Question

What is the value of $p{K}_b\left(C{H}_{3}CO{O}^{-}\right)if{\lambda }_m^{\infty }=390and{\lambda }_m=7.8$ for $0.04M$ of a $C{H}_{3}COOH$ solution at ${25}^{\circ }C$?

• A. 9.3
• B. 9.2
• C. 4.7
• D. 4.8

Answer 1

The correct option is B 9.2

$\alpha =\frac{{\lambda }_m}{{\lambda }_m}=\frac{7.8}{390}=0.02$

$K_a\left(C{H}_{3}COOH\right)=C{\alpha }^2=0.04\times 4\times {10}^{-4}=16\times {10}^{-6}$

$p{K}_a=4.8$

$p{K}_a+p{K}_b=14$

so $p{K}_b=9.2$

Hence, option B is correct.