A laboratory manual lists the following information for the indicator bromothymol green
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A laboratory manual lists the following information for the indicator bromothymol green.
• pKa=7.0
• Protonated form: yellow
• Deprotonated form: blue
A student prepares three separate buffered solutions with measured pH values of 6.0, 7.0, and 8.5, respectively, and adds a few drops of bromothymol green to each.
Answer the following questions about the appearance of the indicator in these solutions.
(1) For each of the three pH values, identify which structural form of the indicator (protonated or deprotonated) is present in the higher molar concentration. Justify your answer for each solution by referring to the relationship between pH and pKa.
(2) State the macroscopic color that the student will observe in each of the three solutions and explain how the microscopic composition leads to that color.