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NEET 2023
Exam
NEET
Year
2023
Subject
Chemistry
Chapter
Ionic Equilibrium

NEET 2023 · Chemistry · Ionic Equilibrium

For a weak acid HA , the percentage of dissociation is nearly 1 \%...

For a weak acid HA\mathrm{HA}, the percentage of dissociation is nearly 1%1 \% at equilibrium. If the concentration of acid is 0.1 mol L−10.1 \mathrm{~mol} \mathrm{~L}^{-1}, then the correct option for its Ka\mathrm{K}_{\mathrm{a}} at the same temperature is

Options

  1. A1×10−51 \times 10^{-5}
  2. B1×10−31 \times 10^{-3}
  3. C1×10−41 \times 10^{-4}
  4. D1×10−61 \times 10^{-6}

Correct answer

A. 1×10−51 \times 10^{-5}

Step-by-step solution

HA⇌H++A−At t=0C− At eq. C−CαCαCαK=[H+][A−][HA]=(Cα)(Cα)C(1−α)=Cα21−α=C2(∵α is very small )=0.1(0.01)2=1×10−5\begin{aligned} & \mathrm{HA} \rightleftharpoons \mathrm{H}^{+}+\mathrm{A}^{-} \\ & \text{At } \mathrm{t}=0 \quad \mathrm{C} \quad- \\ & \text{ At eq. } \mathrm{C}-\mathrm{C} \alpha \quad \mathrm{C} \alpha \quad \mathrm{C} \alpha \\ & \mathrm{K}=\frac{\left[\mathrm{H}^{+}\right]\left[\mathrm{A}^{-}\right]}{[\mathrm{HA}]}=\frac{(\mathrm{C} \alpha)(\mathrm{C} \alpha)}{\mathrm{C}(1-\alpha)}=\frac{\mathrm{C} \alpha^2}{1-\alpha}=\mathrm{C}^2 \quad(\because \alpha \text{ is very small }) \\ & =0.1(0.01)^2=1 \times 10^{-5} \\ & \end{aligned}
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