A weak acid HA has degree of dissociation . Which option gives the correct expression of ? [2025]

STUDY MATERIALS
COURSES
MORE
SUCCESS STORY
ADMISSION
STORE

Back

JEE ADVANCE

CLASS XI - XII
CRASH COURSE

CLASS XI - XII

CRASH COURSE

JEE MAIN

CLASS XI - XII
CRASH COURSE

CLASS XI - XII

CRASH COURSE

NEET

CLASS XI - XII
CRASH COURSE

CLASS XI - XII

CRASH COURSE

BITSAT

CLASS XI - XII

CLASS XI - XII

CBSE BOARD

CLASS IX

CLASS X

CLASS XI

CLASS XII

CLASS VI

CLASS VII

CLASS VIII

UP BOARD

CLASS IX
CLASS X
CLASS XI
CLASS XII

CLASS IX

CLASS X

CLASS XI

CLASS XII

CUET

CRASH COURSE

CRASH COURSE

Courses

CLASSROOM COURSES
ONLINE COURSES

ONLINE COURSES

More

Solution

Q.
A weak acid HA has degree of dissociation $x$ . Which option gives the correct expression of $(pH - p K_{a})$ [2025]

1 $\log (1 + 2 x)$

2 $0$

3 $\log (\frac{x}{1 - x})$

4 $\log (\frac{1 - x}{x})$

Ans.
(3)

$\begin{matrix} HA & ⇌ & H^{+} & + & A^{-} \\ (t=0) (moles) & a_{0} & 0 & 0 \\ (t=∞) (moles) & a (1 - x) & a_{0} x & a_{0} x \end{matrix}$

$K_{a} = \frac{[H^{+}] [A^{-}]}{[HA]} = \frac{[H^{+}] \times a_{0} x}{a_{0} (1 - x)}$

$K_{a} = \frac{[H^{+}] \times x}{(1 - x)}$

Taking $- \log$ on both sides

$- \log K_{a} = - \log (\frac{[H^{+}] \times x}{(1 - x)})$

$- \log K_{a} = - \log [H^{+}] - \log (\frac{x}{1 - x})$

$p K_{a} = pH - \log (\frac{x}{1 - x})$

$pH - p K_{a} = \log (\frac{x}{1 - x})$

Want Us to Email you About Special Offers & Updates?