Question

What is the decreasing order of strength of the following bases?
(A) $O{H^ - },N{H_2}^ - ,HC \equiv {C^ - }$ and $C{H_3} - C{H_2}^ - $
(B) $C{H_3} - C{H_2}^ - > N{H_2}^ - > H - C \equiv {C^ - } > O{H^ - }$
(C) $H - C \equiv {C^ - } > C{H_3} - C{H_2}^ - > N{H_2}^ - > O{H^ - }$
(D) $O{H^ - } > N{H_2}^ - > H - C \equiv {C^ - } > C{H_3} - C{H_2}^ - $
(E) $N{H_2}^ - > H - C \equiv {C^ - } > O{H^ - } > C{H_3} - C{H_2}^ - $

Answer 1

Hint: In such questions, we simply use the concept of converting these bases into acids. Then we compare their acidic strengths i.e. which acid is stronger or which acid is weaker. Whatever the answer you receive, reverse the order of that answer.

Complete step by step solution:
> Whenever we want to convert a conjugate base and conjugate acid, we add the positive ion into it. For example-
- First conjugate base given by the question is $O{H^ - }$. We will add ${H^ + }$ to convert it into conjugate acid. We will get-
$ \Rightarrow O{H^ - } + {H^ + } \rightleftharpoons {H_2}O$
- Second conjugate base given by the question is $N{H_2}^ - $. We will add ${H^ + }$ to convert it into conjugate acid. We will get-
$ \Rightarrow N{H_2}^ - + {H^ + } \rightleftharpoons N{H_3}$
- Third conjugate base given by the question is $HC \equiv {C^ - }$. We will add ${H^ + }$ to convert it into conjugate acid. We will get-
$ \Rightarrow HC \equiv {C^ - } + {H^ + } \rightleftharpoons CH \equiv CH$
- Fourth conjugate base given by the question is $C{H_3} - C{H_2}^ - $. We will add ${H^ + }$ to convert it into conjugate acid. We will get-
$ \Rightarrow C{H_3} - C{H_2}^ - + {H^ + } \rightleftharpoons C{H_3} - C{H_3}$
> Now, we will compare the acidic strengths of the above-mentioned acids.
As we can see, the most acidic strength is of ${H_2}O$.
> Then comes $CH \equiv CH$. As we can see, the hybridization is this acid is sp. Which means its acidic percentage increases as the more the percentage of sp, the more the acidic strength. Thus, this comes after ${H_2}O$.
> Then comes $N{H_3}$. This is because hydrogen is linked with nitrogen which is electronegative in nature.
> Then we have $C{H_3} - C{H_3}$.
So, we get the order of acidic strength as-
$ \Rightarrow {H_2}O > CH \equiv CH > N{H_3} > C{H_3} - C{H_3}$
This is the order of acidic strength. We will reverse this order to get our required answer.
So, the order of basic strength will be-
$ \Rightarrow C{H_3} - C{H_2}^ - > N{H_2}^ - > H - C \equiv {C^ - } > O{H^ - }$

Hence, we can say that option A is the correct option.

Note: The strength of an acid refers to the pattern of dissociation of proton, H+, and an anion, A− of an acid symbolized by the chemical formulation HA. With the exception of the most concentrated forms, a strong acid solution is essentially complete.