The indicator propyl red has K_a = 3.3 $\times$ 10^-6.What would be the approximate pH range over which it would change color? A)3.5-5.5 B)4.5-6.5 C)5.5-7.5 D)6.5-8.5 E)None of these choices is correct.

Question

Quizplus · Accepted Answer

Propyl red has a transition range of pH 6.8-8.0 according to its pKa. However, based on the given indicator equation, the pH range would be shifted to a lower range of approximately 4.5-6.5, where the color change occurs. Therefore, the best choice is B, 4.5-6.5.

The Indicator Propyl Red Has Ka = 3 ×\times× 10-6

The Indicator Propyl Red Has K_a = 3 $\times$ 10^-6