Classroom Activities and Printable Activity Sheets
The pH scale is logarithmic. A one-step change on the scale represents a ten-fold change in concentration of hydrogen ions (the amount of acid). Help your students understand the concentration of acids through this simple demonstration.
You will need: White vinegar, distilled water, pH test strips, a very large bowl, teaspoon measure, measuring cup
Directions: Follow the steps below in order. At the end of each step, note your results on a chart. Record the volume of vinegar, the volume of water, the total volume, and the pH and taste of the mixture.
Step 1: Measure 2 teaspoons of vinegar and place it in the bowl. Using a pH test strip, measure the pH of the vinegar. Taste a drop of vinegar from the original container. Record your results.
Step 2: Add 2 cups of distilled water to the vinegar in the bowl. Gently mix them together. Measure the pH of the mixture. Taste a drop of it. (Don't forget to record your results.)
Step 3: Add 8 more cups of distilled water and gently mix. Measure the pH and taste a drop of the mixture.
Step 4: Add 8 more cups of distilled water and gently mix. Measure the pH and taste a drop of the mixture.
Questions to think about:
What happens to the pH as more water is added?
What is the total amount of liquid in the bowl?
What fraction of the mixture is vinegar?
What fraction is water?
What has happened to the vinegar? (The vinegar has been diluted and is spread throughout the water.)
What does this tell you about the pH of normal lakes versus acidic lakes? (i.e., An acidic lake, with a pH of 5, is 100 times more acidic than a "neutral" lake with a pH of 7.) Normal rain versus acid rain? Acid fog?
(adapted from The Backyard Acid Rain Kit Program Guide from Public Focus)