Bromothymol blue is a common acid-base indicator. It has a K_a equal to 1.6 * 10^-7. Its un-ionized form is yellow and its conjugate base is blue. At a pH of 5.8 the color in the solution would be yellow.

Question

Quizplus · Accepted Answer

At pH 5.8, which is below the pKa (pKa = -log(Ka) = 7 - log(1.6) ≈ 6.8), the solution is more acidic, favoring the un-ionized yellow form of bromothymol blue.

Bromothymol Blue Is a Common Acid-Base Indicator