Material
Exact Color
pH
  Material
Exact Color
pH
             
             
             
             
             
             
 
 
 
 
 
Approx PH
2
4
6
8
10
Color of
extract
Red
Purple
Violet
Blue
Blue-Green
12
Green
Acids are substances that have specific properties that are the same. Bases or "alkalis" are materials with an entirely
different set of properties. We  will investigate these properties with things that are found around the house.  Additionally, we
will learn how to use the pH scale to describe acids and bases.


One of the most fascinating things about
acids and bases is their ability to change the color of specific vegetable materials.
Red cabbage is one of the most common vegetables whose color responds to acids and bases. For this experiment we
need to prepare some extract of red cabbage. With that we can investigate the color changes. To start, get 2 cups of red
cabbage and cut into 1-inch cubes. Put the cubes into a blender. Add 1 cup water and blend until the cabbage is nothing but
tiny scraps. Strain the mixture to get any chunks out. The remaining liquid (the red-cabbage extract) will be used for the
experiments.


Look at the ingredients on a bottle white vinegar. It most likely lists acetic acid. This illustrates vinegar is an acid.
Next examine what effect an acid has on the color of the red cabbage extract. Put ½ cup of vinegar into a clear glass. Add 1
teaspoon of red cabbage extract. Mix it up with a clean spoon and record the color in the box below.





Save the acid mixture in this glass to use as a reference.


Next let's test laundry ammonia on the color of red cabbage. Put ½ cup of laundry ammonia into a different clear  glass. Add
1 teaspoon of the red cabbage extract and mix. Write the color of this mixture in the box.




The laundry ammonia is a base or alkali.  The changing color of cabbage extract tells us whether the substance mixed in is
an acid or a base. We call cabbage extract an acid-base indicator. Save the base mixture in this glass to use as a reference.

Let's test the properties of baking soda (a solid). Spoon 1 teaspoon of baking soda in a glass and add ½ cup of water. Mix
until the baking soda has dissolved completely . Next, add 1 teaspoon of the red cabbage extract. Record the color of the
mixture in the box below.




The color of the baking soda mixture is different from the color of the acid (vinegar) mixture and also different from the
ammonia (base) mixture.

The cabbage extract illustrates whether a substance is an acid or a base. It can also be used to test how strong the acid or
a base is. We will use the pH scale to show how acidic (acid) or basic (base) our substances are. A pH reading under 7
shows that a substance is acidic. The lower the number, the more acid it has. A pH reading over 7 means that the material
is base. The bigger the number, the more base it has. Cabbage extract will show varying colors for different pH readings.
The colors and approximate pH values are on our chart at the bottom of this page.  


                                              What is the pH of vinegar?   

                   What is the pH of ammonia?  

   

  What is the pH of the baking soda ?  

Repeat the steps we used above to test the pH of other clear liquids, such as Sprite or 7-Up or lemon juice. Write down
what happens. Also test white liquids like milk or coconut juice and record the results. Test solids that are able to dissolve
in water like sugar and salt.  Other possible things to test include liquid soap and detergents,  shampoo, antacids, aspirin
or whatever you can think of. Be creative and have fun! Use the chart below to record your test results.
 
Materials Needed:

-
Red Cabbage
- Clear Cups
- Ammonia
- Baking Soda
- Blender
- Measuring Spoons
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