Question

Which of the following is the strongest base? ($K_b$ values at $25{}^{0}C$)

• A. Fluoride ion: $K_b=1.4\times {10}^{-11}$
• B. Ammonia : $K_b=1.8\times {10}^{-5}$
• C. Hydrazine : $K_b=9.5\times {10}^{-7}$
• D. Aniline : $K_b=4.3\times {10}^{-10}$

Answer 1

The correct option is B Ammonia : $K_b=1.8\times {10}^{-5}$

$Kb$ is the base dissociation constant. The base dissociation constant is a measure of how completely a base dissociates into its component ions in water.
A large $K_b$ value indicates that the base is strong. As $p{K}_b=-log\left[K_b\right]$ So , a lower $p{K}_b$ value indicates a stronger base. Ammonia has highest $Kb$ value, $K_b=1.8\times {10}^{-5}$ among all and hence is the strongest base.