At pH = 7.0 calcium carbonate is water insoluble. Calcium carbonate has a solubi

Question

At pH = 7.0 calcium carbonate is water insoluble. Calcium carbonate has a solubility of 14 mg/L

CaCO3(s) + H2O(l) <==> Ca2+(aq) + CO32-(aq) Equilibrium lies towards left-side at pH = 7.0 (general equation). The solubility increases by a factor of five in presence of carbon dioxide as shown by a reaction as below.

H2O (l) + CO2 (g) => H2CO3(aq)

CaCO3 (s) + H2CO3 (aq) => Ca(HCO3)2 (carbon weathering) CaCO3 solubility greatly increased here.

And the total reaction mechanism:

CaCO3 (s) + CO2 (g) + 2H2O (l) => Ca2+ (aq) + 2 HCO3- (aq) => Ca(HCO3)2 The product is calcium hydrogen carbonate. These are very complex reactions.

At low pH:

H+(aq) + Ca(HCO3)2 <==> Ca2+(aq) + H2O (l) + CO2(aq) and H+(aq) + CO32-(aq) <==> HCO3-(aq)

acidity regulated now, calcium bicarbonate adjusts pH. At low pH protons (H+) are dominant and are neutralized by bicarbonate.

At high pH:

OH-(aq) + Ca(HCO3)2 <==> Ca2+(aq) + H2O (l) + CO2(aq) [Apply HCO3- <==> H+(aq) + CO32-(aq)] and

[ H+ (aq) + OH-(aq) => H2O(aq)]; [CO32- (aq) + H2O(l) <==> HCO3-(aq) + OH-(aq)]

at high pH hydroxyl ions are dominant and are neutralized by protons from bicarbonate.

Finally the bicarbonate-carbonate system acts as a buffer to mainatain specific pH region values. Our blood is also pH regulated by this bicarbonate-carbonate system.

Hope i have been successful in explaining the basic concept.

Thank You So Much! Please Rate this answer as you wish.

Explanation / Answer

Explain the effect carbonate has on the solubility of calcium ions in natural waters. Show the general reaction. (ii) How is this effect different at low and high pH?

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