Question

On the basis of the following observations made with aqueous solutions, assign secondary valences to metals in the following compounds:

Formula	Moles of a AgCl precipitated per mole of the compounds with excess $AgN{O_3}$
$PdC{l_2}.4N{H_3}$	2
$NiC{l_2}.6{H_2}O$	2
$PtC{l_4}.2HCl$	0
$CoC{l_3}.4N{H_3}$	1
$PtC{l_2}.2N{H_3}$	0

Answer 1

To answer this question, you must recall the Werner’s theory. It is used to find the secondary valency. Secondary valency is the coordination number of the central metal atom or ion in a given coordination compound.

Complete step by step solution:
Werner’s theory states that a metal has two types of valencies in a coordination compound, namely primary valency and secondary valency. Primary valency refers to the oxidation state of the central metal ion while the secondary valency refers to the coordination number of the metal ion.
In the question, we are given the number of moles of $AgCl$ precipitated. This gives us the primary valency of the compound. Subtracting it from the total valency of the metal ion we get the secondary valency.
$PdC{l_2}.4N{H_3}$ : 2 moles of $AgCl$ are precipitated. Thus the secondary valency is 4.
$NiC{l_2}.6{H_2}O$ : 2 moles of $AgCl$ are precipitated. Thus the secondary valency is 6.
$PtC{l_4}.2HCl$ : 0 moles of $AgCl$ are precipitated. Thus the secondary valency is 6.
$CoC{l_3}.4N{H_3}$ : 1 moles of $AgCl$ are precipitated. Thus the secondary valency is 6.
$PtC{l_2}.2N{H_3}$ : 0 moles of $AgCl$ are precipitated. Thus the secondary valency is 4.

Note:
Coordination compounds are a type of additional compound.
Coordination compounds are the compounds in which a central metal atom is linked by coordination bond to a number of ligands, which may either be ions or neutral molecules, i.e. by donation of lone pairs by the ligands to the central metal atom. If this compound carries a positive or negative charge, it is called a complex ion. These complex ions are relatively stable and they do not lose their identity in aqueous solution like double salts.
Apart from coordination compounds, the other type of addition compounds are double salts. Unlike coordination compounds, double salts are stable only in crystalline state and lose their identity in solution form.