Tin (II) Sulfide Precipitate

The best way to ensure complete precipitation of tin(II) sulfide from a saturated solution of hydrogen sulfide is to...
the answer is add a strong base. but I'm not clear on why this the right answer, can anyone explain?

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...de (SnS), the sulfide ion must be present, so the hydrogen sulfide must dissociate completely. This does not happen in neutral solution because ...