Question

The solubility of CaCO3 is pH-dependent.
Ka1(H2CO3)=4.3×10^−7
Ka2(H2CO3)=5.6×10^−11

a. Calculate the molar solubility of CaCO3 (Ksp = 4.5×10^−9) neglecting the acid-base character of the carbonate ion.

b. Use the Kb expression for the CO3^2− ion to determine the equilibrium constant for the reaction
CaCO3(s) + H2O(l) ⇌ Ca2^+(aq) + HCO3^−(aq) + OH^−(aq)

c. If we assume that the only sources of Ca2+, HCO3−, and OH− ions are from the dissolution of CaCO3, what is the molar solubility of CaCO3 using the preceding expression?

d. What is the molar solubility of CaCO3 at the pH of the ocean (8.3)?

f. If the pH is buffered at 7.5, what is the molar solubility of CaCO3?

Answer 1

See you other post above. I assume for parts c and f that we consider only k1 for H2CO3 since k1 and k2 are widely separated.