Formulae for ionic compounds

2 marks · Normal

State the formulae for the following ionic compounds:

(a)

potassium sulfide

[1 mark]

(b)

aluminium nitrate

[1 mark]

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(a) K2S

(b) Al(NO3)3

Common mistakes: forgetting to balance charges; missing brackets for nitrate

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Marking points

A1 (a) · 1 mark · Correct formula for potassium sulfide: K2S.

A2 (b) · 1 mark · Correct formula for aluminium nitrate: Al(NO3)3.

Worked solution

a) Potassium forms K+, sulfide forms S2-. Need two K+ for one S2− to balance charges: K2S b) Aluminium forms Al3+, nitrate is NO3−. Need three NO3− for one Al3+: Al(NO3)3