Question

Which compound does not form a precipitate when reacted with sodium hydroxide?

Responses

NaCl

uppercase N lowercase a uppercase C lowercase l

Fe(NO3)3

uppercase F lowercase e open parenthesis uppercase N O subscript 3 end subscript close parenthesis subscript 3 end subscript

Cu(NO3)2

uppercase C lowercase u open parenthesis uppercase N O subscript 3 end subscript close parenthesis subscript 2 end subscript

FeSO4

Answer 1

NaCl

Reason: NaCl is soluble and neither Na+ nor Cl− form an insoluble hydroxide with OH−, so no precipitate forms. By contrast:

- Fe(NO3)3 + 3 OH− → Fe(OH)3(s) (brown precipitate)
- Cu(NO3)2 + 2 OH− → Cu(OH)2(s) (blue precipitate)
- FeSO4 + 2 OH− → Fe(OH)2(s) (green/dirty precipitate, oxidizes to brown on air)