Hard Water Study*

Teacher Version(.doc)

Student Version(.doc)

• Grade Level(s):  8th
• Primary Focus: Science; NC Standard Course of Study Areas: 8th: 3.05, 4.04
  • (Key concepts:  Conductivity, solutions, and properties of water)
• Secondary Focus: Math; NC Standard Course of Study Areas: 7th: 4.01; 8th: 4.01
  • (Key concepts:  Height and complex units)
• Computer/Technology Skills: Calculators, Probeware, Data Visualization; NC Standard Course of Study Areas: 6th: 3.01, 3.03, 3.06; 7th: 1.10, 3.01, 3.02; 8th: 2.06, 3.01
• Essential Question:  Why does soap create more or less suds in different cities?How is water hardness detected?  What causes water hardness?
• Summary of Activity:  There are two parts of this experiment.  In Part I, students in small groups will test hard and soft water by measuring soap suds height and with the conductivity probe.  In Part II, these same groups will test unknown water types to determine the hardness of the water.
• Cognitive Teaching Strategies: Samples of hard water and soft water are difficult to differentiate based on looks alone.  In order to determine the properties of each solution, experiments need to be conducted.
• Materials:
  • Conductivity Probe(1 per group)
  • TI graphing calculator (1 per group)
  • EasyLink data interface (1 per group)
  • 25mL graduated cylinder
    (1 per group)
  • Ivory liquid soap
  • Eye dropper
  • 3 containers with tight lids (per group)
  • Different examples of water types: distilled water, very hard water & tap water.
  • 3 small beakers (per group)
  • Ruler (1 per group)
  

Part IA: Soap Sudsing Tests

1. Place 10 mL of distilled water in one container. Place 10 mL of very hard water in a second container. Place 10 mL of tap water in a third container.
2. Add one drop of Ivoryâ liquid soap to each container and cover tightly with lids. Shake each container the same number of times.
3. Use a ruler to measure the suds height (in cm) in each container. Record the results in the Data table.

Part IB: Conductivity Tests

1. Fill a clean beaker halfway with distilled water. Fill a second beaker halfway with very hard water, and the third beaker halfway with tap water. 
2. Connect the Conductivity Sensor and calculator with the EasyLink cable. Set the Conductivity Probe on the 0–2000 µS/cm position. 
3. Set up EasyData for data collection.
   1. Start the EasyData application, if it is not already running.
   2. Reset the application by selecting file->new.
   3. Select Events with Entry from the setup menu.
4. Measure the conductivity for each of the three water samples.
   1. Raise the beaker until the hole in the probe end is completely submerged in the solution. Swirl the solution briefly.
   2. Once the reading is steady, record the conductivity reading.
   3. Before testing the next sample, carefully blot the probe dry with a tissue.

Part IIA: Water Hardness Study

1. Use the skills you gained in Part I and do a study of water available in your community. You might compare surface water (from streams and ponds) with groundwater (from wells and springs). A study of the different bottled waters sold at local stores can also be done. Have students discuss why different water sources have different hardness levels.

Instructional Strategies:

1. Ivory liquid soap works very well in this experiment
2. For purposes of this experiment, very hard water is any calcium-ion-rich solution with conductivity greater than 1000 µS/cm.  A solution can be prepared by adding Calcium chloride CaCl2, to a sample of local water.
3. It may be helpful to established ranges for soft and hard water before students begin the lab.

Additional Resources for this Lesson:

• The United States Geological Survey (USGS) website has real-time water quality data available by county.  Select “USA Water-Quality Table” under “Predefined display’s, select “County” under  “Group Table By”, and type your county in the "Select sites by number or name." Specific conductance, Temperature, Dissolved Oxygen, pH and the date/time of collection are given.
• The USGS also provides an excellent list of water-quality characteristics on their educational website.

Re-teaching and Enrichment Strategies:

• Have students bring in water samples from their home, or from water sources around their home and have them predict which sources will be hard or soft.  Compare results from class with “expected” values according to the USGS site indicated previously.  Discuss with students why or why not their results are similar.
• What are the implications of hard water?  Besides having to use more soap in the shower, how does hard water impact the community?  Hard water can cause build-up in water pipes and damage equipment.  It can also shorten the life of fabrics.
• Identify minerals and other impurities that exist in your water supply that cause water hardness.
• Distill a small amount of water in order to show students what is in the water they drink and use in their homes.  Makes students know that these impurities are important to their health and that drinking distilled water can be harmful.

Data Collection and Analysis:

HYPOTHESIS:

 

DATA:

	Suds height (cm)	Conductivity (µS/cm)
Distilled water
Very hard water
Tap water

QUESTIONS:

1. Is the tap water hard? Explain how you decided on your answer.
2. Where does your tap water come from? How does that source affect the hardness of the water? 
3. How did the hardnesses of the waters you tested in Part II compare? 
4. Why is each of the waters you tested in Part II as hard (soft) as it is? 

DISCUSSION:

Why does soap create more or less suds in different cities?How is water hardness detected?  What causes water hardness?

*Adapted from: Volz, D., & Sapatka, S. (2000). Middle School Science with Calculators. Beaverton, OR: Vernier Software & Technology.