by Alaa Yahya
An indicator is a substance that changes color when added to another product, due to presence of an acid or base. The indicator we used in this experiment was a red cabbage juice.
Why is red cabbage a good indicator?
Red cabbage is a good indicator because it contains a pigment or coloring agent called Anthocyanin. Acid and bases are compounds that release hydrogen ions, however, Anthocyanin are complex molecules that can add and subtract hydroxide ions. Now, if you put anthocyanin in acidic solution, OH- will pop of the anthocyanin molecules. In basic solution, OH- in the water will hop into the anthocyanin molecules. Moreover, what makes anthocyanin an indicator, is that each form of the compound reacts with light differently, so that each form is a different color. All acid-base indicators, in fact, change color because they change their structure in some way( Posted by: Sue Klemmer, Secondary School Teacher science)
An acid has a pH less than 7. So, to identify an acid, we should add our indicator and the color must change to red, pink or purple.
Proof of my experiment
Make your OWN pH Indicator from Red Cabbage!