Question

Among the following acids which has the lowest $pK_a$ value ?

• A. $CH_3CH_2COOH$
• B. $(CH_3)_2CH??OOH$
• C. $HCOOH$
• D. $CH_3COOH$

Answer 1

Answer: (C)

$HCOOH$

Answer 2

Out of the given acids, strongest is $HCOOH$. (highest $K_a$ value) Since $pK_a = - log\, K_a$ Thus lowest $pK_a$ is of $HCOOH$.