Buffer ratio and Henderson–Hasselbalch relation
Rearranging the acid dissociation relation gives pH=pKa+log₁₀(aA⁻/aHA).
Key knowledge
Rearranging the acid dissociation relation gives pH=pKa+log₁₀(aA⁻/aHA). Replacing the activity ratio by a concentration ratio is an approximation. The relation describes equilibrium composition; finite buffer capacity additionally depends on the total amounts and competing equilibria.
Values and equations
pH = pKa + log₁₀[a(A⁻)/a(HA)]
- pH
- negative logarithm of hydrogen-ion activity 1
- pKa
- negative logarithm of acid constant 1
- a(A⁻)
- conjugate-base activity 1
- a(HA)
- acid activity 1
Conditions and scope
- Use a consistent solvent and pKa convention, with appreciable conjugate-pair amounts.
- It is not a formula for arbitrary pre-neutralization amounts; very dilute, strongly nonideal or nearly exhausted buffers require the full balances.
Sources · 1
References
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Evidence and review
Inspected the Henderson–Hasselbalch rearrangement and buffer-composition examples.
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Entry details
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- uni-chem-henderson-hasselbalch
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- core.1
- Structured reference record
- University core expansion