2 Preview information;Red cabbage contains a pigment molecule called flavin (an anthocyanin).This water-soluble pigment is also found in apple skin, plums, poppies, cornflowers, and grapes. Very acidic solutions will turn anthocyanin a red color.Neutral solutions result in a purplish color.
3 Basic solutions appear in greenish-yellow Basic solutions appear in greenish-yellow. Therefore, it is possible to determine the pH of a solution based on the color it turns the anthocyanin pigments in red cabbage juice.The color of the juice changes in response to changes in its hydrogen ion concentration. pH is the -log[H+].Acids will donate hydrogen ions in an aqueous solution and have a low pH (pH < 7).Bases accept hydrogen ions and have a high pH (pH > 7).
4 Materials: These are the materials that we are using during the experiment. red cabbageblender or knifeboiling waterfilter paperOne large glass beakerSix 250 mL beakershousehold ammonia (NH3)baking soda (sodium bicarbonate, NaHCO3)washing soda (sodium carbonate, Na2CO3)lemon juice (citric acid, C6H8O7)vinegar (acetic acid, CH3COOH)seltzer water (carbonic acid, H2CO3)muriatic acid or masonry's cleaner (hydrochloric acid, HCl)lye (potassium hydroxide, KOH or sodium hydroxide, NaOH)
5 Procedure; Chop the cabbage into small pieces . Place the cabbage in a large beaker and add boiling water to cover the cabbage. Allow at least ten minutes for the color to leach out of the cabbage.Filter out the plant material to obtain a red-purple-bluish colored liquid. This liquid is at about pH 7.
6 Pour about 50 - 100 mL of your red cabbage indicator into each 250 mL beaker. Add various solutions to your indicator until a color change is obtained.Use separate containers for each household solution .Be amazed as the beautiful colors dazzle and delight your eyes.
7 Results:Your red cabbage juice is a simple pH tester. It reacts differently to different substances.Once you know what colour the juice turns in acids and alkalis, you can use it to test other liquids.
9 Why It Happens:Red cabbage has pigments which react differently to acids and alkalis.When you dip the strips into a substance and wait for a few minutes, the colour will fully develop.The indicator strips turn red-yellow in acid, green in neutral and purple-blue in alkali.