CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
Thymol blue (first transition) has a pKa of 6.3. Its protonated form appears red, whereas its deprotonated form appears blue. A biochemical assay is performed at pH 7.0, and thymol blue is added as a visual indicator.
Use the information above to analyze the behavior of thymol blue at pH 7.0.
(1) Calculate the ratio [protonated form][deprotonated form] for thymol blue in the assay solution.
(2) Using the ratio from part (a), determine the approximate percentage of thymol blue molecules that are in the blue form. Express your answer to the nearest whole percent.
(3) Based on your result in part (b), predict the overall color the analyst will observe when looking at the assay mixture and explain your reasoning.