Practice Test 2

Two buffers are prepared using the same conjugate pair with $pK_a = 6.5$. Buffer A is adjusted to pH 6.5 with total buffer concentration 0.020 M. Buffer B is adjusted to pH 6.5 with total buffer concentration 0.200 M. Both are challenged with the same small amount of NaOH. Buffer capacity increases with total concentration when the ratio is held constant. Which result is most consistent?

(Assume negligible dilution by the added NaOH.)

A buffer is prepared using $\mathrm{HA/A^-}$ with $pK_a = 8.0$. The solution is adjusted to pH 8.0 with $\mathrm{HA} = \mathrm{A^-}$. The researcher then adds a small amount of strong base. Which statement best describes why the pH change is limited?

Relevant reaction: $\mathrm{HA + OH^- \rightarrow A^- + H_2O}$. Buffer capacity depends on having sufficient HA to neutralize added base.