Question

Consider the coordination compound, $[Co{{(N{{H}_{3}})}_{6}}]C{{l}_{3}}$. In the formation of this complex, the species which acts as the Lewis base is:
A. $C{{l}^{-}}$
B. $C{{o}^{3+}}$
C. $N{{H}_{3}}$
D. ${{[Co{{(N{{H}_{3}})}_{6}}]}^{3+}}$

Answer 1

Hint: A Lewis base functions by donating a pair of electrons to a Lewis acid in order to form a Lewis adduct. In our question, $N{{H}_{3}}$ contains lone pairs which are available for donation.

Complete step by step solution:
In order to solve the question you need to have a clear understanding of Lewis acids and Lewis bases. Lewis acids are those substances which have the capability of accepting an electron and Lewis bases are those, which have the ability to donate an electron and form an adduct. Lewis acids do so because they have an incomplete octet of electrons i.e their outer shell is not filled. So it will try to get it filled to attain stability. On the other hand, Lewis bases are those substances that have a filled outer shell. These electrons/electron pairs might not be available in bonding, but can form a dative bond with the Lewis bases, in order to form an adduct and attain stability. In our question we can observe that $C{{o}^{3+}}$ has an unfilled octet, whereas, $N{{H}_{3}}$ have a lone pair of electrons. So it can form an adduct.

Hence, we can conclude that the Lewis base in the given coordination compounds is $N{{H}_{3}}$, the answer being option C.

Note: You may need to remember some important Lewis acids and bases, for getting a time advantage during the exam. It is to be remembered that the molecules where the central atom has more than 8 electrons in the valence shell, are capable to accept electrons and generally are Lewis acids.