Question

A monomeric compound of Co gives the following data on analysis:
$Co - 21.24\% ,Cl - 12.81\% ,{H_2}O - 6.53\% ,N{H_3} - 24.77\% ,SO_4^{2 - } - 34.65\%$
Give the structural formula of the compound if the given compound gives no precipitate with lunar caustic$\left( {AgN{O_3}} \right)$.

Answer 1

To answer this question, you must recall the isomerism shown by coordination compounds. Coordination compounds are addition compounds which do not lose their identity in an aqueous solution and do not furnish all the ions present in the compound.

Complete step by step answer:
First we determine the structure of the coordination compound using the given data about the mass percentage of various species present in the compound. We are given the mass percentage of each species. Dividing it by the molecular masses we find the mole percentage of the compounds.

Entity	Mass percentage	Mole percentage	Mole ratio
Cobalt	$21.24{\text{ }}\%$	$\dfrac{{21.24}}{{59}} = 0.36$	1
Chlorine	$12.81{\text{ }}\%$	$\dfrac{{12.81}}{{35.5}} = 0.36$	1
Water	$6.53{\text{ }}\%$	$\dfrac{{6.53}}{{18}} = 0.36$	1
Ammonia	$24.77{\text{ }}\%$	$\dfrac{{24.77}}{{17}} = 1.45$	4
Sulphate	$34.65{\text{ }}\%$	$\dfrac{{34.65}}{{96}} = 0.36$	1

Now we know the mole ratio of the constituents. Considering them as the actual number of moles of the compound, we form the structural formula of the compound. Of the given ligand molecules, two can act as ions and satisfy the secondary valency of cobalt ion, either chlorine or sulphate ion. Since it is given that the compound does not form a precipitate with $AgN{O_3}$, hence we can conclude that chlorine is not the anionic species. The precipitate mentioned is that of $AgCl$.
The structural formula of the given coordination compound can be written as, $\left[ {Co{{\left( {N{H_3}} \right)}_4}\left( {{H_2}O} \right)Cl} \right]S{O_4}$.
Note:
The compounds in which a central metal atom or ion is linked to a number of ligands, which may be either neutral or ionic Lewis bases, that carry an extra pair of electrons are known as coordination compounds. The bond formed between the central metal atom or ion and the ligand is a coordinate bond, i.e., the bond is formed by the donation of a lone pair of electrons from the ligand to the central metal ion/ atom.