Among the following cations, the number of cations which will give characteristic precipitate in their identification tests with \(\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) is : \(\mathrm{Cu}^{2+}, \mathrm{Fe}^{3+}, \mathrm{Ba}^{2+}, \mathrm{Ca}^{2+}, \mathrm{NH}_{4}^{+}, \mathrm{Mg}^{2+}, \mathrm{Zn}^{2+}\)

JEE Main · 2025 · 24 Jan 2025 · Shift 1 · Practical and Analytical Chemistry

Among the following cations, the number of cations which will give characteristic precipitate in their identification tests with

K_{4} [Fe (CN)_{6}]

is :

Cu^{2 +}, Fe^{3 +}, Ba^{2 +}, Ca^{2 +}, NH_{4}^{+}, Mg^{2 +}, Zn^{2 +}

Answer: 3

Potassium ferrocyanide

K_{4} [Fe (CN)_{6}]

gives characteristic coloured precipitates with only a few cations.

C u^{2 +}

gives a reddish-brown precipitate

C u_{2} [Fe (CN)_{6}]

F e^{3 +}

gives the deep-blue Prussian-blue precipitate

F e_{4} [Fe (CN)_{6}]_{3}

, and

Z n^{2 +}

gives a white precipitate. The remaining ions do not react characteristically:

B a^{2 +}

C a^{2 +}

and

M g^{2 +}

form no characteristic precipitate with ferrocyanide, and

N H_{4}^{+}

gives none either. Hence three cations give a characteristic precipitate:

C u^{2 +}

F e^{3 +}

and

Z n^{2 +}

JEE Main · 2025 · 24 Jan 2025 · Shift 1 · Integer answer