Section: Science
82)
Acid rain, more properly known as acid precipitation, is a man-made environmental problem that is known to be escalating. The source of acid rain is oxides of sulfur and nitrogen that dissolve in water, lowering the pH to such an extreme that damage to living and nonliving things results. Often the source of acid rain is pollutants from factories or automobiles. The gases produced by fuel combustion react with water vapor in the air and produce acids such as sulfurous acid, sulfuric acid, and nitrous acid. Burning of coal, oil, and natural gas is especially likely to cause an increased amount of acid rain. In addition to man-caused sources of acid rain, volcanic eruptions and some bacterial decay also produce these acidic oxides which lower the pH of water.
Scientists measure the acidity of an object using the pH scale. The scale ranges from 0 to 14, with a pH of 7 being considered neutral. A pH less than 7 is acidic and one more than 7 is basic or alkaline. Normal rain has a pH of about 5.6. It is not neutral because rainwater naturally dissolves a small amount of carbon dioxide from the air and becomes slightly acidic.
Acid rain becomes a serious problem when the pH of the precipitation becomes less than 3.5. There have been reported pH of 1.3 in some areas. These extremely acidic conditions kill fish and plants, and may render lakes and soil totally uninhabitable. Young fish not only are killed by such acidic waters, but any fish that may survive are usually not able to reproduce. Sometimes, nature provides a means of neutralizing these acidic waters via naturally alkaline ammonia compounds or calcium compounds such as limestone,
The table below gives the pH of some common substances:
| pH | Substance |
| 1.1 | Battery acid |
| 2.8 | Household vinegar |
| 5.5 | Normal rainwater |
| 7.0 | Distilled water |
| 8.2 | Baking soda |
| 11.6 | Household ammonia |
| 13.9 | Lye |
Which of the following mineral formations would be most effective at neutralizing acid rain?
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Explanation
The passage specifically mentions calcium compounds as being natural neutralizers of acid rain.
