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Chemistry · EQUILIBRIUM
हिन्दीA salt \( \text{CH}_3\text{COONH}_4 \) is dissolved in water at 298 K. Given \( pK_a(\text{CH}_3\text{COOH}) = 4.76 \) and \( pK_b(\text{NH}_4\text{OH}) = 4.74 \). If the solution is diluted 10-fold by adding pure water, the pH of the final solution will:
Correct answer · Option 4
remain unchanged at 7.01
Explanation
For a salt of weak acid and weak base, \( pH = 7 + \frac{1}{2}(pK_a - pK_b) = 7 + \frac{1}{2}(4.76 - 4.74) = 7.01 \). This formula is strictly independent of the concentration of the salt solution, so dilution does not alter the pH.
