Two reactions; two pKa's. The pKa for bicarbonate carbonic acid reaction is 6.4 The pKa for bicarbonate carbonate reaction is 10.3 Both pKa's are temperature sensitive. An ideal buffering system has a pKa of 7.4 (normal physiologic pH). Bicarbonate has a pKa of 6.1, which is NOT ideal in normal physiologic conditions. In fact, the pH range of effectiveness is probably 5.1 – 7.1 for the bicarbonate buffer system. Bicarbonate is better described as a CO2 transport mechanism.
When carbon dioxide dissolves, it can react with water to form carbonic acid, H2CO3. H2CO3 can dissociate and give away one or two hydrogen ions to form either a bicarbonate ion (HCO3-) or a carbonate ion (CO3 w/ -2 charge). If dissolved calcium is present, it reacts to form insoluble calcium carbonate (CaCO3) or soluble calcium bicarbonate (Ca(HCO3-)2). If you're testing water samples for environmental health and/or water quality, you may need to calculate bicarbonate concentration. To calculate bicarbonate concentration, you'll first need to find total alkalinity for your sample. Testing total alkalinity is beyond the scope of this article; if you need to know how to do so, the link under 'Resources' provides full instructions. Substitute the equation for carbonate concentration as a function of bicarbonate concentration and pH for the equation for total alkalinity.
The expression for total alkalinity is 2 x total alkalinity = HCO3- + 2 CO3 -2 + OH-. (Note that in chemistry, the brackets around a species refer to its concentration, so HCO3- is the concentration of bicarbonate). The equation for carbonate concentration is CO3 -2 = K2 HCO3- / H+, where K2 is the second dissociation constant for carbonic acid. Substituting this expression will give us 2 x total alkalinity = HCO3- + 2 x ( K2 HCO3- / H+ ) + OH-.
Except where otherwise noted, data are given for materials in their (at 25 °C 77 °F, 100 kPa).Y ( Y N?)Carbonic acid is a with the 2 (equivalently OC(OH) 2). It is also a name sometimes given to of in , because such solutions contain small amounts of H 2CO 3.
In, carbonic acid is described as volatile acid or respiratory acid, because it is the only acid excreted as a gas by the lungs. It plays an important role in the to maintain.Carbonic acid, which is a, forms two kinds of: the and the.
In geology, carbonic acid causes to dissolve, producing, which leads to many limestone features such as and.It was long believed that carbonic acid could not exist as a pure compound. However, in 1991 it was reported that scientists had succeeded in making solid H 2CO 3 samples.