Carbonate Curve

This graph shows the relationship between three related molecules (H₂CO₃, HCO₃^-, and CO₃^2-) and pH. The curves on the graph, show how much of each molecule is present in water at a specific pH. Changing the pH (you can do this by dragging the red bar), changes the amount of each molecule that is in the water.

Alkalinity is a measure of how much acid buffering capacity a system has. That capacity is equal to the amount of H⁺ ions the system can absorb - so in this system, it is equal to the HCO₃^- concentration plus two times the CO₃^2- concentration (because CO₃^2- can absorb two H⁺ ios).

Move the red line to various parts of the graph and convince yourself of the relationship. When done, continue on to the Chemistry of Acidificaiton