Question

$K_a$ for formic acid and acetic acid are $1.7\times 10^{-4}$ and $1.1\times 10^{-5}$ respectively. The relative strength of acid is ____.

Answer 1

Answer: 4

Relative strength of weak acids

$=\sqrt{\left(\frac{K_{a_1}}{K_{a_2}}\times \frac{C_1}{C_2}\right)}$

Assume $C_1$ and $C_2$ are same (Although not given)

$\therefore$ Relative strength $=\sqrt{\left(\frac{K_{a_1}}{K_{a_2}}\right)}=\sqrt{\left(\frac{1.7\times 10^{-4}}{1.1\times 10^{-5}}\right)}$

Relative strength for $HCOOH$ to $C{H}_{3}COOH=4:1$