Question:

At 27°C, the degree of dissociation of HA (weak acid) in 0.5 M of its solution is 1%. The concentrations of H\(_3\)O\(^+\), A\(^-\), and HA at equilibrium (in mol L\(^{-1}\)) are respectively:

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The degree of dissociation (\( \alpha \)) for weak acids helps determine ion concentrations at equilibrium.
Updated On: Mar 13, 2025
  • \( 0.005, 0.005, 0.495 \)
  • \( 0.05, 0.05, 0.45 \)
  • \( 0.01, 0.01, 0.49 \)
  • \( 0.005, 0.495, 0.005 \)
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The Correct Option is A

Solution and Explanation

Step 1: Define Dissociation Equation For a weak acid HA dissociating in water: \[ HA \rightleftharpoons H_3O^+ + A^- \] 
Step 2: Compute Concentrations Given initial concentration: \[ [HA] = 0.5 \text{ M}, \quad \alpha = 1\% = 0.01 \] \[ \text{Dissociated amount} = 0.5 \times 0.01 = 0.005 \text{ M} \] \[ [H_3O^+] = [A^-] = 0.005 \text{ M}, \quad [HA] = 0.5 - 0.005 = 0.495 \text{ M} \]

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