The sodium fusion extract is acidified with acetic acid and lead acetate is added to it. A black precipitate of lead sulphide indicates the presence of sulphur.

What is the need for acidification of extract before adding lead acetate? Wouldn't Lead sulfide be formed if we add directly lead acetate? Can we use any other acid and its salt of lead?

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    $\begingroup$ The silver test for halides (using silver nitrate) requires the mixture to be acidified to remove carbonate because silver carbonate could precipitate and be confused for a silver halide. Lead carbonate is also insoluble in water, so maybe this is the reason for using acid here. $\endgroup$ – f'' Aug 14 '16 at 9:19
  • $\begingroup$ @f" But lead carbonate is not black whereas leadsulfide is black $\endgroup$ – JM97 Aug 14 '16 at 9:30
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    $\begingroup$ Still, it is better not to have any unnecessary side reactions with their precipitates that may obscure your vision. $\endgroup$ – Ivan Neretin Aug 25 '16 at 14:57

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