Question

Which reaction accounts for the fact that the pH of rain is naturally slightly acidic?

a. CO2 + H2O = H+ + HCO3-
b. NO2 + H2O = 2 H+ + NO3-
c. SO3 + H2O = 2H+ + SO42-
d. Ca2+ + CO2 + H2O = CaCO3 + 2H+

Answer 1

The reaction involving CO2 and H2O forming H2CO3, which dissociates into H+ and HCO3-, is responsible for the natural acidity of rain. Acid rain, which is more acidic than normal rain, can occur when additional nonmetal oxides are present and form stronger acids.

Step-by-step explanation:

The reaction that accounts for the fact that the pH of rain is naturally slightly acidic is CO2 + H2O = H+ + HCO3-. When carbon dioxide (CO2) dissolves in water (H2O), it forms carbonic acid (H2CO3), which then dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). This process is natural and contributes to the normal acidity of rainwater, which has a pH between 5 and 6.

Although carbon dioxide is naturally present in the atmosphere and contributes to the acidity of rain, other nonmetal oxides like sulfur dioxide (SO2), sulfur trioxide (SO3), nitrogen oxide (NO), and nitrogen dioxide (NO2) can dissolve in rainwater and cause the formation of stronger acids like sulfuric acid and nitric acid, leading to acid rain with a pH of less than 5.