Question

When acetic and \[{K_4}Fe{(CN)_6}\] is added to a copper salt a chocolate precipitate is obtained from the compound.
A. Copper cyanide
B. Copper ferrocyanide
C. Basic copper sulphate
D. Basic copper cyanide

Answer 1

Hint: Precipitation reaction is a reaction where two compounds in its aqueous form react with each other to form an insoluble compound. This insoluble compound is known as a precipitate.

Complete Step by Step Solution:
The chemical name of\[{K_4}Fe{(CN)_6}\]is potassium ferrocyanide.
It is given that acetic acid and \[{K_4}Fe{(CN)_6}\] are added to a copper salt a chocolate precipitate is obtained from the compound.

The reaction takes place in a two-step, in the first step the salt of copper reacts with acetic acid to form copper nitrate as the main product.

The reaction taking place between copper salt and acetic acid is shown below:
\[[Cu{(N{H_3})_4}]{(N{O_3})_2} + 4C{H_3}COOH \to Cu{(N{O_3})_2} + 4C{H_3}COON{H_4}\]
In the above reaction, one mole of tetraamine copper(II) dinitrate reacts with four moles of acetic acid to form one mole of copper nitrate and four moles of ammonium acetate.

In the second step, the copper nitrate formed reacts with potassium ferrocyanide to form a chocolate precipitate.
The reaction taking place between copper nitrate and potassium ferrocyanide is shown below.
\[2Cu{(N{O_3})_2} + {K_4}[Fe{(CN)_6}] \to C{u_2}[Fe{(CN)_6}] + 4KN{O_3}\]

In the above reaction, two mol of copper nitrate react with one mole of potassium ferrocyanide to form one mole of copper(II) ferrocyanide and four mol of potassium nitrate.
Therefore, the correct option is B.

Note: Precipitation reaction is also known as double displacement reaction or ionic reaction. A double displacement reaction is the one where one ion present in a compound displaces another ion of another compound and vice versa.