Explore Air

Acid Rain Lesson Plan

Activity 1 – the pH Scale

Time: 1 Hour

Behavioral Objectives

At the end of this lesson the student will be able to:

  1. Describe the pH scale and its components
  2. Explain why a pH measurement must be accurate and why small changes in pH are important.

Materials

You will need enough of the following for each student:

  1. Dried apricots
  2. Grapefruit pieces
  3. Lemon pieces
  4. Molasses
  5. Writing paper, pencils
  6. Four paper cups for each child

Instructions to Teacher

  1. Write on blackboard:
    • Molasses - pH 5
    • Dried Apricots - pH 4
    • Grapefruit - pH 3
    • Lemon- pH 2

    (Other common substances' pH can be found in Table 1)

  2. 2. After the students complete the following experiment, go back over the discussion on pH strengths (Sources of Acid Pollution 1 - 3).
  3. 3. Explain that the molasses the students tried had a pH of 5. The dried apricots had a pH of 4 and are 10 times more acidic than the molasses. Grapefruit (pH3) is 10 times more acidic than the apricots and 100 times (10 x 10) more acidic than the molasses. The lemons are 1,000 times (10 x 10 x 10) more acidic than the molasses.

Instructions to Students

  1. Sample each item. You may try any one of the four samples first.
  2. Record which sample tasted the least bitter, the most bitter. Rank them in that order. Save these answers for the discussion later.

Questions to Students

  1. How did you rank the four samples, least bitter to most bitter?
  2. Why did you rank them this way?
  3. Where do you think the following fruits and vegetables would be placed on the pH scale: Apples? Carrots? Spinach? Jams? (pH 3, 5, 5, 4, respectively)

updated on 04/20/2006  I   http://nature.nps.gov/air/edu/Lessons/Activity1.cfm   I  Email: Webmaster