Students
will conduct a series of experiments to simulate water filtration
and purification techniques; these will also be linked to
conditions of water (man-made or natural). The experimentation
will provide concrete, practical exposure to issues of the
availability of clean drinking water, and the different processes
involved to make water safe for human consumption.
Conduct the Apple Analogy to demonstrate availability
of potable freshwater:
cut _ out of the apple - this represents land on earth (set
aside), while the remaining _ represents water on earth
remove peel from the _ portion - this represents the 3%
of water on earth as freshwater (the remainder is saltwater
in oceans, set it aside)
split the peel into 3 parts - this represents the _ of freshwater
not frozen in polar ice caps. Set remaining _ of peel aside.
examine the "freshwater peel" - not even all of this 1%
of the earth's water is potable (safe for drinking) - some
is contaminated by pollution
wrap up: pose question: What can we do to conserve the
precious freshwater we can access? (responses should include:
water conservation, pollution controls, water treatment/purification)
Note: This activity can be done as a teacher demonstration
or in groups of students.
Conduct water filtration/purification experiments.
divide students into small groups (3-4 students); have groups
rotate through various stations or have each group perform
the same experiment simultaneously.
Remind students to follow directions carefully, make
careful observations (e.g., by taking notes and sketching
results), and follow established safety requirements/procedures.
once all groups have conducted experiments, discuss class
results, discuss alternate methods of water treatment/purification
(e.g., chlorination), and speculate if this water is now potable.
Experiment 1: Filtration (removal
of sediment):
Measure 500ml (2 cups) of distilled
water into a large graduated cylinder
Add 30 ml (2 tbsp.) of finely crushed
leaves into the water and stir gently.
Record the appearance of the mixture
in the cylinder.
Place a clean piece of screen over a
1000-mL beaker, labelled Beaker A, and spread a piece of cheesecloth
(or kitchen cloth) over the screen
Pour the mixture slowly through the filter
(make sure it goes through both layers) into the beaker
Observe the liquid in the beaker and
the solid on the filter and record.
Repeat steps 1-6 using Beaker B and a
piece of cotton fabric placed over the screen. Make sure you rinse
the screen in between.
Repeat steps 1-6 using Beaker C and a
coffee filter placed over the screen. Make sure you rinse the
screen in between.
Compare the results of Beaker A, B and
C.
Experiment 2: Filtration (removal
of sediment):
Repeat steps 1-9 using sand instead
of crushed leaves
Experiment 3: Desalination (removal
of salt) - A solar still:
Measure 500ml (2 cups) of distilled water
into a graduated cylinder and pour into a shallow bowl or basin.
Add 30 ml (2 tbsp) of salt and stir until
the salt is dissolved.
Observe the solution in the bowl and record.
Position the tripod over the center of
the bowl.
Stretch the vapour barrier over the tripod
and tape in place so that each side is free of wrinkles.
Place a small bowl under each of the 3
corners of the tripod.
Position the grow light at least 30 cm
(12") above the apparatus.
Leave the apparatus for an hour.
Observe what happens as the salt water
begins to condense and record.
Observe the water that collects in the
smaller bowls (smell, taste) and record.
Compare the properties of the 2 mixtures.
Note: In this experiment, students could taste
and smell the salt solution in order to observe all properties.
This should be done properly, noting to students that tasting materials
is done in rare situations.
Experiment 4: Desalination (removal of salt)
- freezing and straining:
Measure 500ml (2 cups) of distilled water
into a graduated cylinder.
Add 30 ml (2 tbsp) of salt and 3 drops
of red food colouring.
Stir until the salt is dissolved.
Observe and record the properties of the
mixture (Mixture 1).
Pour the solution into an ice cube tray
(or another shallow container).
Place the container in a freezer until
the mixture has a slushy consistency (this may take upwards of
3 hours)
Position a clean sieve over a large empty
beaker and pour the slush into the sieve.
Observe and record the properties of
the mixture in the sieve (Mixture 2).
Leave it to drain into the beaker for
20 minutes.
Observe and record the properties of the
mixture in the beaker (Mixture 3).
Compare the properties of the 3 mixtures.
Note to teacher: prepare steps 1-6 in advance
in order to make effective use of class time
Extensions:
Research procedures for
filtering and purifying water - salt water, polluted water, etc.
Based on research, develop a report listing and describing different
water filtration/purification methods.
Organize a field trip to
a local water purification plant.
View the film Erin Brockovich
, which dramatizes the true story of how unsuspecting residents
in a small California desert town suffer the serious health-related
side effects of contamination by chromium 6 in their soil and
their drinking water. Check copyright before showing this to your
class.
Assessment
/ evaluation:
Observation
checklist (participation and teamwork)
Lab
skills: following directions, observing, and analyzing
