When a buffer is infused with a strong acid, what is the effect on pH according to Henderson–Hasselbalch?

When a buffer is infused with a strong acid, what is the effect on pH according to Henderson–Hasselbalch?

• A. pH increases
• B. pH decreases
• C. pH remains unchanged
• D. pH becomes unpredictable

Answer: (B)

Buffer systems resist pH changes by shifting the equilibrium between the weak acid and its conjugate base. According to Henderson–Hasselbalch, pH = pKa + log([A-]/[HA]). When a strong acid is added, there are extra H+ ions that protonate the conjugate base A- to form more of the weak acid HA. This lowers the amount of A- and increases HA, causing the ratio [A-]/[HA] to decrease. A smaller ratio makes the log term more negative, so the pH drops. The buffer slows the change rather than preventing it completely, until its capacity is exceeded. So the pH decreases.

Buffer systems resist pH changes by shifting the equilibrium between the weak acid and its conjugate base. According to Henderson–Hasselbalch, pH = pKa + log([A-]/[HA]). When a strong acid is added, there are extra H+ ions that protonate the conjugate base A- to form more of the weak acid HA. This lowers the amount of A- and increases HA, causing the ratio [A-]/[HA] to decrease. A smaller ratio makes the log term more negative, so the pH drops. The buffer slows the change rather than preventing it completely, until its capacity is exceeded. So the pH decreases.