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8.9 Henderson-Hasselbalch Equation

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Henderson Hasselbalch Equation

An important equation to remember for buffers is the Henderson-Hasselbalch Equation, which relates pH, ${K_a}$ , and the concentration of the buffer components.

pH = pK_a + log([A^–]/[HA])

Where

{[A^-]}

is the concentration of the conjugate base and

{[HA]}

is the concentration of the acid. Note that, this can be easily derived by expanding the logarithms.

Importantly, strong acids and strong bases cannot be used to make buffers, as they will always fully dissociate into their ions. For example, {Cl^–} will not bond with any added

{H^+}

to form

{HCl}

, as

{HCl}

is a strong acid. {Cl^–} is therefore considered a negligible base.

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