試題詳解

19. Two drops of indicator HIn (K_a = 1.0 × 10^-9 ), where HIn is yellow and In- is blue, are placed in 100.0 mL of 0.10 M HCl. The solution is titrated with 0.10 M NaOH. At what pH will the color change (yellow to greenish yellow) occur?
(A) 7.0
(B)8.5
(C) 9.0
(D) 7.5
(E)8.0