Question

The salt used for performing bead test in qualitative inorganic analysis is:

• A. K₂SO₄.Al₂(SO₄)₃.24H₂O
• B. FeSO₄.(NH₄)2SO₄.6H₂O
• C. Na(NH₄)HPO₄.4H₂O
• D. CaSO₄.2H₂O

Answer 1

The correct option is C

Na(NH₄)HPO₄.4H₂O

$Na\left(N{H}_4\right)HP{O}_4.4H_{2}O$ is called microcosmic salt. It is prepared by dissolving $N{a}_{2}P{O}_4$ and $N{H}_{4}Cl$. Like Borax, it is used for detecting coloured ions like $M{n}^{2+}$, $C{u}^{2+}$ etc. through bead test. Heating it gives sodium metaphosphate, which forms coloured beadswhen heated with coloured salts.

$Na\left(N{H}_4\right)HP{O}_4.4H_{2}O\to N{H}_3+H_{2}O+NaP{O}_3$

$CuS{O}_4\to CuO+S{O}_3$

$CuO+NaP{O}_3\to CuNaP{O}_4$ (blue bead)

Sodium Copper Orthophosphate