Qualitative Salt Analysis : Sulphide ($$\text{S}^{2-}$$)

Formula / Core Reaction:

$$\text{S}^{2-} + 2\text{H}^+ \rightarrow \text{H}_2\text{S} \uparrow$$

$$\text{Pb(CH}_3\text{COO})_2 + \text{H}_2\text{S} \rightarrow \text{PbS} \downarrow \text{(Black)} + 2\text{CH}_3\text{COOH}$$

Concept: Acidification of sulfide salts with dilute acids liberates hydrogen sulfide ($$\text{H}_2\text{S}$$) gas, recognized by its rotten-egg odor and its ability to turn lead acetate paper silvery black due to $$\text{PbS}$$ formation.

Notation / Key Observation:

• $$\text{H}_2\text{S}$$: Gas with rotten egg smell;
• $$\text{PbS}$$: Lead sulfide black shiny precipitate.