BACKGROUND:
Water is an important resource for
all people in the world. People can die from lack of clean water
to drink. Most students do not think about water because in the United
States it is almost an unwritten rule that cities, counties, states and
the federal government will provide this resource. Early in our country
this was not so. Many people died because the rain did not bring
water or that sewage from a city polluted the waterways. The United
States is aware of the dangers of polluted water and have one of the strictest
laws in the world. Not all nations in this world have water privileges
that Americans have.
The world’s oceans have always been a “dumping”
ground for pollution. In many areas raw sewage and other wastes are
put into the oceans. Many humans see the oceans as such a vast place
that it could never get polluted. But this is wrong. Currents
in the oceans move the pollution away from the land, but it still remains
in the system. Some wastes are sometimes used by plants and animals
in the oceans to help them grow, but too much will upset the natural balance.
There are some substances that will dissolve
and others that will remain in the system. For instance, plastic
will not degrade and remains floating on the world’s oceans. Other
substances like phosphorous (from soaps) can be used by small plants in
the oceans as fertilizer.
Pollution is a term used by the media and
general public frequently. However, most children do not understand
how the word differs from dirty. Pollution is when water (or any
other part of the environment) becomes offensive or harmful to organisms.
Fresh and salt water can become polluted. However, seawater is not polluted
just because it is salty.
Salt water, although not useful to drink by
humans, is not polluted or dirty; it has mineral salts dissolved in it.
This lab has the students think about the difference between dirty, polluted,
and clean water.
PROCEDURE:
- Brainstorm with students
and make a list of polluted and dirty components of water.
POLLUTED: oil, harmful chemicals (like
mercury, lead), too many dead animals, plastic bags, metal
DIRTY: wood, mud, rocks, algae (kelp)
- Each group of students should have two jars
for Exercise I. Students should fill up each jar with 50 ml of water
and mix one with 25 ml of vinegar and the other with 2 ml of sand.
Students should shake the jars and determine which jar is dirty or
polluted. The sand jar is dirty because the sand will settle out,
however, the vinegar cannot be removed easily and the solution is therefore
polluted.
- Pre-mix 5 containers (baby food jars work
well) and have students look at one or two drops of each of the containers
under the microscope. You may want to label each jar as UNKNOWN 1,
UNKNOWN 2, etc. Below are suggested contents:
jar 1 = 1/4 water + soil
jar 2 = 1/4 water + 2 drops of food coloring
jar 3 = 1/4 water + 3 drops of oil
jar 4 = 1/4 water + 3 drops of soap
jar 5 = 1/4 water + salt
- Students should figure out if the
water is polluted or dirty and record the observations on the sheet. Use
the microscope to look at a drop of each of the water to see if students
can identify particles in the water. You must remember that polluted or
dirty water sometimes depends on the type of animal using that water.
What may not be toxic to humans, may be toxic to little animals, or vice
versa. For instance, soap in water is not polluted if we wash our
face, but if we had to drink soapy water it would be polluted. Students
should be encouraged to justify their answers. Consider it correct
if their justification is logical.
