24. a. Calculate the Ksp for magnesite MgCO) at 25°C. Use the thermodynamic dat

Question

24. a. Calculate the Ksp for magnesite MgCO) at 25°C. Use the thermodynamic dat from Appendix II, source 2, for this calculation. b. What is the solubility of magnesite in pure water? How much difference does ic make if it is assumed that activity equals concentration versus activity calculated from the Debye-Hückel equation? (Note: In order to answer the latter part of the question, you will have to calculate the final solubility by successive approximak tions. Use the original ion concentrations to determine the ionic strength, then determine the activity coefficients. Use the coefficients to recalculate the ion concentrations. Repeat this process until there is no change in the activity coefficients.) Hi! I need help with part B. What are the steps to using successive approximation to solve this? I already found that Ksp=102.5 and that l=0.0 with an I value of 0.0121M the activity Coeff are.67 for Ma2+ and.64 for (CO3)2- 121M and I used the Debye-Hückel to find that

Explanation / Answer

Solution:

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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