Filtered or Not Filtered That's the Question!

Pre-lesson Instructions (30 minutes prep time)

• Students should work in groups of 3 or 4.

• Write the names of the 7 different filtering materials on 7 individual small slips of paper and place them in a hat or basket. In addition, write “free choice” on several small slips of paper. Add enough “free choice” slips for each group to choose a total of 3 filtering materials (suggested option).

You may also place the materials as a "store" and students have a certain price range they can use for the store.

• Gather materials for this activity. Each filtration material needs to fill the water filtering system to a depth of 5–8 cm. There should be enough of each filtration material for several groups to use. Make sure to have extra material for students to choose their “free choice” options.

• Wad up enough coffee filters for multiple groups to use as a filtration layer (You may leave this out and have the filters in the store setting making them develop this strategy on their own).

• Rinse the activated charcoal granules in advance to remove the dust. Put the granules in a mesh bag (pantyhoses work well) and rinse with tap water.

Note: To increase rigor, you may give them the contaminated water and bottle filter base. All other materials will be used by each determining group. This allows for higher thinking and creative skills.

Filtering system structure: (one per group)

• Punch a hole in the top of each cup, just below the rim to avoid a vacuum (optional). * Use this diagram.
• Remove the labels on the 2-liter bottles and then cut off the bottom of the bottle, just above the curve of the bottle.
• Construct the structure of the water filtering system by covering the mouth of the bottle with at least 10 layers of cheesecloth and secure with a rubber band.

To increase rigor, you may allow the students to determine how to place and use the filter design in their groups independently. 

Make “Contaminated Water”:

• Test your tap water before making the contaminated water solution. You want to start this solution with “clean water." Your clean water should have a pH between 6.5 and 7.5. If your tap water is not between pH 6.5 and 7.5, then use store-bought drinking water.
• Mix 1 part Italian salad dressing (vinegar and oil with seasonings, shaken) to 5 parts water in a large, clean container.
• Make enough contaminated water for each group to have about 500 ml.
• Note the pH of the contaminated water, it should be around 4. If needed, you can add vinegar to the contaminated water to drop the pH.

Note: Reserve enough clean water (either tap water or store-bought drinking water with a pH between 6.5 and 7.5) so that each student group has about 500 ml. 

Instructional Procedure

1. Remind students about pH including base, neutral, and acid. Also reference pH testing using litmus paper and pH color charts.

2. Review the problem with the students.
Problem: What can I do to make clean water?

3. Pass out a copy of Observation and have the students read and discuss in their groups.

4. Encourage your students to discuss and make observations about this topic by completing the first two columns in the KWL (KNOW/WANT TO KNOW/LEARNED) chart in their journals. Use the KWL chart to help students organize prior knowledge, identify interests, and make real-world connections. As students suggest information for the “KNOW” column, ask them to share “How they have come to know this information.”

6. Allow your student groups time to develop a Hypothesis relating to this activity and the “problem question." 
7. Students will test their hypothesis following this procedure.

Students

1. Put on your safety glasses.
(Stress the importance of keeping eye protection on during this lesson.)

2. Place the bottle upside down with its mouth over the clear plastic cup to catch the filtered water.  Make sure the cup underneath the system is large enough to “catch” the water to be filtered through.

3. Choose three slips of paper from the teacher.
Allow each group to choose three slips of paper with designated filtering materials or “free choice” written on them.

The items written on these papers will be the materials you layer in your water filter. If you choose a “free choice” slip, you and your group may choose what material to use for
this filtration layer.

OR

Give students an objective: Their town's water supply is contaminated after a storm. It is their mission to develop a filtration system. The filter must be able to allow water to run through and deposit into the cup. 

Note: This is where you may limit direct instruction and allow creativity. You may also allow the "store" concept to replace the above distribution technique.

Students

4. Gather your filtration materials on the paper plates; one on each plate. As a group, decide the order in which to layer your materials.

5. Fill the bottle with the first filtering material to a depth of 5–8 centimeters (cm).
Note: Coffee filters and cotton balls will need to be packed down.

6. Place the second filtering material to a depth of 5–8 cm on top of the first one.

7. Place the third filtering material to a depth of 5–8 cm on top of the second filtering
material.

8. Obtain 350 ml of clean water. Observe the properties of the water before you filter it. Use the wafting technique to smell the water. Measure the pH of the water with litmus paper and compare it to the pH color chart. Collect data and record your observations. Remember smelling rules in the science lab and do not taste. This pH measurement will serve as the control.

Note:

When filtering the contaminated water, students will know the contaminated water is cleaned when it matches the control pH.

9. Run the clean water through your water filtering system to make sure it will allow water to flow through. Students should run approximately 10-16 oz. of clean water through their water filtering system to make sure it will allow water to flow through. Make sure the cup underneath the system is large enough to “catch” all the water passing through.

OR

Allow students to experiment and determine if their design will work.

10. While you are waiting for the clean water to run through the water filtering system, draw and label your diagram to match your filtration system. (this can be skipped and allow students to work without determining if the filter works)

11. Once the clean water has gone through the water filtering system, replace the clear plastic cup with a new one. If the water is sandy, it should be disposed of outside. Otherwise, it can be disposed of in the sink. The cup can be reused in the next step.

12. Get 350 ml of contaminated water. Observe the properties of the water before you filter it. Check the odor of the water. Measure the pH of the water with litmus paper and compare it to the pH color chart. Collect data and record your observations.

Remind students to use the wafting technique to smell the water. They should also measure the pH of this water sample. Go over the rules of the science lab regarding smelling and tasting.

13. Run the contaminated water through your water filtering system. Observe the properties of the water after it has been filtered once and record your observation.

Measure the pH of the water with litmus paper and compare it to the pH color chart. Collect data and record your observations. Remind students the rules of the science lab regarding smelling and tasting.

14. Replace the clear plastic cup with a new one. Pour the filtered water back into the water filtering system.

15. Filter the water again. While the contaminated water is running through the water filtering system, discuss in your group what each layer in your filtration system did to the water.

16. Observe the properties of the water after it has been filtered for the second time. Check the odor of the water. Measure the pH of the water with litmus paper and compare it to the pH color chart. Collect data and record your observations. Remind students the rules of the science lab regarding smelling and tasting.

17. After taking all measurements, study the data and draw conclusions by answering the questions.

Make sure the students compare the properties of their filtered water to the control (clean water) to determine if their contaminated water was “cleaned” by their water filtering system. Using this information, ask students to determine if the data supports or refutes their hypothesis.

18. Dispose of all material by wrapping in newspaper and placing the material in a trash receptacle.

Conclusion
• Discuss the answers to your set questions.
• Have the students update the LEARNED column in their KWL chart.
• Ask students how their findings relate to the development of new water filtration systems and recycling for space exploration?
• Ask students “What do you wonder now?” and encourage students to design their own experiments.