91Ó°ÊÓ

${\mathbf{K}}_a$is known as the acid dissociation constant and its value indicates the relative strength of the acid. ${\mathbf{pK}}_a$is defined as the negative logarithm (base $10$) of ${\mathbf{K}}_a$. Mathematically, ${\text{pK}}_{\text{a}}{\text{=-logK}}_{\text{a}}$.value of strong acids is usually zero or even negative while the value of weaker acids are greater than$4$ .

The strength of an acid or base is given by its ${\text{pK}}_{\text{a}}$value. The smaller localid="1662465510222" ${\mathbf{\text{pK}}}_{\mathbf{\text{a}}}$value means stronger is the acid while the larger localid="1662465496640" ${\mathbf{\text{pK}}}_{\mathbf{\text{a}}}$value means stronger is the base.

$\begin{array}{l}{\text{pK}}_{\text{a}}{\text{ â¶Ä‰o´Ú â¶Ä‰â¶Ä‰N±á}}_{\text{4}}\text{°ä±ô â¶Ä‰= â¶Ä‰9.26}\\ {\text{pK}}_{\text{a}}\text{ â¶Ä‰o´Ú â¶Ä‰â¶Ä‰H°ä±·â€‰â¶Ä‰= â¶Ä‰9.22}\\ {\text{pK}}_{\text{a}}{\text{ â¶Ä‰o´Ú â¶Ä‰â¶Ä‰C±á}}_{\text{3}}\text{°ä°¿°¿±á â¶Ä‰= â¶Ä‰4.74}\\ {\text{pK}}_{\text{a}}\text{ â¶Ä‰o´Ú â¶Ä‰â¶Ä‰H°ä°¿°¿±á â¶Ä‰= â¶Ä‰3.76}\\ {\text{pK}}_{\text{a}}{\text{ â¶Ä‰o´Ú â¶Ä‰â¶Ä‰H}}_{\text{2}}{\text{SO}}_{\text{4}}\text{ â¶Ä‰= â¶Ä‰-5}\\ {\text{pK}}_{\text{a}}\text{ â¶Ä‰o´Ú â¶Ä‰â¶Ä‰HI  =  -11}\\ {\text{pK}}_{\text{a}}\text{ â¶Ä‰o´Ú â¶Ä‰â¶Ä‰HBr  =  -9}\end{array}$