Question

Cabbage juice is an example of a chemical indicator that changes colors over a broad range of pH values. Use the Internet to determine the nature of three other indicators: phenolphthalein, congo red, and bromthymol blue. In the space that follows, write the name of each of these three indicators, its natural color, the color(s) that it changes to, and the pH range that the color change(s) occur.

Answer 1

Phenolphthalein is naturally colorless. It is colorless at pH < 7 and turns pink and pH > 8.3

Congo Red is naturally red. At pH 3.0 it is blue-violet and it changes to red color at pH 5.0.

Bromothymol blue has a blue color at PH > 7 and changes to yellow at pH < 7).

Step-by-step explanation

Phenolphthalein is naturally colorless but turns pink in alkaline solutions. At acidic pH level, the indicator remains colorless throughout and when it comes to a pH level of 8.2 it begins to turn pink.

Congo Red is an indicator dye that is naturally blue-violet at pH 3.0 and red at pH 5.0

Bromothymol blue has a blue color when in basic conditions (pH over 7), a green color in neutral conditions (pH of 7), and a yellow color in acidic conditions (pH below 7)