Is Red Cabbage Juice REALLY Red?

(OR How Can Acids and Bases Be Identified?)

 

I. Introduction : Acids and bases can be identified by using a substance that changes color when mixed with an acid or with a base. Those substances are called indicators. In this lab, you will use red cabbage juice as an indicator to test some substances to see if they are acids or bases.

II. Materials: Safety goggles, tape, marker, 6 small cups or a microplate and droppers, lemon juice, ammonia, baking soda solution, boric acid solution, tap water, red cabbage juice.
 
III. Procedures:
a. Put a strip of tape on each cup. Label the cups: vinegar, lemon juice, ammonia, baking soda, boric acid, and tap water. If you are using a microplate, place the plate on a piece of white paper and label the wells on the paper.
b. Put on safety goggles, Pour the liquids into the labeled cups or use droppers to add the liquids to the wells.
c. Observe the color of each liquid. In a table, record the color of each liquid. Smell each one carefully. Your teacher will show you how to do this. Record the smell of each liquid in your table.
d. Put about two spoonfuls of red cabbage juice in each cup or add a few drops to each well in the microplate. Red cabbage juice turns blue-green in a base and dark red or purple in an acid. Record any color changes in your table.

 



IV. Results :
Which of the liquids were acids?



Which were bases?



What is the red cabbage juice called?



Were any of the liquids neutral (neither acid nor base)? How could you tell?



V. Additional Activities : This activity can be expanded to use other indicators such as litmus paper, phenolphthalein, or others. Also, other household products can be tested such as furniture polish, cleaners, and fruit juice.

| RETURN to Elementary Chemistry Activities Page. |