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Exploring techniques to filter water. |
· Analyzing why water cycle is a natural filtration system. VOCABULARY: · solvent· condensation · evaporation · precipitation · water cycle MATERIALS: · Giving Water a Second Chance by J. R.Blueford · Funnels · Beakers · Sand (coarse and fine) · Dirt from garden BACKGROUND:
Water is our most common
natural resource. It is essential to the biology and chemistry of
all living things, it plays a major role in shaping the earth and is an
active agent in many physical reactions. It is important to most life to
keep it clean.
Water exists in three
states of matter: solid (ice), liquid (water), and gas (vapor) at
normal conditions. Water is a colorless, odorless, tasteless liquid
with a melting point of 0° centigrade and a boiling point of 100°
centigrade.
PROCEDURE:
1.
Discuss
with students the following major points about water or the hydrologic
cycle. Draw the diagram of the water cycle.
Goal of this section is for students to see a variety of ways that the
water cycle naturally purifies water through evaporation, transpiration
and infiltration.
A.
Water precipitates from
clouds as rain, snow, sleet, or hail to the Earth’s surface.
B.
Depending on a number of
factors such as soil type, slope, moisture conditions, and intensity of
precipitation will either infiltrate into the ground or runoff into rivers
and streams.
Infiltrate means the water sinks into the ground.
C.
Virtually no water
infiltrates through paved roads and parking lots, so almost all of it
becomes urban runoff. Runoff from rivers, and streams is
stored in large bodies of water such as lakes, estuaries, and oceans.
D.
Water is returned to the
atmosphere evaporation from the surface of land or water bodies, or
through plants by a process called transpiration.
E.
Clouds are formed by
condensation of water vapor that evaporated from the land or
oceans.
2.
Hopefully this diagram should be familiar to students and they should be
able to tell you about each of the components. Ask them which are
human-made portions of the water cycle? (Reservoir, dams and canals.)
Where does a spring get its water supply? (Usually from the ground
water percolating up.) Where does water from the mountains wind up?
(The oceans.) Which is the newest water? (Rain) Oldest? (Oceans.)
3. Read
“Give Water a Second Chance”
so students can see how the water cycle has been cleaning water for eons
of time, but now people can clean it also with different methods. Do
experiments with filtering dirty water using a cotton ball, cotton ball
with course sand and a cotton ball with fine sand.
(for cleanup, at end of lesson be sure to dump dirty sandy water in
the garden, not down the sink). A. Give students a beak with about 150 ml of water, mix in about 5 ml of “dirt” from the school ground and stir to make dirty water.
B. Use
funnels and put a cotton ball in the base of the funnel so it sticks part
way into the funnel part. C. First have the student just pour dirty water into the funnel with the cotton ball and see how much is “cleaned”
D. Make another dirty mixture and repeat the experiment but use 75 ml
of the course sand on top of the cotton ball.
E. Make more dirty water and
this time use a cotton ball in the filter and add 75 ml of fine sand.
Did one work better than another?
F. Then
have them re-pour the water from the last filtration over the fine
sand again to see if they can filter it even more. (does the water get
even clearer?) G. Set out coarse sand, fine sand and more cotton and some powdered clay. Set the students free to experiment to try to figure out how to get the cleanest most filtered water. For example, they can try layering the sands and clay, or pour dirty water through multiple times.
H. Discuss
results with students. How did
they get the cleanest water?
Go back to the diagram of the water cycle and have them note infiltration
has water going through deep dirt and rock deposits.
Filtration produces very clean water but it takes a long
time. Sometimes 100s of years!
We should never waste water!
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