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The pH Level of Pool Water: Back to School Science Lesson

written by: Kathy Foust • edited by: Donna Cosmato • updated: 8/10/2014

Students are often not all that anxious to return to school. Let them bring some of their summer with them as you complete this pH indicator experiment that gives them some useful information about their pools.

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    What are pH levels?

    The pH Level of Pool Water Science Lesson Before getting into a description about pH balance, begin a discussion with your students to see how many of them have pools or helped clean pools over the summer. This is a great way to give your students an opportunity to talk about their summer, which they are probably just itching to do! Some of the topics to touch on concerning pool water are listed below.

    • Did they help clean the pool?
    • What was the most common problem with the pool?
    • Did they find that some methods worked better than others?
    • Did they regularly check the pH levels of the pool?

    Follow this discussion up by offering the following description of pH levels.

    pH levels are also known as potential hydrogen levels because the measuring of the pH level is actually the measuring of the concentration of hydrogen atoms. The pH scale goes from 0-14 with 7 being the neutral zone. Anything below 7 is said to be acidic while anything measuring over 7 is said to be basic.

    When it comes to pools, the recommended levels usually range between 7.2-7.6 on the pH scale. Pools should be tested roughly about twice a week. So, what happens when the pH levels are not where they should be? The effects of a high or low pH level can actually be similar to each other, which is why it's important to take a measurement rather than just looking at the water. Pools with pH levels that are not right will cause eye and skin irritation, possible hair loss, corrosion of pool equipment and cloudy water. There are chemicals available that can change the pH level, as will be seen on this pH indicator experiment.

    When you have reviewed the above information to your students, continue on with the activity listed in the next section.

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    pH Indicator Experiment

    This is a really simple experiment that the students can have a bit of fun with. For the experiment you will need 8 clear plastic cups or petri dishes, 4 lids or some other way to cover the containers, 16 pH test strips, sea salt, bleach, 10 pennies and a gallon of tap water. Follow the instructions below to complete the experiment.

    1. Fill all 8 cups with water. Label each cup as you fill it in the steps below.
    2. Mix a teaspoon of sea salt in two of the cups.
    3. Place a capful of bleach in two of the cups.
    4. Split the 10 pennies between two of the cups.
    5. Measure and document the pH levels of all the cups.
    6. Cover 1/2 the cups so that there is one cup covered that has only tap water, one covered that has tap water and bleach, one cup covered that has tap water and pennies and one cup covered that has tap water and sea salt. Leave the other cups uncovered.
    7. Place all the cups on the windowsill where they have access to sunlight.
    8. At the end of the week, check the pH levels to see what has changed. Record the results.

    Explain that the things that were placed in the water are all commonly put in water to keep it clean. Everything that is put into water has an effect on the pH level, even sunlight. Discuss the changes in pH levels that are recorded in this pH level indicator experiment. Some topics to discuss are listed below.

    • What effect, if any did the sunlight have on the pH of the water?
    • Discuss how the water looks in each cup.
    • What is the pH level of the cloudiest water?
    • What is the pH level of the clearest water?
    • Are students surprised by the results of the experiment?