alleryStart learning →What pH marks rainwater as acid rain rather than as normal rain?
AA pH above 7, since rain is usually basic
BA pH between 5 and 6, the usual rain range
CA pH above 6, which is unusual for rainfall
DA pH below 5, which is under the usual range
Answer & Solution
Correct answer: D. A pH below 5, which is under the usual range
1. Even clean rain is mildly acidic because dissolved carbon dioxide forms carbonic acid.
2. That gives normal rainwater a pH somewhere between 5 and 6.
3. Rain is called acid rain when its pH drops below 5.
4. The extra acidity comes from oxides of sulfur and nitrogen forming sulfuric and nitric acids.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.2 pH and pOH_
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