Acid–base Equilibria

Question

The percent dissociation of a 1.0×10⁻³ M solution of a weak monoprotic acid (Ka = 1.0×10⁻⁵) is approximately:

RankGuru · Accepted Answer

1. **Formula**: Degree of dissociation ($\alpha$) for a weak acid is given by $\alpha = \sqrt{\frac{K_a}{C}}$ (valid if $\alpha < 5\%$ usually, but let's check).
2. **Values**: $K_a = 1.0 	imes 10^{-5}$, $C = 1.0 	imes 10^{-3} M$.
3. **Calculation**:
   - $\alpha = \sqrt{\frac{10^{-5}}{10^{-3}}} = \sqrt{10^{-2}} = 0.1$.
4. **Percent Dissociation**: $\alpha 	imes 100 = 0.1 	imes 100 = 10\%$.
5. **Note**: Since $\alpha$ is quite high ($10\%$), a more precise quadratic calculation might give a slightly lower value, but among the given options, **$10\%$** is the standard approximation expected using Ostwald's Dilution Law.

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Acid–base Equilibria

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