Andrea is performing an experiment in which she needs to know when a strong acid is present. She is not sure which indicator to use, so she looks up the following table in her science textbook. According to the textbook, which indicator should Andrea use?
Hint: Neutral substances have a pH of 7. Acids have a pH that is less than 7, and bases have a pH that is greater than 7.
thymol Blue
phenol Red
phenolphthalein
trinitrobenzoic acid