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6-2.Equilibrium-II (Ionic Equilibrium)
medium
નિર્બળ એસિડમાં હાઇડ્રોજન આયનની સાંદ્રતા વિયોજન અચળાંક ${K_a}$ અને સાંદ્રતા $c$ લગભગ ..... સમાન છે
A
$\sqrt {{K_a}c} $
B
$c/{K_a}$
C
${K_a}c$
D
$\sqrt {{K_a}/c} $
(AIPMT-1989)
Solution
Given- $K_a$ and $c$
To find $-\left[H^{+}\right]=$?
$\quad\quad\quad\quad HA \rightleftharpoons H ^{+}+ A ^{-}$
$t=0 \quad\quad c \quad\quad\quad0\quad \quad 0$
$t=t_1 \quad c-x \quad\quad x \quad\quad x$
For very weak acid $\Rightarrow x\,<<<,1$
$K_a =\frac{\left[H^{+}\right]\left[A^{-}\right]}{[H A]}$
$=\frac{x \times x}{c-x}$
where,$K_a =\text { Dissociation censtent }$
$c =[H A]$
$x =H^{+} \text {concentration }$
As $\quad x\,<<<\,1$ so $c-x \approx c$
$\therefore k_a =\frac{x^2}{c}$
$\Rightarrow x=\sqrt{k_a C}$
Standard 11
Chemistry
