The hydrogen ion concentration in a weak acid | vedclass

Name: Exam Paper Generator | JEE NEET Paper Generator | Vedclass
Brand: Vedclass
Rating: 5 (35 reviews)

Question

(A) For a weak acid $HA$ dissociating as $HA \rightleftharpoons H^{+} + A^{-}$,the dissociation constant is given by $K_a = \frac{[H^{+}][A^{-}]}{[HA]

Vedclass · Accepted Answer

$\sqrt{K_a c}$

Vedclass · Answer

(A) For a weak acid $HA$ dissociating as $HA ightleftharpoons H^{+} + A^{-}$,the dissociation constant is given by $K_a = \frac{[H^{+}][A^{-}]}{[HA]}$.Let the initial concentration be $c$ and the degree of dissociation be $\alpha$.Then $[H^{+}] = c\alpha$,$[A^{-}] = c\alpha$,and $[HA] = c(1-\alpha)$.$K_a = \frac{(c\alpha)(c\alpha)}{c(1-\alpha)} = \frac{c\alpha^2}{1-\alpha}$.Since the acid is weak,$\alpha Thus,$K_a \approx c\alpha^2$,which gives $\alpha = \sqrt{K_a/c}$.Therefore,$[H^{+}] = c\alpha = c 	imes \sqrt{K_a/c} = \sqrt{K_a c}$.

The hydrogen ion concentration in a weak acid of dissociation constant $K_a$ and concentration $c$ is nearly equal to:

Similar Questions

The dissociation constant of a base $BOH$ at $25^{\circ} C$ is $1.0 \times 10^{-12}$. The concentration of $OH^{-}$ in a $0.01 \ M$ aqueous solution is .......

The ionisation constant of acetic acid is $1.8 \times 10^{-5}$. The concentration at which it will be dissociated to $2\%$,is (in $M$)

Find $pH$ of $5 \times 10^{-3} \ M$ $H_2CO_3$ solution having $10\%$ dissociation.

Which of the following compounds has the maximum $K_{a}$ value?

The $pH$ of two equimolar weak acids are $3.0$ and $5.0$ respectively. Their relative strength is

Vedclass Test Series

Exam Paper Generator

Online Exam Module