Pigments from the red cabbage help determine the pH of a solution. The pH scale is used to measure how acidic or basic a solution is. The scale used ranges from 0-14; a pH of 7 is neutral, less than 7 would be acidic and greater than 7 would be basic [1]. A pH indicator is used as a chemical detector for hydroxide and hydrogen molecules [2]. In the experiment, the red cabbage pigment called Anthocyanin was used as a pH indicator.
Anthocyanin is a water-soluble pigment that is classified as flavonoids. They provide color to most flowers, fruits and vegetables, including berries, apples, red cabbage, onions, eggplant etc. [3]. The objective of this experiment was to analyze the effects of pH on anthocyanin by using different chemicals. It
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Acids release hydrogen ions, while bases release hydroxide ions when put into a solution. When equal amounts of hydrogen and hydroxide ions are added, it produces water. If they aren’t enough H+ ions to combine with the OH-, the water will have extra OH-, making it mostly basic. Same occurs when there are less OH-, the water will be acidic. Anthocyanin is a molecule that adds and takes away hydroxide ions [4]. When KOH was added, the pH was 8, making the solution basic. The yellow color that also resulted from the KOH had a pH of 12, which is also basic. The HCl drops added had a pH of 4, which is acidic. When KOH is added to the pigment, OH- are attached to the structure of anthocyanin. However, when HCl drops are added, because of the acidity, OH- ions are removed in the structure. The results of this this experiment, supported the hypothesis. As showed in picture 1, anthocyanin in a base has 3 total double bonds in the center with a positively charged molecule. In the base structure of anthocyanin, there is a carbonyl group instead of 3 hydroxyl groups. Both structures are bonded to a sugar. An addition of an acid or base solution changes its structure and color of the