Foul Water
Your objective for this lab is to clean a sample of foul water, producing as much “clean water” as possible, to a point
where you could use it for hand washing (You will not test any samples by taste). In this experiment you will be
designing your own procedure using the materials provided, as well as any equipment in your lab drawer. Materials that
will be provided include filter paper, gravel, sand, decolorizing charcoal, Styrofoam cups, and paper clips.
In this experiment, you will be designing your own procedure for purifying your sample of water. To prepare for making
your own procedure, read through the descriptions of each technique provided, as well as think about other techniques
you may be able to perform with the provided materials.
Separation Techniques
Oil-Water Separation
As you probably know, if water and oil are mixed and left undisturbed, the water and oil
do not noticeably dissolve in each other. Two distinct layers form (See Figure 1). If your
sample has two layers, you must decide which layer is the water layer, and which is not
aqueous (dissolved in water). The layers must then be separated and the water layer
must be retained for further purification.
Figure 1 Water-oil mixture
showing layers
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 filtered is called the
filtrate. A sand filter traps and removes solid
impurities- at least those particles that are too
large to fit between sand grains- from a liquid.
Figure 2 shows how to prepare the sand
filtration apparatus using the Styrofoam cup,
sand, gravel, and a paper clip. One tip for
setting up the apparatus is to poke the holes
in the cup from the inside of the cup to get
slightly better water flow. Figure 2 shows the
holes being poked from the outside.
Figure 2 Setup for sand filtration
Charcoal Adsorption and Filtration
Charcoal adsorbs, which means attracts and holds on its surface,
many substances that could give water a bad taste, cloudy
appearance, or an odor. Forces in action here are adhesive forces,
which are attractive forces between molecules of different
substances. Many substances that cause water to have a bad taste, a
cloudy appearance, or an odor have stronger adhesive forces with
charcoal than they do with water. Charcoal adsorption takes
advantage of the fact that these contaminants stick to the charcoal
and can be removed.
Paper Filitration
This is the most common method of filtration and is used to remove
an insoluble solid material from a solution. A filter paper is folded
(conventional or fluted) and placed in a filter funnel which is then
placed in the neck of an Erlenmeyer flask or supported in a clamp or ring stand. The solution to be filtered is then slowly
and carefully poured into the funnel taking care not to fill the funnel above the edge of the filter paper.
Procedure
Before coming to class on the day of the lab, it is your responsibility to have read through these techniques and come up
with a procedure on your own for purifying your sample of water. When you get to class, you will be given 5-10 minutes to
get with your lab partner to compare procedures, and come up with one together that you both agree on. Keep in mind
that you only have one class period to perform the lab, so collaborate quickly. Your procedure will then be approved by
the teacher to make sure it is safe enough to perform. Once your procedure is approved your lab group will be given
approximately 100 mL sample of foul water. You will perform your procedure, and once you believe your water is clean
enough, it will be tested for conductivity with a conductivity tester. During your procedure, you will be required to find the
density of your sample (Density=mass/volume) before starting, as well as after each step of the purification. In your
notebook you should note the density and any numbers needed to calculate the density, as well as any and all
observations, both qualitative and quantitative, you make throughout the experiment.
Safety
Students will wear safety goggles to protect their eyes from accidental splashes.
Lab Notebook Report Format
 Title
 Purpose
 Safety
 Procedure Day 1 (Step by Step)
 Data for Day 1,
o Qualitative Observation
 Results of Sample Analysis
 Conductivity
 Appearance
 Tyndall Effect
 Quantitative Observations – make sure you include the measurements needed to calculate the
density of your original foul water and your “clean” sample.
 Density Calculations – include correct units and significant figures
o Original Foul water sample
o “Clean” water sample after purification
o Picture of Day 1 Set-Up (You may use your phone to take a picture and then print it off and add it to the
end of your lab report)
 Procedure Day 2 (Step by Step)
 Data for Day 2
o Same information at Day 1
o Picture of Day 2 Set-Up (You may use your phone to take a picture and then print it off and add it to the
end of your lab report)
 Analysis Questions - Answer with complete sentences, you do not have to write the question.
o What percent of your original foul water sample did you recover as purified water (percent recovery)?
o What volume of liquid (in milliliters) did you lose in the entire purification process
o What percent of your original foul water sample was lost during purification?
o Were the densities different after each step? If so, what accounted for the differences? If not, why would it
be the same?
o How successful was each step of your procedure?
o Is your water pure? How can you tell?
o When taking measurements, how many decimal places did you read and record for each instrument?
o Did these separation techniques cause physical or chemical changes to the sample?
o How could you improve the water-purification procedures you followed so that you could recover a high
percent of purified water?
o Estimate the total time you spent purifying your water sample.
o In your opinion, did that time investment result in a large enough sample of sufficiently purified water?
 Conclusion/Summary
o What did you think about the lab?
What did you like/dislike?
Suggestions/Comments