PROBLEM:
Is the pH of acid rain changed as it passes through
soil?
Acid
rain, more correctly acid deposition, is largely the consequence of burning of
fossil fuels. The oxides of
nitrogen and sulfur released from fuel combustion form various acids in the
atmosphere that fall out of the air as dry deposition or as a component of rain,
snow, or fog. The effects of this
are widespread, from the damage to monuments and car paint to the decline of
aquatic ecosystems.
Fortunately,
the effects on agricultural crops have been negligible; however forest trees
appear to be more susceptible to injury from acid deposition.
The degree of injury to plants and to aquatic organisms is dependent upon
the nature of the soil and parent rock where they live and grow.
In certain areas soils may contain carbonate which buffers against
acidification. This experiment examines that process and uses it as a first step
for the further study of acid rain.
MATERIALS:
Coffee
filters, garden soil, coarse sand, pH test strips or pH meter
Acidified
distilled water (one cup of vinegar added to one pint of water), rain water or
melted snow, strainer into which filters fit, pelleted limestone or limestone
dust.
PROCEDURE:
1.
Collect
and label soil samples. About 3
cups of soil should be collected from test sites.
Ideally samples should come from different locations and habitats.
Ideal sites might gardens, woods, hillsides, stream sides, and athletic
fields, and so on. Commercial
potting soils could also be sampled. Dry
the samples and remove any large rocks, roots and so on.
2.
Place a
coffee filter into the strainer
3.
Put one
cup of dry soul sample into the filter.
4.
Pour one
cup of acidified distilled water through that soil and collect the filtrate in a
beaker or plastic cup. Gently press
on the filter so that most of the water is removed from the sample.
5.
Measure
the pH of the filtrate.
6.
Repeat
this process with all the samples and with the sand. Use a new coffee filter for each test.
7.
Mix about
1/4 cup of limestone into 1 cup of the dried soil and sand.
8.
Repeat
the tests with each of the limestone added samples.
9.
Measure
the pH of the acidified distilled water and of plain distilled water.
1.
Construct
a table or bar graph showing the data collected from all soil samples.
2.
Explain
why the pH values of the two sets of data (without and with limestone added) are
different.
3.
Describe
any differences in the pH of the filtrates collected from the soil and sand
samples. Offer an explanation for
the differences if any.
4.
How many
times more acidic is the acidified distilled water than the plain tap water?
WEB
SITES:
http://www.plugged-in.org/what_is_acid_rain4.html
http://www.marketplaceforthemind.state.pa.us/m4m/lib/m4m/documents/labs/Acid_Rain_and_Soils.pdf
http://www.chem4kids.com/files/react_acidbase.html
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Environmental/acidrain/CAA.html
http://www.epa.gov/air/sect812/r-140.html
http://www.scar.utoronto.ca/%7Eweather/maryp/Effects/fish.html