The statement that best describes a buffer is: A buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added.
Why?
A buffer is a solution made by combining either:
- A weak acid (HA) and its conjugate base (A⁻).
- A weak base (B) and its conjugate acid (HB⁺)
The purpose of a buffer is to resist changes in pH when a strong acid or base is added to the solution.
If the buffer is composed of HA and A⁻ and a strong acid (e.g. HCl) is added, the buffer accepts hydrogen ions in the following way:
A⁻+HCl → HA+Cl⁻
If a strong base (e.g. NaOH) is added, the buffer donates hydrogen ions in the following way:
HA + NaOH → NaA + H₂O
The pH of the buffer at any given moment can be found by using the Henderson-Hasselbach equation, based on the equilibrium HA + H₂O ⇄ H₃O⁺ + A⁻
![pH=pKa+log([A^(-)] )/([HA])](https://img.qammunity.org/2020/formulas/chemistry/college/dekaz2g15ismnmzsk9vdry3s6d4dwxyo4w.png)
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