試題詳解

44. The phosphate buffer system is maximally effective at a pH close to its pKa of 6.86 and thus tends to resist pH changes in the range between about 5.9 and 7.9. What is the pH of a mixture of 0.05 M NaH₂PO₄ and 0.5 M Na₂HPO₄?
(A) 5.86
(B) 6.86
(C) 7
(D) 7.86