Carbon Dioxide Equilibrium

When solutions are in equilibrium with carbon dioxide, its solubility and thus its concentration is determined by Henry's law. If the partial pressure of CO2 is higher, so must be its solubility. The plot of logarithm of concentrations versus pH for the various carbonate species will have a constant horizontal line for CO2 (as its equivalent H2CO3). The concentrations of other species will change with pH as shown in the figure.

When the pH changes, carbon dioxide dissolves or escapes to form or dissipate the bicarbonate and carbonate needed to satisfy their equilibria. Remember this is an equilibrium diagram, and that the curves shown are for after the reactions are completed.

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