Bicarbonate H2CO3 hydrogen ions

One such buffer substance commonly employed in living organisms is carbonic add (H2CO3), which is weakly dissociated into hydrogen ions and bicarbonate ions (neglecting the H3O+ complex actually formed) ... 

Sweet Corrosion. It is caused by the presence of dissolved COj in the prodnced llnids. CO2 reacts with water to form carbonic acid (H2CO3), which dissociates to form hydrogen ions and the carbonate ion. At the anodic sites, the metal atoms give np electrons and dissolve to form metal ions. These electrons are taken up by hydrogen ions at cathodic sites to form atomic hydrogen. Bicarbonate ions, however, react to form a protective iron carbonate film, and the rate of corrosion depends on the stability of this film [2]. The corrosion mechanism can be represented by the sketch shown in Figure 11.7. 

H2CO3 > H+ + HCO3 Carbonic acid > hydrogen ion bicarbonate... 

Notice that when hydroxides accept hydrogen ions, water is always the product. Water is not a product in the cases of ammonia, the carbonates, and the bicarbonates. However, in the case of carbonates and bicarbonates, water often does ultimately form. The carbonic acid, H2CO3, in Equations 12.20 and 12.21 is unstable and will spontaneously decompose into water and carbon dioxide. This reaction is often acconpanied by vigorous gas (COj) evolution and will be discussed in more detail in Section 12.7. 

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