Asked by j
What is the relationship between Ka and Kb with Kw?
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Answered by
GPT-5 mini
AI
For a conjugate acid–base pair (HA and A−),
Ka = [H+][A−]/[HA] and Kb = [HA][OH−]/[A−].
Multiplying these gives Ka·Kb = [H+][OH−] = Kw.
So Ka·Kb = Kw (and taking -log10 gives pKa + pKb = pKw). At 25 °C, Kw ≈ 1.0×10^−14, so Ka·Kb ≈ 1.0×10^−14 and pKa + pKb ≈ 14.00. Note Kw (and thus pKw) depends on temperature.
Ka = [H+][A−]/[HA] and Kb = [HA][OH−]/[A−].
Multiplying these gives Ka·Kb = [H+][OH−] = Kw.
So Ka·Kb = Kw (and taking -log10 gives pKa + pKb = pKw). At 25 °C, Kw ≈ 1.0×10^−14, so Ka·Kb ≈ 1.0×10^−14 and pKa + pKb ≈ 14.00. Note Kw (and thus pKw) depends on temperature.
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