Question

The Alsatian-Swiss chemist Alfred Werner pioneered the field of coordination chemistry in the late nineteenth century. At that time, a number of compounds of cobalt (III) chloride with ammonia were known, with general formula $CoC{l}_3.xN{H}_3$ $x=3to6$
Treatment of these compounds with aqueous HCl acid did not remove the ammonia. However, treatment of the compounds with excess of $AgN{O}_3$ at 273 K gave white precipitate of AgCl in varying ratio depending on the structure. Also each complex had electrical conductivity of varying nature.

There is no reaction of the compound with aqueous HCl indicating that there is no free $N{H}_3$. Thus, $N{H}_3$ ligand is bonded to cobalt(III) by________ .

• A. Primary valency.
• B. Secondary valency.
• C. Both of these.
• D. None of these.

Answer 1

Answer: (B)

Secondary valency.

Option (B) is correct.

Thus, $N{H}_3$ ligand is bonded to cobalt$\left(III\right)$ by secondary valency. Ammonia is present inside the coordination sphere and does not ionises while chloride ions present outside the sphere reacts with $AgN{O}_3$

$\left[Co\right(N{H}_3{)}_{5}Cl]C{l}_2+AgN{O}_3⟶[Co\left(N{H}_3{)}_{5}Cl\right](N{O}_3{)}_2+AgC{l}_2$