Name:
Lab Partner(s):
Period:
Date:
Lab 7: Foul Water
INTRODUCTION
Your objective is to purify a sample of “foul water,” producing as much “clean water” as possible.
You will use three water-purification procedures: (1) oil-water separation, (2) sand filtration, and (3)
charcoal adsorption/ filtration. In filtration, solid particles are separated from a liquid by passing the
mixture through a material that retains the solid particles. The liquid collected after filtration is called
the filtrate.
EQUIPMENT
From lab bench:
100-mL graduated cylinder
250-mL beaker
100-mL Erlenmeyer flask
large funnel
ring stand
iron ring
clay triangle
From kit:
tubing and pinch clamp
filter paper
paper clip
1 Tbs charcoal
sand
gravel
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PROCEDURE
1. Obtain 100 mL of foul water. Record the volume in your data table. (Your teacher has already
measured the volume; no need to re-check)
2. Examine the properties of your sample: color, clarity, odor, and presence of oily or solid regions.
Record your observations in the “Before treatment” section of your data table.
Oil-Water Separation
As you probably know, oil and water don’t mix very well; instead, two
layers form. Which layer floats on top of the other? You will make
observations during the following procedure to check your answer.
3. Place a funnel in a clay triangle supported by a ring and ring stand (see
figure). Attach a rubber tube to the funnel tip as shown.
4. Close the rubber tube by tightly pinching it with the metal pinch clamp.
Gently swirl the foul-water sample for several seconds to suspend the
solids. Then immediately pour about half the sample into the funnel.
BE CAREFUL NOT TO SLOSH OVER THE FUNNEL EDGE! Let
The liquid stand for a few seconds in the funnel until the liquid layers
separate. (Gently tapping may encourage oil droplets caught in the
funnel stem to break free.)
250-mL
beaker
5. Carefully open the tube, slowly releasing the lower liquid layer into an
empty 250-mL beaker. Just as the lower layer has drained out, quickly
close the rubber tube.
6. Drain the remaining (upper) layer into a paper cup.
7. Repeat Steps 4-6 for the other half of your sample, adding each liquid to the correct beaker.
8. Which beaker contains the oily layer? ____________________Which layer is smellier?
9. Dispose of the oil layer in the trash. Observe the properties of the remaining layer, measure its
volume, and record on the Data table. Save this water sample for the next step.
Sand Filtration. A sand filter traps and removes solid impurities—at least those particles too large to
fit between sand grains—from a liquid.
10. Using a straightened paper clip or pencil, poke small
holes in the bottom of a paper cup. Add gravel and
pre-moistened sand layers to the cup as shown. (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 into the cup).
11. Gently pour the liquid sample to be filtered into the
prepared cup; use a stirring rod to guide flow. Catch the filtrate (filtered water) in a clean 250-mL
beaker as it drains through.
12. Observe and record the properties of the filtered water sample and measure its volume.
Charcoal Adsorption/Filtration. Charcoal adsorbs (attracts and holds on its surface) many
substances that could give water a bad taste, odor, or cloudy appearance.
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13. Fold a piece of filter paper as shown. Place the folded filter in a funnel and wet it slightly so it
clings to the inside of the cone. BE CAREFUL NOT TO TEAR THE WET FILTER PAPER.
14. Place the funnel in a clay triangle supported by a ring clamp. Lower the ring clamp so the funnel
stem extends 2-3 cm inside a 100-mL beaker.
15. Add about one tablespoon of charcoal to your water sample, stir, then let it sit for 2 minutes with
occasional stirring. Pour the water sample into the flask. Swirl vigorously for a few seconds.
Then gently pour the liquid through the filter paper. KEEP THE LIQUID LEVEL BELOW THE
TOP OF THE FILTER PAPER!
16. If the filtrate is darkened by small charcoal particles, refilter the liquid through a clean piece of
moistened filter paper.
17. When you are satisfied with the appearance and odor of your water sample, pour it into a graduated
cylinder. Record the final volume and properties of the purified sample.
18. Test the conductivity of your purified water, as directed by your teacher.
Cleanup
19. Dispose of liquids down the drain, solids in the trash. Place dirty glassware in dishpan, get clean
replacements from your teacher. Wash your hands before leaving the lab.
Name:
Lab Partner(s):
Period:
Date:
Lab 7: Foul Water
PRE-LAB QUESTIONS
1. What three water purification techniques will you use?
2. Define “filtrate”.
3. After you separate the oil and water layers,
a. what will you do with the oil portion?
b. what will you do with the water portion?
4. If your filtrate has bits of charcoal in it, what do you do?
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DATA:
Foul Water Observations
Volume,
ml
Color
Clarity
Odor
Presence of
Oil
Presence of
Solids
Before
treatment
After oilwater
separation
After sand
filtration
After
charcoal
and
filtratn
Results of Conductivity Testing:
Calculations:
1. What percent of your original foul water sample did you recover as purified water?
% of water recovered =
volume of water purified
x 100 =
volume of foul water sample
2. What volume of liquid did you lose during purification?
3. What percent of your original foul water sample was lost during purification?
Data Analysis
1. What were percent recovery data of all lab groups in your class?
2. Construct a histogram showing percent recovery obtained by all lab groups in your class. (Graph
paper on last page of this packet.)
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3. What was
a. the largest percent recovery obtained by a lab group?
b. the smallest?
c. What is the range of percent recovery?
4. What was the mean percent recovery?
5. What was the median percent recovery?
Questions
1. Is your “purified water” sample “pure” water? How do you know?
2. Suggest how you might compare the quality of your water sample with that of other lab groups.
That is, how can the relative success of each group be judged?
3. How would you improve the water-purification procedures you followed so that a higher percent of
purified water could be recovered?
4. Estimate the total time you expended in purifying your water sample:
a. In your view, did that time investment result in a large enough sample of sufficiently
purified water?
b. In the real world, it is often said that “time is money.”
i. If you spent twice as much time in purifying your sample, would that extra
investment in time “pay off” in higher-quality water?
ii. If you spent about ten times as much time? Explain.
5. Municipal water-treatment plants do not use distillation to purify the water. Why?
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