Question

What is the decreasing order of strength of the bases
$O{H}^{-}$,$N{H}_2^{-}$,$HC\equiv C^{-}$ and $C{H}_{3}C{H}_2^{-}$ ?

• A. $C{H}_{3}C{H}_2^{-}$ > $N{H}_2^{-}$ > $HC\equiv C^{-}$ > $O{H}^{-}$
• B. $HC\equiv C^{-}$ > $C{H}_{3}C{H}_2^{-}$ > $N{H}_2^{-}$ > $O{H}^{-}$
• C. $O{H}^{-}$ > $N{H}_2^{-}$ > $HC\equiv C^{-}$ > $C{H}_{3}C{H}_2^{-}$
• D. $N{H}_2^{-}$ > $HC\equiv C^{-}$ > $O{H}^{-}$ > $C{H}_{3}C{H}_2^{-}$

Answer 1

Answer: (A)

$C{H}_{3}C{H}_2^{-}$ > $N{H}_2^{-}$ > $HC\equiv C^{-}$ > $O{H}^{-}$

Answer:-

The conjugate base of a strong acid is weaker while the conjugate base of a weak acid is stronger.

Hence the correct order of strength of bases is $\to$

${C{H}_3-C{H}_2}^{-}>{N{H}_2}^{-}>{HC\equiv C}^{-}>{OH}^{-}$

here, $C{H}_{3}C{H}_3^{-}$ is the conjugate base for ethane and $HC\equiv C^{-}$ is the conjugate base for ethyne. SInce ethyne has more s-character thane ethane, it is more acidic. Thus, the conjugate base of ethyne will be less basic than the conjugate base of ethane.