PH is an indicator of how acidic or basic a substance is. The pH scale ranges from 0 - 14, with 7 representing neutral. Acids have a pH below 7; bases, a pH greater than 7. Scientists determine the pH of a substance by using an indicator; indicators change color depending on the pH of a substance. Different indicators work at different pH ranges, as seen in the table above. The transition range of an indicator is the range of pH when the indicator changes from its low-pH color to its high-pH color. If the indicator shows a color between the two, then the pH lies somewhere in that transition range.
Student groups are given an unknown liquid to test using the four indicators. One group conducts the tests and records these results.
Color Changes - pH Indicators
Indicator Used Color Produced
Methyl violet Bluish
Bromophenol blue Yellow
Phenolphthalein Colorless
Thymolphthalein Colorless
Using the table of indicator values, determine the approximate pH of the unknown solution.
A) 1.6
B) >3.0
C) between 0 and 1.6
D) between 1.6 and 3.0