Question

Indicators change colors at specific pH ranges. Look up the pH for phenolphthalein. Indicators are used knowingly (and sometimes unintentionally) in everyday life.

a) What is the most common indicator used to measure pH of swimming pools? What color changes does it undergo?

b) Red cabbage juice is a common indicator you can make at home. What compounds are responsible for the indicator properties of red cabbage? What are the pH ranges in which it works?

Answer 1

Solution:-

a) --> The most common pH test for pool is the phenol-red test.

   --> The pH test that uses phenol red as a reagent is particularly effective (pH range of 6.8-8.2).

   -->Phenol red is available in either liquid or tablet form. To test with phenol red, add one tablet or a specified number of drops of liquid, to the water sample, and compare the resulting color to the test-kit standard. At the low end, the sample is yellow, developing an increasingly red color as the pH increases. At the high end, the color is almost purple.

b)   --> Red cabbage juice contains a natural pH indicator that changes colors according to the acidity of the solution. Red cabbage juice indicator is easy to make, exhibits a wide range of colors, and can be used to make your own pH paper strips.

--->Red cabbage contains an anthocyanin-based dye that can be used as a pH indicator. It is red, pink, or magenta in acids, (pH < 7), purple in neutral solutions (pH ~ 7), and ranges from blue to green to yellow in alkaline solutions (pH > 7).