17.99 The solubility of CaCO_3 is pH dependent, (a) Calculate the molar solubili

Question

17.99 The solubility of CaCO_3 is pH dependent, (a) Calculate the molar solubility of CaCO_3 [K_y = 4.5 times 10^-9) neglecting the acid-base character of the carbonate ion. (b) Use the K expression for the CO^2_3 ion to determine the equilibrium constant for the reaction If we assume that the only sources of Ca^2-, HCO_3, and OH ions are from the dissolution of CaCO_3, what is the molar solubility of CaCO_3 using the equilibrium expression from part (b)? (d) What is the molar solubility of CaCO_3 at the pH of the ocean (8.3)? (e) If the pH is buffered at 7.5, what is the molar solubility of CaCO_3?

Explanation / Answer

Answer (a)

Molarity . . .CaCO3(s) . .==> . .Ca2+(aq) . .+ . .CO3 2-(aq)

If we neglect acid base charecter of carbonate ion.

Initial . . . . . . . . . . . . . . . . . . . . .0 . . . . . . . . . . .0

Change . . . . . . . . . . . . . . . . . . .x . . . . . . . . . . .x

Final . . . . . . . . . . . . . . . . . . . . .x . . . . . . . . . . .x

Ksp = [Ca2+][CO3 2-] = (x)(x) = x^2 = 4.5x 10^-9

x = 6.7082 x 10^-5 M = molar solubility of CaCO3

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