Cabbage Indicator
Red cabbage has a type of pigment, an anthocyanin, called flavin. Flavin is also responsible for the coloring of apples, plums, poppies, and grapes. When anthocyanin is placed in solutions of different pH levels, it turns color. This demonstration uses red cabbage juice to indicate the pH level of different solutions. Add water to chopped red cabbage and mix in a blender to obtain the juice.
Vinegar is a strong acid. Acidic solutions turn the anthocyanin a red color. The color of the red cabbage juice changes when its hydrogen ion concentration is altered. In an acidic solution, the acid donates hydrogen ions to the cabbage. The solution turned red, indicating the pH of the vinegar to be 2.
Ammonia is a strong base. Basic solutions turn the anthocyanin a greenish-yellow color. In a basic solution, the base accepts hydrogen ions from the cabbage. The solution turned, greenish-yellow, indicating the pH of the ammonia to be 12.
Students can experiment with various products to test their pH. In this demonstration, the red solution is the acidic vinegar. The greenish-yellow solution next to it is the basic ammonia. In the upper right corner is a solution of water and baking soda. The bluish-green color indicates that baking soda is basic, pH 10. The solution in the lower left corner is sugar. The violet color implies that sugar is slightly acidic with a pH of 6. The lower middle solution is salt water. The darker purple color shows that salt is more acidic than sugar, pH 4. Finally, the lower right solution is an antacid tablet dissolved in water. Its bluish color indicates that the tablet is slightly basic, with a pH of 8. When someone has heartburn (stomach acid coming up the esophagus), the antacid tablet they take neutralizes the acid by counteracting its low pH!
