PG 9
Name: ____________________________
Date: ___________
Foul Water Lab
Teacher: _____________________
Period: ______
Introduction
Your objective is to clean up a sample of foul water, producing as much “clean water” as possible, to a
point where it could be used for hand-washing. (Caution: Do not test any water samples by drinking or
tasting them.) You will use several different water-purification processes: oil-water separation, sand
filtration, and charcoal absorption and filtration.
Before starting, read the procedures to learn what you will need to do, note safety precautions,
and plan necessary data collecting and observations.
Before you begin:
1. Using a clean beaker, obtain approximately 100mL (milliliters) of foul
water from you teacher. Measure its volume accurately with a graduated
cylinder. Record the actual volume of the water sample in your data
table. Leave your sample in the graduated cylinder.
2. Describe in detail the appearance, color, clarity, odor, presence of oil,
and presence of solid. Record your observations in the “Before
treatment” row of your data table.
To find the volume of liquid
in a graduated cylinder,
read the scale at the bottom
of the curved part of the
liquid (meniscus).
Part 1: Oil-Water Separation
As you probably know, if oil and water are mixed and left undisturbed, the oil and water do not
noticeably dissolve in each other. Instead, two layers form. Which layer do you think will float on top of
the other?
Make careful observations in the following procedure to check your answer.
3. Allow the foul water to sit in the graduated cylinder for at least one minute. During this time, any
oily residue should float to the top of the sample
4. Using a clean, dry Beral pipet, carefully remove as much of the upper liquid layer as possible and
place it in a clean dry test tube.
5. Add several drops of distilled water to the liquid you placed in the test tube. Does the water
float on top or sink to the bottom? Is the liquid you removed in Step 5 water? Explain your
reasoning, using evidence from your observations to support your answer.
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6. Observe the properties of your water sample and measure its volume. Record all results in your
table.
Part 2: Sand Filtration
In filtration, solid particles are separated from a liquid by passing the mixture through a material that
retains the solid particles and allows the liquid to pass through. The liquid collected after it has been
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filtered is called the filtrate. A sand filter traps and removes solid impurities – at least those particles
too large to fit between sand grains – from liquids.
7. Using a straightened paper clip poke several small holes in the bottom
of a paper cup.
8. Using a ruler, add pre-moistened gravel and sand layers to the cup as
follows
a. FIRST LAYER: 1 cm of gravel
b. SECOND LAYER: 2 cm of sand
c. THIRD LAYER: 1 cm of gravel
The bottom layer of gravel prevents the sand from washing through
the holes. The top layer of gravel keeps the sand from churning up
when the water sample is poured in.
9. Place your sand filter on top of a clean 100 mL beaker. Gently pour
the foul water through the filter. Catch the filtrate (filtered water)
in the beaker as it drains through.
10. Dispose of the used sand and gravel according to your teacher's
instructions. (Caution: Do not pour any sand or gravel into the sink!)
11. Observe the properties of the filtered water sample and measure its
volume in a clean graduated cylinder. Record all results in your table.
Save the filtered water sample for the next procedure.
Part 3: Charcoal Adsorption/Filtration
Charcoal absorbs, which means attracts and holds on its surface, many
substances that could give water a bad taste, a cloudy appearance, or an odor.
12. Fold a piece of filter paper as shown below.
13. Place the folded filter paper in a funnel. Hold the filter paper in
position and wet it slightly so it clings to the inside of the funnel
cone.
14. Place the funnel in a clay triangle supported by a ring clamp. Lower
the ring clamp so the funnel stem extends a 2 to 3 cm (centimeters)
inside a 100-mL beaker. (See diagram).
15. Place no more than one teaspoon of charcoal in an Erlenmeyer flask.
16. Pour the water sample into the flask. Swirl the flask vigorously for
several seconds. Then gently pour the water sample (with charcoal)
through the filter paper. Keep the liquid level below the top of the
filter paper. Liquid should not flow through the space between the
filter paper and the funnel.
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17. If the filtrate is darkened by small charcoal particles, refilter the liquid through a clean piece of
moistened filter paper.
18. Observe the properties of your water sample and measure its volume in a clean graduated
cylinder. Record all results in your table.
19. Pour the used charcoal in the container provided by your teacher.
20. Wash all glassware, return all materials, and wipe down your lab table. Be sure to wash your hands
before you leave class.
Calculations
1. What percent of your original foul water sample did you recover as purified water? This value is
called the percent recovery.
2. What volume of liquid (in milliliters) did you lose during the entire purification process?
3. What percent of your original foul-water sample was lost during purification?
Graphing
Next we will be constructing a histogram. First, you will need to collect all the percent recovery values
for water samples from every laboratory group.
Your Group: _____
Percent Recovery Values
Group 2: _____
Group 4: _____
Group 6: _____
Group 1: ______
Group 3: _____
Group 7: _____
A histogram is similar to a bar graph. First you need
to organize your data into equal subdivisions, such as
90.0-99.9%, 80.0-89.9%, and so forth. Count the
number of data points in each subdivision then use
this number to represent the height of the
appropriate bar on your histogram. Look at the
example to the right.
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Group 5: _____
Number of lab groups
Complete your histogram in the space provided
Percent Recovery
Data Analysis
1. What was the largest percent recovery obtained by a laboratory group in your class? _______
2. What was the smallest? _______
3. The difference between the largest and smallest values in a data set is the range of those data
points. What was the range of percent recovery data in your class? _______
4. What was the average percent recovery for your class? _______
(Compute an average value by adding all values together and dividing the sum by the total
number of values. The result is also called the mean value.)
5. The mean is a mathematical expression for the most “typical” or “representative” value for a dat
asset. Another useful expression is the median value, or middle value. To find the median for
percent-recovery data, list all the values in either ascending or descending order. Then find the
value in the middle of the list – the point where there are as many data points above as below.
Consider this data set:
If you have an even number of data points, take the average of the two values nearest the middle.
What is the median percent recovery of all your class laboratory results? _______
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Water Purity
1. Your teacher will organize a test of electrical conductivity. This test focuses on the presence of
dissolved, electrically charged particles in the water. You will also compare the electrical
conductivity of distilled water and tap water.
Conductivity of Your Sample
Conductivity of Distilled Water
Conductivity of Tap Water
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_______
_______
What do these tests suggest about the purity of your water sample? (Is it pure or not pure?)
Support your answer with evidence from your observations.
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2. Next, you will test the clarity of the various
water samples by passing a beam of light through
each sample. Observe the results. The
differences are due to the presence or absence of
the Tyndall effect. The particles in the vial on
the right are too small to see, but large enough to
reflect light coming from a beam to the left of
the vials. This is called the Tyndall effect.
Particles in the solution in the vial on the left are
too small to reflect light.
Referring to your observations, explain what this test suggests about the purity of your water
sample.
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Questions
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1. Is your purified water sample pure water? Provide evidence to support your answer.
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2. How could you compare the quality of your final water sample with that obtained by other
laboratory groups? That is, how should we someone judge the success of each laboratory group?
Defend your answer using evidence from this investigation.
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3. How could you improve the water-purification procedures you followed so that you could recover a
higher percent of purified water?
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4. Estimate the total time you spent purifying the water. ______________
5. In your opinion, did that time investment result in a large enough sample of sufficiently purified
water?
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6. It is sometimes said that “time is money.”
a. If you spent twice as much time purifying your sample, would that extra time investment
pay off in higher-water quality?
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b. If you spent about ten times as much time, would that extra investment pay off? Explain
your reasoning.
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