Humboldt State University ® Department of Chemistry

Richard A. Paselk

Science 331
Fall 2004 Lecture/Activity Office: SA560a
Notes: 15 September Phone: x 5719
Home: 822-1116
e-mail: rap1

Acids and Bases

What are acids and bases? There are three major definitions. We will look at two (the third is not needed for our study).

We will use the practical definition in our activity today. We are going to explore the acid/base nature of a variety of substances using a natural indicator, the dye in "red" cabbage, and litmus paper, and acid/ base indicator paper. First we will have to prepare the indicator dye from the cabbage. We will then use this dye to explore the acidity/basicity of a variety of substances common in daily life.

Cabbage Extract: Boil some distilled water (about 300mL) in a large beaker (600mL). Turn off the heat and add cabbage (about 300mL) which has been torn into small pieces. Allow the cabbage to sit with occassional stirring until the water is colored deep blue.

For your work today we will take small samples (a few drops) of a variety of substances in water. You can then test them with litmus followed by adding a drop or two of your cabbage indicator. Write your observations in the table (Note - acids taste sour! Use this information and your own background to decide what the different colors mean etc.):

   Observations Conclusions
Test Substance Red litmus Blue Litmus Cabbage Indicator Acid Base Neutral
Lemon Juice            
Bleach (dilute)            
Ammonia (dilute)            

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© R A Paselk

Last modified 17 September 2004