Question

Why do CaCO3 + CO2 + H2O form Ca(HCO3)2?

Answer 1

Is it because CO2 + H2O create the carbonic acid H2CO3 and it somehow reacts with CaCo3?

- Considering poor solubility of CaCo3(s) a probable.

Explation; Calcium Carbonate is poorly soluble in pure water (47 mg/L) kept = 3.7×10-9 to 8.7 × 10-9 at 25°C there exist on ionic equilibrium with the ions formed due to ionization of soluble calcium carbonate.

CaCo3(s) <=> Co3(so ln) <=> (aq) 2-

+Co3(aq)

Now in presences of Co2 in water H2Co3 is formed and as a result medium become acidic.

In this acidic medium there exists.

- 2-

HCo3 ion and H+ . The Co3 (aq)ions get protonatal by this H+ ions and HCo3 ions are formed 2-

so, decrease I concentration of Co3(aq)ions in solution shifts the above equilibrium toward right and dissolution of more CaCo3(3) in solution takes place.