by Naomi White, Science Teacher, Jefferson High School, LAUSD

LESSSON SHEET

[ Student Handout | Data Sheet ]

Time frame: one period

Concept:
Hardness is the amount of magnesium and calcium in water. Hard water makes washing more difficult and causes mineral deposits which corrode pipes. In aquatic ecosystems, it affects the pH and in turn the biodiversity.

Objective:
Students will use a hardness test kit to measure the hardness of both tap water samples and samples from natural bodies of water.

Materials:

• LaMotte Hardness Test kit (price: $22.50/call: Frey 1-888-222-1332/kit#: F22210)
• Copper and iron test kit (price: 54.50/call: Frey 1-888-222-1332/kit#: F02088)
• hot plate
• pan
• water sample from natural body of water
• tap water samples
• distilled water
• liquid hand soap

Preparation:

1. Collect water samples

Procedure:

1. Add a small amount of water in a pan and begin heating it.
2. Ask students to predict what will happen.
3. Discuss water hardness. Add a drop of soap to a test tube of distilled water and a test tube of tap water.
4. By now the water should have boiled away. Show students the white residue. Let them make observations on their chart.
5. Ask students what things are important for tap water (such as sterility, taste, odor, etc.). Explain that DWP and MWD water comes from various sources including the Colorado River (why our water is so hard), and that the water may differ in different parts of the city.
6. Send students to make samples of water from various locations around the school. Explain how to use the two kits. Let students conduct the test and record the result on the board. Each group can conduct one test on one sample (one group should test the natural body of water sample). Students will copy the compiled data from the board. Assign a student to enter data on computer.
7. When results from other schools have come back, discuss possible causes for differences. Have students mark each school on the map, and record the data from around the city.