Question

How does carbon dioxide change the acid-base condition of a solution?

Answer 1

The presence of carbon dioxide will increase a solution's acidity because of the formation of carbonic acid.

When carbon dioxide dissolves in aqueous solution, it reacts with water to form carbonic acid, `H_2CO_3`, a weak acid.

`CO_(2(g)) rightleftharpoons CO_(2(aq))`

and

`CO_(2(aq)) + H_2O_((l)) rightleftharpoons H_2CO_(3(aq))`

The carbonate acid will then release either one or both of its protons, producing bicarbonate, `HCO_3^(-)`, and carbonate, `CO_3^(-)`, ions, at the same time increasing the concentration of hydronium ions and making the solution more acidic.

`H_2CO_(3(aq)) + H_2O rightleftharpoons HCO_(3(aq))^(-) + H_3O_((aq))^(+)`

`HCO_(3(aq))^(-) + H_2O_((l)) rightleftharpoons CO_(3(aq))^(2-) + H_3O_((aq))^(+)`

This is essentially the process responsible for ocean acidification.

Read more on that here:

http://www.pmel.noaa.gov/co2/story/Ocean+Acidification