GEOCHEMISTRY QUESTION please help with the process I have no idea how to do this

Question

GEOCHEMISTRY QUESTION please help with the process I have no idea how to do this. a. calculate the ksp for magnesite at 25*C. b. what is the solubility of magnestie in pure water? How much difference does it make if it is assumed that activity equals concentration versus activity calculated from the Debye-Huckel equation?( in order to answer the latter part of the question you will have to calculate the final solibulity by successive approximation. Use the original ion concentrations to determine ionic strength , then determine the activity coefficeints. Use the coefficients to recalcutate the ion concentraions. Repeat this process until there is no change in the activity coeffiecnts) c. Mg2+ and Co3- form the complex MgCO3(aq). For this complex K stab= 10^2.98. How does the existance of this complex effect the solubility of magnesite ? A numerical answer is required.

Explanation / Answer

Answer:

a. Ksp of magnesite at 25 oC

pKsp = 8.03

pKsp = -log[Ksp]

So,

Ksp = 9.33 x 10^-9

b. solubility of Mgnesite in pure water

Ksp = [Mg2+][CO3^2-]

9.33 x 10^-9 = x^2

solubility = x = 9.66 x 10^-5 M

for the later part, we need concentrations.

c. For MgCO3 Kstab= 10^2.98

Mg2+ + CO3^2- <==> MgCO3   Kstab

Solubility,

MgCO3 <==> Mg2+ + CO3^2- Ksp

Ksp/Kstab = 9.33 x 10^-9/10^2.98 = 9.77 x 10^-12

So, the solubility = sq.rt.(9.77 x 10^-12) = 3.12 x 10^-6 M

Solubility would reduce by the presence of MgCO3(aq) in solution for magnesite.

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