Acid-Base Testing
Gateway to Science presents
“Chemical Reactions”
Some substances are classified as either an acid or a base. Acids and bases are opposites. Scientists can tell
if a substance is an acid or a base by using an indicator. An indicator is typically a chemical that changes
color if it comes in contact with an acid or a base. This experiment will teach you how to make your own
indicator using cabbage juice.
Properties of Acids and Bases
Acids: Compounds that produce hydrogen ions in water. Most common acids contain oxygen.
Bases: Compounds that produce hydroxide ions in water. Bases that are soluble in water are called alkali.
Characteristics of Acids:
1. Sour taste and many have a strong smell.
2. Strong acids burn and sting, can even dissolve metals.
3. An acid has a pH less than 7 and turns blue litmus paper red.
4. Acids are neutralized by bases – Antacid tablets (base) neutralize the acid in the stomach and baking
soda (base) neutralizes the acid in insect bites.
5. Acids react with carbonates to produce carbon dioxide.
a) Acid rain reacts with limestone rock (calcium carbonate) used in buildings and statues like those
at the state capital.
b) Stomach acid reacts with Tums (calcium carbonate).
c) A baking powder mixture, cream of tartar (acid) reacts with baking soda (sodium bicarbonate).
Characteristics of Bases:
1. Bitter taste and a slippery feel.
2. Strong alkalis burn your skin and have the power to dissolve.
3. Bases are neutralized by acids to produce salts.
4. Bases have a pH greater than 7 and turn red litmus paper blue.
5. Some plants like alkaline soil. Hydrangeas will only produce pink or white flowers in alkaline soil. In
acidic soil they produce blue flowers.
6. Chocolate cakes become quite bitter if too alkaline.
Materials:
Red cabbage – Ziploc Bags – Warm Water – Clear 1 oz. Cups – Toothpicks – White Paper
Test chemicals: Vinegar & Ammonia needed (Other suggestions: Lemon juice, 7-Up, Windex, Liquid Soap,
Antacid Tablets, Baking Soda)
Experiment:
First, make an indicator out of red cabbage. Here how...
1. Tear a cabbage leaf into very small pieces and put them in a ziploc bag with about 1/4 cup of very
warm water. Close the bag tightly and with as little air as possible.
2. Use your fingers to rub and squish the cabbage inside the bag until the liquid is very purple.
Now, let’s test some common household products to find out if they are acidic or base.
1. Set out 3 small cups, side by side on a white piece of paper. Fill each cup half full with cabbage juice.
2. Since you know that vinegar is an example of an acid, add a few drops of vinegar to the first cup of
cabbage juice. Stir with a spoon and notice the color change, indicating that vinegar is classified as
an acid.
3. In the second cup, add a few drops of ammonia. Notice the color change, indicating that ammonia is
a base.
4. Try adding a few drops of another chemical to the third cup and note the color change to determine
if it is an acid or a base.
Try This:
Add a few drops of a base to your acid solution (vinegar). Also try adding an acid to your base solution. Can
you get the color to change back to the original purple of the indicator? This is called “neutralizing.”
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