Chemistry · Ionic Equilibrium

JEE Main 2025 — 28 January, Morning Shift — Question 30

A weak acid HA has degree of dissociation $x$ . Which option gives the correct expression of $\mathrm{pH}=\mathrm{pK}_{\mathrm{a}}$ ) ?

Answer: D

$\quad \mathrm{HA} \rightleftharpoons \mathrm{H}^{\oplus}+\mathrm{A}^{\Theta}$

$\mathrm{t}=0 \quad \mathrm{a}$

$\mathrm{t}=\mathrm{t} \quad \mathrm{a}(1-\mathrm{x}) \quad \mathrm{ax} \quad \mathrm{ax}$

$\mathrm{K}_{\mathrm{a}}=(\mathrm{ax}) \frac{(\mathrm{x})}{1-\mathrm{x}} ;\left[\mathrm{H}^{+}\right]=\mathrm{ax}$

$-\log \left(K_{a}\right)=-\log (a x)-\log \left(\frac{x}{1-x}\right)$

$\mathrm{pKa}=\mathrm{pH}-\log \left(\frac{\mathrm{x}}{1-\mathrm{x}}\right)$

$\mathrm{pH}-\mathrm{pKa}=\log \left(\frac{\mathrm{x}}{1-\mathrm{x}}\right)$

Answer key and solution verified before publishing.

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