Question

$PdC{l_2} \cdot 4N{H_3},PtC{l_2} \cdot 2N{H_3}$ and $CoC{l_3} \cdot 4N{H_3}$ reacts with excess of $AgN{O_3}$ individually and gave 2 mole of AgCl, zero moles of AgCl and 1 mole of AgCl respectively. Then identify the secondary valences of Pd, Pt and Co respectively.
(A) 6, 4, 7
(B) 4, 2, 4
(C) 2, 2, 3
(D) 4, 4, 6

Answer 1

If chlorine atom is present which forms an ionic bond, then one mole of that compound will react with one mole of $AgN{O_3}$ to give 1 mole of AgCl. Secondary valency of any metal atom in a complex is the number of ligands attached with the metal atom in the complex.

Complete Step-by-Step Solution:
We can see that three complexes are given to us here and we need to find the secondary valency of the metal atom in them. We will first know about secondary valency and then we will find its value for the given metals.
- Secondary valency of any metal atom in a complex is the number of ligands attached with the metal atom in the complex. We know that these ligands are attached with the metal atom by covalent coordinate bonds.
- We know that $AgN{O_3}$ reacts with chloride ions and gives AgCl. Silver nitrate does not react with the chlorine atoms which are forming coordinate covalent bonds.
- $PdC{l_2} \cdot 4N{H_3}$ gives 2 moles of AgCl when it reacts with silver nitrate. Thus, both chlorine atoms should not be attached with covalent coordinate bonds. That means that the total ligands attached with Pd is four because of four ammonia ligands. Thus, 4 is the secondary valency of Pd atom in $PdC{l_2} \cdot 4N{H_3}$.
- $PtC{l_2} \cdot 2N{H_3}$ does not give AgCl in its reaction with silver nitrate. This means that both the chlorine atoms and two ammonia molecules are bonded with covalent coordinate bonds. Thus, the secondary valency of Pt atom here is 2+2=4.
- $CoC{l_3} \cdot 4N{H_3}$ gives one mole of AgCl when allowed to react with silver nitrate. Thus, one chlorine atom should be bonded with ionic bond. That means two chlorine atoms and four ammonia molecules are bonded with Co metal by covalent coordinate bonds. So, the secondary valency of Co atom will be 2+4=6.
So, we can conclude that the secondary valency of Pd, Pt and Co atom is the given complex is 4, 4 and 6 respectively.

Therefore, the correct answer of the question is (D).

Note: Do not get confused between primary valency and secondary valency of the metal atom in the complex. Actually, the primary valency of the metal in a complex is the number of negative ions attached which are equivalent with the charge on the metal atom.