Question

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 1

3

Answer 2

Solution:

• For Fe³⁺: On adding K₄[Fe(CN)₆], a deep blue precipitate (Prussian blue) forms.
• For Cu²⁺: It reacts with K₄[Fe(CN)₆] to give a blue precipitate of copper ferrocyanide.
• For Zn²⁺: A white precipitate of zinc ferrocyanide is formed.
• For Ba²⁺, Ca²⁺, NH₄⁺, and Mg²⁺: No characteristic precipitate is produced with K₄[Fe(CN)₆].

Thus, the number of cations giving a characteristic precipitate is 3.

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Explanation (minimal):

Fe³⁺, Cu²⁺, and Zn²⁺ form characteristic precipitates with K₄[Fe(CN)₆]. The remaining ions do not.