Explain how buffer capacity depends on concentrations and pH range.

Explain how buffer capacity depends on concentrations and pH range.

• A. Buffer capacity scales with the total concentrations of the weak acid and conjugate base; effective pH range is around pKa ± 1.
• B. Buffer capacity is independent of concentration.
• C. Buffer capacity depends only on temperature.
• D. Buffer capacity decreases as total concentration increases.

Answer: (A)

Buffer capacity is about how much strong acid or base a solution can neutralize before the pH shifts significantly. It depends on how much buffering material you have—the total amounts of the weak acid and its conjugate base. When you increase both components while keeping their ratio the same, you’ve simply got more moles available to react with added H+ or OH−, so the buffer can absorb a larger amount of added acid or base and the pH changes more slowly. The pH range over which a buffer is effective is set by the ratio of base to acid, described by pH = pKa + log([A−]/[HA]). The buffer works best when this ratio is near 1, meaning the pH is close to the pKa, and you can adjust the ratio to counteract added acid or base with only modest pH changes. A common practical guideline is to consider the buffer effective within about pKa ± 1. Outside that window, one form dominates and the capacity to resist pH changes drops. So the correct idea is that capacity scales with how much buffer material is present, and the useful pH range sits around pKa ± 1.

Buffer capacity is about how much strong acid or base a solution can neutralize before the pH shifts significantly. It depends on how much buffering material you have—the total amounts of the weak acid and its conjugate base. When you increase both components while keeping their ratio the same, you’ve simply got more moles available to react with added H+ or OH−, so the buffer can absorb a larger amount of added acid or base and the pH changes more slowly. The pH range over which a buffer is effective is set by the ratio of base to acid, described by pH = pKa + log([A−]/[HA]). The buffer works best when this ratio is near 1, meaning the pH is close to the pKa, and you can adjust the ratio to counteract added acid or base with only modest pH changes. A common practical guideline is to consider the buffer effective within about pKa ± 1. Outside that window, one form dominates and the capacity to resist pH changes drops. So the correct idea is that capacity scales with how much buffer material is present, and the useful pH range sits around pKa ± 1.