Exam

JEE Main

Year

2025

Date

28 January

Shift

Morning Shift

Subject

Chemistry

Chapter

Ionic Equilibrium

JEE Main 2025 · 28 January · Morning Shift · Chemistry · Ionic Equilibrium

A weak acid HA has degree of dissociation x . Which option gives...

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

Step-by-step solution

$$\begin{aligned} & \mathrm{K}_{\mathrm{a}}=\frac{\left[\mathrm{H}^{+}\right](\mathrm{x})}{\mathrm{C}(1-\mathrm{x})} \\ & {\left[\mathrm{H}^{+}\right]=\mathrm{K}_{\mathrm{a}} \frac{(1-\mathrm{x})}{\mathrm{x}}} \\ & \log \mathrm{H}^{+}=\log \mathrm{K}_{\mathrm{a}}+\log \left(\frac{1-\mathrm{x}}{\mathrm{x}}\right) \\ & -\log \mathrm{H}^{+}=-\log \mathrm{K}_{\mathrm{a}}-\log \frac{1-\mathrm{x}}{\mathrm{x}} \\ & \mathrm{pH}=\mathrm{pK}_{\mathrm{a}}-\log \frac{1-\mathrm{x}}{\mathrm{x}} \\ & \mathrm{pH}-\mathrm{pK}_{\mathrm{a}}=\log \frac{\mathrm{x}}{1-\mathrm{x}}\end{aligned}$$