Cabbage Juice Indicator

Chemists use indicators to test whether a substance is an acid or a base. Indicators work by turning a distinctive color in the presence of an acid or a base. You can make your own indicator from red cabbage. You can also make indicators from the juice of elderberries, blackberries, radish skins, apple skins, or cherries.

Materials

Substitutions

hot plate

 

1 head red cabbage

 

food processer

knife and cutting board

1000 mL beaker

large size saucepan

500 mL beaker

large jar

4-5 250 mL beakers

4-5 small jars

sieve

tea strainer or collander

substances to test **

 

distilled water

 

rubbing alcohol

 

** recommend materials: baking soda, bathroom cleaner (e.g. Formula 409™), washing soda, vinegar, lemon juice, milk, cream of tartar, orange juice, milk of magnesia, lime, soft drinks, or ammonia

Procedure

1.      *Chop red cabbage up finely. Boil a pint of water in a saucepan.

2.      *Add the red cabbage carefully to the boiling water and take the saucepan off the heat. Let it stand for 30 minutes or until it is completely cool.

3.      *Strain the liquid into a jar and throw away the used cabbage. The liquid should be a dark reddish-purple color. Add rubbing alcohol, or refrigerate, to reduce the spoilage of the indicator. Use a 1 : 5 ratio of alcohol to water.

4.      The color will change as you add acids or alkalis. To test a substance, pour a small amount of your substance into a small jar. Then add a drop or two of the cabbage juice indicator. A change in color indicates its acidity or basicity.

 

 

Colors of Red Cabbage Juice and Different pH values

color          red              rose     purple     blue               green       yellow

pH              1   2    3   4    5    6    7    8   9  10   11   12   13   14

        ACID                                neutral                                      BASE

 

 


Data and Observations

Substance

Color

Approximate pH

Acid or Base?

lemon juice

 

 

 

lime

 

 

 

washing soda

 

 

 

ammonia

 

 

 

cream of tartar

 

 

 

muriatic acid

 

 

 

Formula 409™

 

 

 

baking soda

 

 

 

vinegar

 

 

 

Sprite™

 

 

 

Extensions

Soak some filter paper in the cabbage juice indicator. Allow the paper to dry, then cut it into strips. Conduct an "at home" pH test of other household items. Tape your strips to a piece of notebook paper and bring them back to class. Compile your results. What can you say about household cleaners? Where are most household acids found?