Question

How does acid rain form?

Answer 1

Acid rain forms when water reacts with sulfur dioxide or nitrogen dioxide.

Explanation:

Acid rain forms when water molecules in the atmosphere react with sulfur dioxide or nitrogen oxides to form an acidic compound. The resulting compound has a lower pH.

The chemical reactions that occur when water molecules mix with sulfur dioxide and nitrogen dioxide are below:

Nitrogen oxides can be produced naturally by lightening strikes and sulfur dioxides is formed when volcanoes explode, but acid rain can also be caused by emissions due to humans.

Answer 2

Sulfur oxides and nitrogen oxides reacting with water.

Explanation:

SULFUR OXIDES

1) Sulfur dioxide `("SO"_2)` is produced industrially from the combustion of sulfur-containing fossil fuels and smelting of sulfide ores

`"S"(s) + "O"_2(g) -> "SO"_2(g)`

2) Sulfur dioxide `("SO"_2)` is then oxidized by sunlight to form sulfur trioxide `("SO"_3)`

`2"SO"_2(g) + "O"_2(g) -> 2"SO"_3(g)`

3) The oxides react with water to form acids

`"SO"_2(g) + "H"_2"O"(l) -> "H"_2"SO"_3(aq)`

`"SO"_3(g) + "H"_2"O" (l) -> "H"_2"SO"_4(aq)`

NITROGEN OXIDES

1) Nitrogen monoxide `("NO")` is produced from internal combustion of engines

`"N"_2(g) + "O"_2(g) -> 2"NO"(g)`

2) Nitrogen monoxide `("NO")` oxidizes to form nitrogen dioxide

`2"NO"(g) + "O"_2(g) -> 2"NO"_2(g)`

3) Nitrogen dioxide reacts with water to form nitric acid `("HNO"_3)` and nitrous acid `("HNO"_2)`

`2"NO"_2(g) + "H"_2"O"(l) -> "HNO"_3(aq) + "HNO"_2(aq)`

or it reacts with oxygen and water and becomes nitric acid

`4"NO"2_(g) + "O"_2(g) + "H"_2"O"(l) -> 4"HNO"_3(aq)`

The above was taken from Oxford IB Chemistry Study Guide by Geoffrey Neuss textbook (pg 62)