LaMotte ACID RAIN STUDY OUTFIT ARO - Manual (Page 6)

EF FECTS OF ACID PRE CIP I TA TION
EF FECTS ON MA TE RIALS
Acid precipitation can affect many of the materials we depend on every day. The
rusting of metals is an oxidation reaction that is accelerated by the presence of
acidic rain, fog and dew. Corrosion of steel, bronze and copper is increased, affecting
the condition and maintenance costs of buildings, bridges, and vehicles. Acid rain
hastens the natural weathering of marble, limestone and mortar. These substances
are composed of calcium carbonate (CaCO
3
) which reacts with sulfuric acid in acid
rain to become water, carbon dioxide, and powdery gypsum. The durability of paints
and textiles are also affected. In many areas, rain water is used for drinking purposes.
The pH of water must be carefully adjusted to make it non-corrosive before it is
circulated in plumbing systems that contain metal components so that metals will
not enter drinking water.
EF FECTS ON STREAMS, PONDS AND LAKES
A healthy, productive freshwater lake has a pH of about 8, slightly basic. The pH
level is maintained at a steady level by the presence of “buffering” chemicals in the
water, primarily carbonate and bicarbonate ions. The buffering chemicals in a
stream, pond or lake are an indication of the types of soils, minerals and rocks in the
area. In some areas, borate (BO
3
_ 3 ), phosphates (PO
4
- , HPO
4
- , and H
2
PO
4
- ), and
silicates contribute to the buffer system. The amount of basic buffering materials in
the water is termed the “alkalinity” of the water. The “alkalinity” of water does not
refer to pH but rather the ability to resist pH changes (buffering capacity).
The presence of these buffering materials helps to neutralize acids as they are added
to or created in the water ecosystem. If a body of water has an abundance of these
buffering materials (high alkalinity), it is more resistant to changes in pH. If a body
of water has very little buffering material (low alkalinity), it is very susceptible to
changes in pH.
As increasing amounts of acids are added to ponds and lakes, their buffering capacity
is consumed. If additional buffering material can be obtained from surrounding soils
and rocks, the alkalinity level may eventually be restored. However, a temporary loss
of buffering capacity can permit pH levels to drop to levels harmful to life in the
water.
An entire season of acid precipitation can be stored up in the form of snow and ice.
Areas which receive a lot of snowmelt each spring are especially susceptible to the
seasonal loss of buffering capacity.
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TESTING THE pH OF HOUSE HOLD PROD UCTS
Test the pH of a number of household products that are readily available from your
home or school. For solutions which are not highly colored, the pH test can be
made without any preparation of the sample. Substitute a sample of the colorless
material for the water sample in the procedure above.
Solutions which are cloudy or colored may be filtered or diluted with distilled water
before the pH test is performed. (Distilled water is unbuffered and will not
significantly affect the pH of a strong sample.)
Use the chart in the preceding section to identify the pH of the solution.
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