Level Primary, Elementary

Concept

We use litmus, phenolphthalein and bromothymol blue as pH indicator. Instead of  them, we can make simple pH indicator by purple cabbage.

Materials

purple cabbage(one-quarter), kitchen knife, cooking pan, water, bottle, and electric heater or gas range

Procedure

(1)Cut purple cabbage into small pieces.

(2)Put cabbages and water in the cooking pan.

(3)Heat it until the cabbages become colorless.

(4)Keep the color water in the bottle.

(5)Let’s confirm the color change in the various water solutions.

Heat it and make red color water solution.

Science

Where does the color come from the purple cabbage?The purple color in purple and red cabbage comes from a class of pigment molecules called anthocyanins. It turns out that anthocyanins are found in flower petals, leaves (it makes them turn red in the fall.) and some fruits such as blueberries. Anthocyanins are plant pigments known as flavenoids and produce red, pink, violet and magenta colors in the various plant parts.One of the things that changes the color on anthocyanins is the level of acid or alkali (i.e., pH) around the molecule. Because the color of the anthocyanin is affected by the
pH of the environment, these molecules can tell you the pH of any substance.