aqueous ammonia produces ions ( and ), so can conduct electricity.
Worked solution
Methane () is a covalent molecular compound, so it has no ions and all electrons are shared in covalent bonds. This means there are no charged particles to carry current. Aqueous ammonia reacts with water to form ions: . These ions are free to move, allowing the solution to conduct electricity.