The pH of a freshly prepared 0.1 M aq. solution of sodium bicarbonate is 8.3 at 25 ºC. It can be expected to remain rather stable if the solution is kept in a nearly full closed container. If the solution is left in open container or is somehow aerated, its pH tends to decrease while the atmospheric CO2 dissolves in the solution, being then chiefly ruled by the carbonic acid (H2CO3) / sodium bicarbonate (NaHCO3) buffer system. However, this solution only reaches equilibrium with the atmospheric CO2 partial pressure for a lower pH than that specified (8.0). Therefore, it is not expected to be stable for pH = 8.0. It could be stabilized at the specified pH if the solution could be aerated by a bubbling air stream of controlled (decreased as required) CO2 partial pressure.