CHEMISTRY LAB: ACID RAIN
(ACIDRAIN.DOC)
Name: ______________________
Date: _______________________
1. Introduction: Higher levels of acidity in rainfall (and snowfall) can be directly
correlated with increasing emissions of sulfur and nitrogen oxides into the atmosphere.
These compounds are released by man's activities when so-called “fossil fuels,” coal and
substances separated from petroleum, are burned in automobile and truck engines, power
plants, steel mills, factories, and homes. When the oxides of sulfur and nitrogen combine
with water vapor in the atmosphere, they form a variety of acids including sulfuric acid,
sulfurous acid, and nitric acid. Studies show about 65% of the additional acid in "acid
rain" above the natural levels is sulfuric acid, 30% is nitric acid, and 5% is other.
SO2 + H2O  H2SO3 (sulfurous acid)
SO3 + H2O  H2SO4 (sulfuric acid)
The ecological effects of precipitation containing these and other acids depend not only
on the acidity of the rainfall but also on the buffering capability of the soil. Soils that are
rich in lime (CaO) demonstrate a natural protection against acid rain. In this experiment,
you will investigate the chemical properties of several laboratory prepared acid rain
samples and examine the effect of soil on the acid rain.
2. Safety: Wear your apron and goggles while working in the lab.
3. Equipment and Materials Required:
a. From the prep area:
long-stemmed filter funnel, with two pieces of filter paper to fit
small container of powdered calcium oxide (CaO)
small container of “lime-free soil”
six small pieces of calcium carbonate (grain-of-rice size)
six pieces of magnesium ribbon, each 5 mm long
plastic forceps (to handle the small samples above)
pH probe with interface equipment, or handheld pH meter, or pH paper
50-ml sample of “Adirondack Mountain acid rain” (carry in your beaker)
thin-stemmed polyethylene pipets containing the following:
“Scotland acid rain”
Port Orange rain
distilled water
b. From your lab station supply cupboard:
one 250-ml beaker
one 100-ml beaker
two 50-ml beakers
25-ml graduated cylinder
c. From your lab station equipment drawer:
ringstand support ring, size small
scoopula
d. At your lab bench:
centigram balance
ringstand, medium sized
distilled water wash bottle
e. Laboratory apron and safety goggles for each member of your lab group.
4. Procedure:
a. Put on your lab apron and safety goggles.
b. Using the larger wells of the micro-reaction plate only, place 10 drops of one
of the four water samples in each of three different wells. Use pH paper or a pH meter in
the first well to determine the pH of this sample. Refer to Attachment 1 for the correct
procedures for using the pH meter. Be sure to rinse it between samples with distilled
water to avoid contamination of one sample by another. Record your results in the data
table below.
c. In the second well, place a small piece of magnesium ribbon (about 5 mm
long). Observe and record the results in the data table. Dispose of solids in the school
trash can and not down the drain.
d. In the third well, place a small piece of calcium carbonate (about the size of a
piece of rice). Observe and record the results in the data table. Dispose of solids in the
school trash can and not down the drain.
e. Clean out the plate, rinse with distilled water, and repeat these three tests with
the second water sample. Repeat for the third and fourth water samples as well.
f. Set up a ringstand with a small ring to support a long-stemmed funnel for
gravity filtration. Fold the filter paper in half twice and open it so three thicknesses are
on the same side, thus making a cone. Place this in the funnel and dampen it with
distilled water to cause it to relax and cling tightly to the funnel. Position a 100-ml
beaker to catch the filtrate. Place the long side of the diagonally cut tip against the inside
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wall of the beaker so the filtrate can run down the side of the beaker instead of dripping
in the middle and splashing filtrate out of the beaker.
g. Place 3 grams of lime-free soil in the filter. Pour 20 ml of “Adirondack
Mountain acid rain” onto the soil and let it pass through the filter and into the beaker
below. Test the filtrate as you did the first four samples and record your results in the
data table.
h. Dispose of the soil and the filter into the trash. Rinse out your equipment with
distilled water and set it up again exactly as before. In the 250-ml beaker, thoroughly
mix 0.1 g of calcium oxide powder with 3 grams of the lime-free soil. Place this
modified soil in the filter as before and again pour 20 ml of “Adirondack Mountain acid
rain” onto the soil. Collect and test this filtrate as before. Record your results in the data
table.
i. Dispose of this soil sample as before. Wash all your equipment with tapwater.
Rinse your glassware with distilled water and shake off the excess before returning it to
the cupboard. Clean up your bench with a damp sponge and rinse it out as well. Fold
and return your apron. Return your goggles to the sterilizer cabinet. Rinse your hands
before leaving the lab.
5. Data and Observations:
DATA TABLE
Water tested:
pH:
Reaction with Mg:
Reaction with
CaCO3:
“Adirondack
Mountain acid rain”
“Scotland acid rain”
Port Orange
rainwater
Distilled water
“Adirondack Mt.
acid rain” filtered
through “lime free
soil”
“Adirondack Mt.
acid rain” filtered
through soil with
lime added
6. Analysis and Conclusions:
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a. How did the addition of lime affect the pH of the filtered rainwater?
_______________________________________________________________________
b. Predict what would happen if more calcium oxide were used with the soil.
_______________________________________________________________________
c. How did the acidity of our local rainwater compare with the (laboratory
prepared) samples of acid rain?
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
d. Write a balanced equation showing the reaction of magnesium ribbon with
sulfuric acid in the acid rainwater.
________________________________

________________________________
e. Write a balanced equation showing the reaction of calcium carbonate with the
sulfuric acid in the acid rainwater.
________________________________

________________________________
7. Questions:
a. Write the word equation and the symbol equation for the formation of
sulfurous acid from sulfur dioxide and water vapor.
_______________________________________________________________________
_______________________________________________________________________
b. Write the word equation and the symbol equation for the formation of sulfuric
acid from sulfur trioxide and water vapor.
_______________________________________________________________________
_______________________________________________________________________
c. What is the major source of atmospheric oxides of nitrogen and sulfur?
_______________________________________________________________________
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d. What three properties of rainwater did you examine in this experiment?
_______________________________________________________________________
e. Explain how soil type can change the effects of acid rain.
_______________________________________________________________________
f. In your own words, write the purpose of this experiment.
_______________________________________________________________________
_______________________________________________________________________
8. Extension:
a. Use the Internet or a reference book and attach a map of the U.S. to the back of
this page showing the pH of the rainwater or other forms of precipitation by area. Give
your source.
b. List ten common household or garden plants, bushes, or trees, and the
recommended soil pH range which is recommended for their propagation. Give your
source.
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
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(PLACE YOUR MAP FOR PARAGRAPH 8a ON THIS PAGE)
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ATTACHMENT 1
USING THE pH PROBE WITH A COMPUTER
1. Carefully remove the probe from the bottle of storage solution by unscrewing the cap.
Roll the O-ring down and off the pH probe. Remove the bottle cap from the probe. Set
these aside to use when putting the probe away when you are done.
2. Connect the pH probe to any interface device provided and plug that interface, in turn,
into the computer as directed by the teacher.
3. Turn on the display and the computer. Run Windows and Logger Pro. Use File, Open
and choose the experiment file for pH vs. time. Opening that file adapts the computer to
recognize and interpret the signals coming in as pH readings and display them
appropriately.
4. Although we could calibrate these probes to certain solutions of known pH for more
accurate results, for what we are doing here the generic calibration file in the software
will give us results close enough. Immerse the probe in some tapwater and it should read
about 7.6. Always rinse the probe with distilled water before placing it in the next
solution to avoid contamination, but do not try to read the pH of distilled water itself.
Sitting in distilled water is too hard on these probes. Be gentle with them, keep them
moist, and generally upright (wire at the top).
5. Click on Collect to begin collecting readings, and you get an idea of how rapidly they
respond and how stable they are. You may stir gently with them for a few seconds to
hurry things along, but you should let them sit perfectly still to get a final reading. When
the graph and table fill up, clicking on Collect again will clear out that data and start over,
so write down your data.
6. Make sure you have made all the measurements before shutting down. Rinse out your
glassware with tapwater first, and then a final rinse with distilled water.
7. When you are done, Exit Logger Pro without saving, and Exit Windows. Turn off the
computer.
8. Finally, when you intend to put the pH probe away, rinse it and replace the bottle cap
and O-ring without damaging the sensor on the end of the probe. Place the probe tip back
in the storage solution and tighten down the bottle cap snugly.
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ATTACHMENT 2
INSTRUCTIONS FOR USING THE
HAND-HELD pH METERS
1. To use the instrument, remove the protective cap and immerse the tip of the electrode
in the solution to be measured. Try to immerse about 2.5 cm of the probe into the
solution to be measured, but you can use less as long as the whole bulb at the tip is
immersed. If the bulb is dry, soak the tip in tapwater for a few minutes. Never immerse
the probe up to the widened part or beyond: if water gets in the threaded connector, the
probe will be damaged. The red top area contains the electronics and two batteries, and is
not waterproof. Be very careful not to get even a drop of water into the switch on top.
2. Do not be alarmed if white crystals form around the protective cap. This is normal
and they will disappear when rinsed with water. Between solutions and after use, rinse
the tip of the electrode with distilled water to minimize contamination. Store the
electrode with a few drops of electrode storage solution (or tap water if none is available).
Never use deionized or distilled water to store the electrode. Do not try to measure the
pH of distilled water.
3. Limitations:
Range: 0.00 to 14.00
Resolution: 0.01
Accuracy: +/- 0.2
Calibration: two points
Operating Temperature Range: 0 to 50 Celsius
Battery Life: 3000 hours (2 x 1.4 volts)
4. Bring the pH meter to the teacher if the display is weak or will not come on when you
use the switch on top of the unit. It may need new batteries.
5. When you are done, rinse the tip area one more time with distilled water and slip on
the protective cap. Switch off the electrical power.
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LAB TIPS:
1. Solution preparation:
“Adirondack Mountain acid rain” is dilute sulfuric acid. Try for a pH of 4.5.
“Scotland acid rain” is dilute sulfuric acid. Try for a pH of 3.
Port Orange rain is just that, or a dilute sulfuric acid. Try for a pH of 5.5.
distilled water is just that.
“lime free soil” can be silica sand, but not Florida beach sand, which contains remnants
of seashells.
2. Labels:
“Adirondack
Mountain
acid rain”
“Adirondack
Mountain
acid rain”
“Adirondack
Mountain
acid rain”
“Adirondack
Mountain
acid rain”
“Adirondack
Mountain
acid rain”
“Adirondack
Mountain
acid rain”
“Adirondack
9
Mountain
acid rain”
“Adirondack
Mountain
acid rain”
“Adirondack
Mountain
acid rain”
“Scotland
acid rain”
“Scotland
acid rain”
“Scotland
acid rain”
“Scotland
acid rain”
“Scotland
acid rain”
“Scotland
acid rain”
“Scotland
acid rain”
“Scotland
acid rain”
“Scotland
acid rain”
“Scotland
acid rain”
Port
10
Orange
rain
Port
Orange
rain
Port
Orange
rain
Port
Orange
rain
Port
Orange
rain
Port
Orange
rain
Port
Orange
rain
Port
Orange
rain
Port
Orange
rain
Port
Orange
rain
distilled
water
11
distilled
water
distilled
water
distilled
water
distilled
water
distilled
water
distilled
water
distilled
water
distilled
water
distilled
water
lime free
soil
lime free
soil
lime free
soil
lime free
soil
lime free
soil
lime free
soil
12
lime free
soil
lime free
soil
lime free
soil
lime free
soil
lime free
soil
calcium
oxide
(CaO)
calcium
oxide
(CaO)
calcium
oxide
(CaO)
calcium
oxide
(CaO)
calcium
oxide
(CaO)
calcium
oxide
(CaO)
calcium
oxide
(CaO)
calcium
13
oxide
(CaO)
calcium
oxide
(CaO)
calcium
oxide
(CaO)
14