Materials and Resources

pH Lesson Plan

Key Understandings:

• What pH is and some common values
• Why it is such an important factor in Water Quality
• Some main factors that affect pH in a lake / river
• What influence pH can have on the lake/river environment
• How to measure it using litmus paper & color comparator kit.

Time needed:

We suggest taking 1 full lesson to discuss and do a practice lab on this topic. The lab should only take the students about 15 minutes to complete.

Discussion:

Discussion opening: What is pH? Groups work for 3 min to come up with their own definitions; discuss as a class.

• Review common values of pH
• Discuss importance of pH in water quality: reactions, solubility, aquatic life
• Discuss what affects pH levels in lakes & rivers and how (if time remains)
• Demonstrate the proper technique for measuring pH with indicator paper and with the color comparator provided by the Massachusetts Water Resources Authority (MWRA)

Lab:

• Test tap water in a beaker using indicator paper and the MWRA color comparator. Which test is more accurate?
• Blow air into this same water for a minute through a straw. You are adding CO2 to the water from your breath. Measure pH again with the two methods.

Homework:

• Read CBL pH handout (first two pages)
• Answer the following questions using your lab data (you may need to look on the MWRA web site for some of the answers):
  • Did the two methods produce the same results? If not, which one do you think is more accurate?
  • Why did the pH change after blowing into the beaker? Does this effect occur in nature?
  • Why was the pH of tap water so high?

Handouts:

Vernier Software: Water Quality with CBL - pH

As an alternative to the CBL pH handout, you may use the MWRA pH handout

Alternatives to this test, comments and further resources:

It is certainly helpful if pH and acids & bases were studied in the class prior to teaching this unit. Most students understood the concept and the pH range rather well; many had difficulty, however, with understanding the factors that affect pH in a natural water body. We therefore, recommend that you allocate sufficient time for this in your presentation / discussion.

We chose these two tests for pH because they are simple, visual, and give the students more of a sense of doing "wet" chemistry. The CBL pH system, however, is a good option as well. If you are unable to obtain color comparators of the type MWRA lends out, any liquid universal indicator with a good color comparison scale would do.

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