Question

In a complex $CoC{l_3}.5N{H_3}$, one chloride ion satisfies both primary and secondary valences of cobalt.
A.True
B.False

Answer 1

Hint: This question can be solved from the knowledge of the oxidation state of the metal ion and the knowledge of primary and secondary valencies. Primary valency refers to the oxidation state of metal and secondary valency is the coordination number.

Complete step by step answer:
In the complex $CoC{l_3}.5N{H_3}$, the oxidation state of cobalt is $ + 3$ and hence to satisfy the charge it attracts the chloride ions. The primary valence is that which is required to satisfy the charge on the metal ion while the secondary valence is the one in which the central metal atom accepts electron pairs in the d-orbitals forming coordination bond with the ligands and hence the secondary charge is fulfilled.
The oxidation number of cobalt in the compound being $ + 3$ , is a ${d^6}$ complex and hence it has 6 electrons in the valence shell. So can take up 4 more electrons in the d subshell while 2 more in the 4s-subshell.
Hence a total of 6 electrons it can accept without hybridization, but after ${d^2}s{p^3}$ hybridization its secondary valence increases to 12. From the 5 ammonia molecules it gets 10 electrons while the last pair of electrons is supplied by the chloride anion. Hence the statement that, “In a complex $CoC{l_3}.5N{H_3}$, one chloride ion satisfies both primary and secondary valences of cobalt” is true.

Hence option A is correct.

Note:
The transition metal ions show different types of hybridization, one among them is the ${d^2}s{p^3}$ while the other one is the $s{p^3}{d^2}$ hybridization. The difference between both is that in the first one 3d, 4s and 4p orbitals are involved while in the second one 4s, 4p, and 4d orbitals are involved.