Question

What is the charge on ${[Ag{(CN)_2}]^ - }$ ?
A) $+ 1$
B) $- 1$
C) $+ 2$
D) $+ 3$

Answer 1

We know that ${[Ag{(CN)_2}]^ - }$ is a coordinate compound, in which cyanide acts as a monodentate ligand. The chemical name of ${[Ag{(CN)_2}]^ - }$ is Dicyanoargentate. The charge on $CN$ is $- 1$ . In presence of potassium ions, this complex form Potassium dicyanoargentate $\left( 1 \right)$

Complete step by step solution:
We know that silver cyanide is a chemical compound with a molecular formula $AgCN$ . Silver ion is represented by $Ag$ and cyanide ion is represented by $CN$ . This silver cyanide is precipitated in presence of sodium cyanide to a solution containing silver ions. This precipitate further dissolves when we add cyanide ions and form ${[Ag{(CN)_2}]^ - }$ . This complex has a linear structure and its name is Dicyanoargentate.
Now let's calculate the charge on this complex. Let the charge of $Ag$ being x. We know that the charge of $CN$ is $- 1$ . Substituting the values according to the molecular formula ${[Ag{(CN)_2}]^ - }$ we get
\eqalign{ & \Rightarrow x + 2 \times - 1 = - 1 \cr & \Rightarrow x = 1 \cr}
Thus the charge on the complex is $+ 1$ . Dicyanoargentate forms a coordinate compound. A coordinate compound is a compound in which a central atom, in this case, silver is surrounded by non-metal atoms, cyanide ions. Cyanide ions act as monodentate ligands. Cyanide ion is a monodentate ligand because it has only one co-ordination atom. In presence of potassium ions, this complex form Potassium dicyanoargentate $\left( 1 \right)$

Note: We should know what are coordinate bonds. It is also known as a dative bond. It is formed when the bonding electrons are shared by only one of the two atoms. It is a type of covalent bond. In ${[Ag{(CN)_2}]^ - }$ , cyanide ions supply electrons and form coordinate bonds with silver.