Qualitative Salt Analysis: Group 1 Cation ($$\text{Pb}^{2+}$$)

Formula / Core Reaction:

$$\text{Pb}^{2+} + 2\text{HCl} \rightarrow \text{PbCl}_2 \downarrow \text{(White)}$$

$$\text{PbCl}_2 + 2\text{KI} \xrightarrow{\Delta, \text{ cool}} \text{PbI}_2 \downarrow \text{(Golden Yellow "Golden Spangles")}$$

Concept: Group 1 cations precipitate as insoluble chlorides using dilute $$\text{HCl}$$. $$\text{PbCl}_2$$ dissolves in hot water and reprecipitates upon cooling with $$\text{KI}$$ as brilliant golden yellow crystalline flakes.

Notation / Key Observation:

• Group Reagent: Dilute $$\text{HCl}$$;
• $$\text{PbCl}_2$$: White precipitate soluble in hot water;
• $$\text{PbI}_2$$: Lead iodide (Golden yellow precipitate / Golden Spangles test).