Ask The Science Experts

Acidity (or alkalinity) is measured on a pH scale which is an abbreviation for its “potential for Hydrogen.” The scale measures a substance’s acidity from zero to 14. Zero would be extremely acidic and 14 is not acidic at all (very basic). Of course, 7 is right in the middle of the scale and is neutral.

Any rain with a pH of 5.0 or less is considered acid rain. Normal rain and snow which contains dissolved carbon dioxide has a pH of about 5.6 so it is more basic than acidic. Of course the acidity of rain is very dependent on the geographical area. The rain in a lot of Eastern Europe has a pH of 4.3 to 4.5. The eastern United States and Canada is typically between 4.2 and 4.6. The worst area in North America is around Lake Erie and Lake Ontario and the pH of the rain there is typically about 4.2.

Take a look at some of the common substances below for a comparison:

Substance pH
Sulfuric Acid 1.0
Lemon Juice 2.3
Vinegar 3.3
Acid Rain 4.3
Normal Rain 5.6
Distilled Water 7.0
Human Blood 7.4
Seawater 7.6-8.4

Source: The Handy Science Answer Book.

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