with in the solution according to {| width="500" | style="width:50%; height:25px;"| | Ka2 = at 25 °C |} is known as the bicarbonate ion. Calcium bicarbonate is many times more soluble in water than calcium carbonate—indeed it exists only in solution. Some of the combines with in solution according to {| width="500" | style="width:50%; height:25px;"| | Ka1 = at 25 °C |} Some of the breaks up into water and dissolved carbon dioxide according to {| width="500" | style="width:50%; height:25px;"| | Kh = at 25 °C |} And dissolved carbon dioxide is in equilibrium with atmospheric carbon dioxide according to {| width="500" | style="width:45%;"| = kH | where kH = 29.76 atm/(mol/L) at 25 °C (Henry constant), P being the partial pressure. |} For ambient air, P is around atmospheres (or equivalently 35 Pa). The last equation above fixes the concentration of dissolved as a function of P, independent of the concentration of dissolved . At atmospheric partial pressure of , dissolved concentration is moles per liter. The equation before that fixes the concentration of as a function of concentration. For [] = , it results in = moles per liter. When is known, the remaining three equations together with {| width="450" | style="width:50%; height:25px;"| | K = 10−14 at 25 °C |} (which is true for all aqueous solutions), and the fact that the solution must be electrically neutral, i.e., the overall charge of dissolved positive ions must be cancelled out by the overall charge of dissolved negative ions , make it possible to solve simultaneously for the remaining five unknown concentrations (note that the previously mentioned form of the neutrality is valid only if calcium carbonate has been put in contact with pure water or with a neutral pH solution; in the case where the initial water solvent pH is not neutral, the balance is not neutral). The adjacent table shows the result for and (in the form of pH) as a function of ambient partial pressure of (Ksp = has been taken for the calculation). At atmospheric levels of ambient the table indicates that the solution will be slightly alkaline with a maximum solubility of 47 mg/L. As ambient partial pressure is reduced below atmospheric levels, the solution becomes more and more alkaline. At extremely low P, dissolved , bicarbonate ion, and carbonate ion largely evaporate from the solution, leaving a highly alkaline solution of calcium hydroxide,