Q113CP - Chemistry: Molecular Nature Of Matter And Change

Question

Question: For the compound $\left[\mathrm{Co}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]\mathbf{Cl}$, give:

(a) The coordination number of the metal ion

(b) The oxidation number of the central metal ion

(c) The number of individual ions per formula unit

(d) The moles of AgCl that precipitate immediately when 1 mol of compound is dissolved in water and treated with ${\mathbf{AgNO}}_{\mathbf{3}}$

Step-by-Step Solution

Answer

a) Coordination number is 6

b) Oxidation number of Co is 3+

c) Two individual ions.

d) 1 mol of  AgCl precipitates.

Step 1: Given data

The given compound is $\mathrm{Co}\left[{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]\mathrm{Cl}$

Step 2: Concept Introduction

The coordination number is the number of ligands directly attached to the central metal ions in a coordination compound. These ligands can be ions, atoms, or molecules. The most common coordination number is 6, but it is also not rare to see 2 and 4 as coordination numbers.

Step 3: Solution

a) We can see that there are 4 ligands bonded with a central metal ion (-en is bidentate), so the coordination number of  Co is six.

 

b) Cl has an oxidation number 1-  and en is a neutral ligand, so the oxidation number of Co is  3+.

 

c) There are two individual ions in this formula unit. They are:

$\mathrm{Co}{\left[{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]}^{+}$ and ${\mathrm{Cl}}^{-}$

d) When 1 mol of this compound is dissolved in water and treated with ${\mathrm{AgNO}}_3$, 1 mole of AgCl  precipitates because 1 counter ion ${\mathrm{Cl}}^{-}$ that is outside the brackets easily dissolves in water.