Qualitative Analysis: Group 6 Cation ($$\text{Mg}^{2+}$$)

Formula / Core Reaction:

$$\text{Mg}^{2+} + \text{NH}_4\text{OH} + \text{Na}_2\text{HPO}_4 \rightarrow \text{Mg(NH}_4)\text{PO}_4 \downarrow \text{(White)} + 2\text{Na}^+ + \text{H}_2\text{O}$$

Concept: Magnesium remains in solution after filtering Groups 1 to 5. Addition of disodium hydrogen phosphate in alkaline ammonium medium precipitates magnesium ammonium phosphate.

Notation / Key Observation:

• Group Reagent: Disodium hydrogen phosphate ($$\text{Na}_2\text{HPO}_4$$) + $$\text{NH}_4\text{OH}$$;
• $$\text{Mg(NH}_4)\text{PO}_4$$: Magnesium ammonium phosphate (White crystalline precipitate).