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11 Nov 2019

A Precipitate of CaF2 has been formed in a solution containing 0.025 M NaNO3 and 0.015 M Ca(NO3)2.

(a) Calculate the inonic strength of the solution. (At this point you may neglect the contribution from the ions of the precipitate.)

(b) Using the activity coefficients, calculate the molar solubility of CaF2 in this solution. Thermodynamic Ksp for CaF2=3.9x10-11 (HINT: you will have to carry out an interpolation.)

(c) Verify the assumption in (a): [Ca2+] and [F-] from CaF2 are negligible. If you made any assumptions in (b), verify them as well.

(d) Calculate the mass, in grams, of F- (i.e. the mass of the ion that will be dissolved) that will be in 250.0 mL of this solution at equilibrium.

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Tod Thiel
Tod ThielLv2
16 Apr 2019

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Related questions

Groundwater at a temperature of 250C flows through strata containing abundant fluorite (CaF2) mineralization and becomes saturated with respect to that mineral. The equilibrium solubility product, Ksp, for this reaction is 10^-10.4.

a) Calculate the concentrations of Ca2+ and F- once the water has reached saturation with respect to fluorite assuming that prior to entering the mineralized strata the water had an ionic strength of less than 10-5 mol/L and contained negligible Ca2+ and negligible F-. For this part of the problem, neglect activity corrections. (Note that for each mole of CaF2 that is dissolved, you will get one mole of Ca2+ and two moles of F-.

b) Calculate the ionic strength for the groundwater that has the concentrations of Ca2+ and F- that you determined in part a) assuming that Ca2+ and F- are the only major ions in the groundwater. Then calculate the activity coefficients for Ca2+ and F- at this ionic strength. Were you justified in neglecting activity corrections?

c) Repeat the calculations from part a) but this time including activity corrections for water with the ionic strength you determined in part b). Does the calculation including these activity corrections predict more or less dissolution of fluorite?

d) Repeat the calculations from part a) but this time assuming that the groundwater has an initial ionic strength of 0.01 and an initial concentration of Ca2+ of 0.55 x 10^-3 mol/L. (Note that you will need to use the extended Debye-Huckel equation for activities at this ionic strength. Also, remember that each mole of fluorite that dissolves will add one mole of Ca2+ and two moles of F- to what is already in solution.)


You should use excel for this questions.

Consider a saturated solution of calcium fluoride in 0.092 M potassium nitrate. Complete the following tasks, and then answer the question.a) Write the chemical equation corresponding to Ksp.b) Write the defining expression for the thermodynamic solubility product constant, Kspo.c) Write the defining expression for the conditional solubility product constant, Ksp'.d) For the Ca2+ and F- ions, write the mathematical relations defining activity of each ion in terms of its concentration and activity coefficient.e) Based on your answers above, derive a relationship for Ksp' in terms of Kspo and activity coefficients, and calculate the value of Ksp', given that Kspo = 3.9 x 10-11. (Note: Compute the activity coefficient for each ion using the Debye-Huckel equation. You can disregard the contribution of the dissolved CaF2 to the overall ionic strength. Also disregard the formation of any HF in the equilibrium solution.) Question:Calculate the molar solubility of the calcium fluoride.

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