Students will perform a series of hands-on experiments to learn the
four steps of purifying water—screening, sedimentation, filtration, and
chemical treatment.
At each step of the process, they will take a sample of water and place a piece of potato in it.
After several days, students will observe the potato slices in the five
water samples to record the amount of bacterial growth present.
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| Objectives |
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1) Students will be able to list and describe the four steps for purifying water for public use.
2) Students will record their observations in a lab notebook and draw a graph showing the amount of bacterial growth in the five samples.
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| Materials |
Copies of experiment observation sheet
Tank with polluted water from lesson 1
For each lab group:
Tank with polluted water from lesson 1
Household strainers
5 - 250mL beakers
Filter with one layer of pebbles, one layer of sand, one layer of charcoal. A long stemmed funnel lined with filter paper should be placed below the layered filtering funnel.
Dissecting microscope
Chlorine
Rulers
5 - Potato slices
Masking tape
Markers
Eye droppers
5 - Petri dishes
Tweezers
Graph Paper |
| Procedure |
1) Ask students to list the four steps of water purification that were discussed during the last lesson.
2) Explain that today students are going to do a series of experiments
with potato slices to see how much bacterial growth accrues on the
potato after each step of the purification process.
3) Divide students into 4 groups of 4-5 students.
One
member of each group should come to the front of the room and get the
strainer, beakers, filter, chlorine, and potato slices.
4) On the blackboard, write the instructions for the experiment:
a) Label five beakers with the following labels: unpure water, screened
water, sedimented water, filtered water, and chemically treated water.
b) Place one potato slice at the bottom of each beaker
c) In the beaker labeled ‘unpure water’ put 200 mL of water from the polluted water tank from lesson 1 over the potato slice.
d) Take another 1000 mL of the dirty water and pour it into the strainer over the beaker labeled ‘screened water’.
e) Remove 800 mL from the screened water beaker and place it in the beaker labeled ‘sedimented water’.
Let the water sit for 15 minutes.
f) After 15 minutes, remove 600 mL from the sedimented water beaker using your pipette.
Be careful not to disturb the bottom of the beaker.
Pour this water into the filter and place the end of the filter over the beaker labeled ‘filtered water’.
g) Remove 300 mL of the filtered water and pour it into the beaker labeled ‘chemically treated water.’
Add 3 drops of chlorine to the beaker using your eye dropper.
5) Let the beakers sit in a cool place with indirect sunlight for 48-72 hours.
6) After 48-72 hours, instruct students to label 5 petri dishes with the same labels as the beakers.
7) Students should use their microscope to examine each of the 5 samples.
They should remove the potato slices from the beaker and put it into the appropriate Petri dish.
How much bacterial growth do they observe in each sample?
They should complete the ‘Experiment Summary Sheet’ with their observations.
8) At the end of the lesson, ask students to share their observations.
Which sample had the most growth?
Which had the least?
What kinds of materials were removed at the different steps?
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| References |
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Review the steps of water purification using Wikipedia, the online encyclopedia.
Available at
http://en.wikipedia.org/wiki/Water_purification
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| State
Standards |
1.1.2- The student will modify or affirm scientific ideas according to accumulated evidence.
1.2.5- The student will select appropriate instruments and materials to conduct an investigation.
1.2.6- The student will identify appropriate methods for conducting an investigation (independent and dependent variables, proper controls, repeat trials, appropriate sample size, etc.).
1.4.1- The student will organize data appropriately using techniques such as tables, graphs, and webs (for graphs: axes labeled with appropriate quantities, appropriate units on axes, axes labeled with appropriate intervals, independent and dependent variables on correct axes, appropriate title).
1.4.5- The student will check graphs to determine that they do not misrepresent results.
1.5.1- The student will demonstrate the ability to summarize data (measurements/observations).
1.5.2- The student will explain scientific concepts and processes through drawing, writing, and/or oral communication.
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| Lesson Resources |
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