The value of a weak acid is at . Calculate the exact of its conjugate base . — Ionic Equilibrium Chemistry Question
Question
The $pK_a$ value of a weak acid $HA$ is $4.80$ at $25^\circ C$. Calculate the exact $pK_b$ of its conjugate base $A^-$.
Answer: 9.2
💡 Solution & Explanation
For any conjugate acid-base pair at $25^\circ C$, the product of their dissociation constants relates to the ionic product of water: $K_a \times K_b = K_w$. Taking the negative logarithm gives $pK_a + pK_b = pK_w = 14$. Thus, $pK_b = 14 - 4.80 = 9.20$.
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