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Calcium carbonate

In this situation, the dissociation constants for the much faster reactions

H2CO3 ⇌ H+ + HCO
3
⇌ 2 H+ + CO2−
3

allow the prediction of concentrations of each dissolved inorganic carbon species in solution, from the added concentration of HCO
3
(which constitutes more than 90% of Bjerrum plot species from pH 7 to pH 8 at 25 °C in fresh water).[54] Addition of HCOHCO
3
⇌ 2 H+ + COHCO
3
(which constitutes more than 90% of Bjerrum plot species from pH 7 to pH 8 at 25 °C in fresh water).[54] Addition of HCO
3
will increase CO2−
3
concentration at any pH. Rearranging the equations given above, we can see that [Ca2+] = Ksp/[CO2−
3
]
, and [CO2−
3
] = Ka2 [HCO
3
]
/[H+]
. Therefore, when HCO
3
concentration is known, the maximum concentration of Ca2+ ions before scaling through CaCO3 precipitation can be predicted from the formula: