# What happens when limestone comes in contact with an acid? Why?

Apr 25, 2018

The limestone dissolves to form a salt (in the chemical sense), water, and carbon dioxide.

#### Explanation:

Limestone is mainly composed of calcium carbonate.

In chemistry, acids and metal carbonates react to form a metal salt, water and carbon dioxide.

$2 {H}_{\left(a q\right)}^{+} + C {O}_{3 \left(s\right)}^{2 -} \to {H}_{2} C {O}_{3 \left(a q\right)} \to {H}_{2} {O}_{\left(l\right)} + C {O}_{2 \left(g\right)}$

So with, for example, hydrochloric acid and calcium carbonate,

$2 H C {l}_{\left(a q\right)} + C a C {O}_{3 \left(s\right)} \to C a C {l}_{2 \left(a q\right)} + {H}_{2} C {O}_{3 \left(a q\right)} \to C a C {l}_{2 \left(a q\right)} + {H}_{2} {O}_{\left(l\right)} + C {O}_{2 \left(g\right)}$

Which results in calcium chloride, water and carbon dioxide being formed.

Since everything that is produced is either a liquid, a gas, or soluble salt, which ends up simply evaporating or flowing off as runoff, the former insoluble limestone rock will appear to dissolve and erode

FYI, the ${H}_{2} C {O}_{3 \left(a q\right)}$ I showed, carbonic acid, which is found in seawater, can also erode limestone, in the same way, albeit more slowly than stronger acids like hydrochloric acid, and thus is one of the ways coastal erosion occurs (corrosion / solution).