First slide

Qualitative analysis

Question

Why $A l^{3 +}, F e^{+ 3}, C r^{+ 3}$ are grouped at one place together for qualitative analysis

Moderate

A

as their carbonates are insoluble in NH₃
B

as their hydroxide are insoluble in NH₃
C

as their sulphides are insoluble in acid
D

as their sulphides are soluble in acid

Solution

${Fe}^{3 +} + {NH}_{4} OH + {NH}_{4} Cl \to Fe {(OH)}_{3}$
Which is insoluble in NH₃
${Al}^{3 +} + {NH}_{4} OH + {NH}_{4} Cl \to Al {(OH)}_{3}$
Which is insoluble in NH₃
${Cr}^{3 +} + {NH}_{4} OH + {NH}_{4} Cl \to Cr {(OH)}_{3}$
Which is insoluble inNH₃
As the solubility product of their hydroxides is less.

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