Observations and results
Did the indicator solution change color when you added the lime or lemon juice, vinegar and bleach? Did the solution color indicate that the lime or lemon juice and vinegar were acidic (had a lower pH) and that the bleach was basic (with a higher pH)?

A solution with a pH between 5 and 7 is neutral, 8 or higher is a base, and 4 or lower is an acid. Lime juice, lemon juice and vinegar are acids, so they should have turned the indicator solution red or purple color. Bleach is a strong base, therefore it should have turned the indicator solution a greenish-yellow color.

How basic or acidic a solution is depends on the amount of hydrogen ions in it. A basic solution accepts hydrogen ions (or donates electron pairs as hydroxide ions) whereas an acidic solution donates hydrogen ions (or accepts electron pairs). An indicator, like anthocyanin, responds to the levels of hydrogen ions in the solution. Anthocyanin and other biological pigments absorb certain wavelengths of light and reflect others, and it is the reflected light we see that makes them appear a certain color. Depending on the levels of hydrogen ions in the solution, the indicator pigment undergoes a chemical reaction that changes its chemical structure, making it reflect a different wavelength of light and thereby change color.

Cleanup
Dilute the bleach solution with water before pouring it down a drain. (Remember to keep your goggles on when you do this.)

More to explore
"Experiments with Acids and Bases" from Fun Science Gallery
"Acids and Bases Are Everywhere" from Rader's Chem4Kids.com
"Acids, Bases, and the pH Scale" from Science Buddies
"Cabbage Chemistry" from Science Buddies


This activity brought to you in partnership with Science Buddies

1 Comments

1. 1. fountaindiver 12:57 PM 3/6/12

   This is a very good article. I might try this with my son when he gets a little older. I had heard that red cabbage was a good ph indicator. http://critcherbrothers.com

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