91- 6303239042
Formula / Core Reaction:
$$4\text{Cl}^- + \text{Cr}_2\text{O}_7^{2-} + 6\text{H}^+ \text{(conc.)} \xrightarrow{\Delta} 2\text{CrO}_2\text{Cl}_2 \uparrow \text{(Deep Red)} + 3\text{H}_2\text{O}$$
$$\text{CrO}_2\text{Cl}_2 + 4\text{NaOH} \rightarrow \text{Na}_2\text{CrO}_4 \text{ (Yellow Solution)} + 2\text{NaCl} + 2\text{H}_2\text{O}$$
$$\text{Na}_2\text{CrO}_4 + (\text{CH}_3\text{COO})_2\text{Pb} \rightarrow \text{PbCrO}_4 \downarrow \text{(Yellow)}$$
Concept: Heating a chloride salt with potassium dichromate ($$\text{K}_2\text{Cr}_2\text{O}_7$$) and concentrated $$\text{H}_2\text{SO}_4$$ evolves volatile reddish-brown vapors of chromyl chloride ($$\text{CrO}_2\text{Cl}_2$$). Absorbing these in $$\text{NaOH}$$ gives yellow sodium chromate, confirmed by yellow $$\text{PbCrO}_4$$ precipitate.
Notation / Key Observation:
- $$\text{CrO}_2\text{Cl}_2$$: Chromyl chloride gas (Deep reddish-orange vapors);
- $$\text{PbCrO}_4$$: Lead chromate (Yellow precipitate);
- Note: Heavy metal chlorides ($$\text{HgCl}_2, \text{AgCl}, \text{PbCl}_2$$) do not show this test.
