When carbon dioxide (CO2) is combined with water, it enter a so called equilibrium which results in the formation of free hydrogen ions (H+). The equilibrium equation is the following CO2 + H2O←→ HCO3- + H+.
The acidity in the body is measured by pH, which is calculated using the concentration of free hydrogen ions (H+). The higher the concentration of the latter, the more acidic the compound is.
In the case of carbon dioxide (CO2), the concentration of free hydrogen ions (H+) increases due to this equilibrium, therefore carbon dioxide is acidic in the body.
