1.8 Investigating Matter: Foul Water
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 procedures: oil–water separation, sand filtration, and charcoal adsorption and
filtration. Before starting, read the procedure to learn what you will need to do, note safety precautions, and plan
necessary data collecting and observations.
Before starting, read the procedure to learn what you will need to do, note safety precautions, and plan necessary
data collecting and observations.
Procedure
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3.
Use the data table provided to record your observations throughout the investigation
Using a clean beaker, obtain approximately 100 mL (milliliters) of foul water from your 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.
Describe in detail the appearance, color, clarity, and odor of your original sample. Record your observations in
the “Before treatment” row of your data table.
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.
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Allow your sample to sit in the graduated cylinder for at least one minute.
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.
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.
Read and record the volume of the liquid sample remaining in the gradated cylinder.
Dispose of the liquid in the test tube as directed by your teacher.
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 too large to fit between sand
grains—from a liquid.
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Using a straightened paper clip, poke small holes in the bottom of a disposable cup. See Figure 1.5 in your
textbook.
Add pre-moistened gravel and sand layers to the cup (The bottom gravel layer 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.)
Gently pour the sample to be filtered into the cup. Catch the filtrate in a beaker as it drains through.
Dispose of the used sand and gravel according to your teacher’s instructions. (Caution: Do not pour any sand or
gravel into the sink!)
Observe the properties of the filtered water sample and measure its volume. Record your results. Save the
filtered water sample for the next procedure.
Charcoal Adsorption and Filtration
Charcoal adsorbs, which means attracts and holds on its surface, many substances that could give water a bad taste,
a cloudy appearance, or an odor.
14. Fold a piece of filter paper, as shown in Figure 1.7 in your textbook.
15. Place the folded filter paper in a funnel. Hold the filter paper in position and moisten it slightly so that it rests
firmly against the base and sides of the funnel cone.
16. Place the funnel in a clay triangle supported by a ring, as shown in Figure 1.8 in your textbook. Lower the ring so
that the funnel stem extends 2 to 3 cm (centimeters) inside a 150-mL beaker.
17. Place no more than one level teaspoon of charcoal in a 125-mL or 250-mL Erlenmeyer flask.
18. Pour the water sample into the flask. Swirl the flask vigorously for several seconds. Then gently pour the liquid
through the filter paper. Keep the liquid level below the top of the filter paper; liquid should not flow between
the filter paper and the funnel because that might permit unwanted charcoal and other solid matter to seep
into the filtrate.
19. If the filtrate is darkened by small charcoal particles, once again filter the liquid through a clean piece of
moistened filter paper.
20. When you are satisfied with the appearance and odor of your charcoal-filtered water sample, pour the filtered
water sample into a graduated cylinder. Record the final volume and properties of your purified sample.
21. Follow your teacher’s suggestions about saving or disposing of your purified sample. Place the used charcoal in
the container that is provided for that purpose.
22. Wash your hands thoroughly before leaving the laboratory.
Data Analysis
Record all calculations and answers in the space provided.
1.
What percentage of your original foul water sample did you recover as purified water? This value is called the
percent recovery.
Percent recovery
__________
2.
What volume of liquid (in milliliters) did you lose during the entire purification process?
Volume lost
__________
3.
What percent of your original foul-water sample was lost during purification?
Percent lost
__________
To answer the following questions, first collect a list of percent recovery values for water samples from each
laboratory group.
3.
Construct a histogram showing the percent recovery obtained by all laboratory groups in your class. To do so,
organize the 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, as illustrated in Figure 1.9 of your textbook.
4.
What was the largest percent recovery obtained by a laboratory group in your class? What was the smallest?
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?
Largest percent recovery __________________________
Smallest percent recovery __________________________
Range of percent recovery __________________________
5.
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.
Average percent recovery
__________
6.
The mean is a mathematical expression for the most “typical” or “representative” value for a data set. Another
useful expression is the median value, or middle value. To find the median for percent-recovery data, list all
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. 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 of your class laboratory results?
Median percent recovery
__________
Data Table
Data Table
Volume
(mL)
Before
Treatment
After
oil-water
separation
After sand
filtration
After charcoal
adsorption
and filtration
Color
Clarity
Odor
Presence
Presence
of Oil
of Solids