12. At 50°C, the solubility of silver chloride, AgCl, is 5.2 x 104g/100 mL. Calc

Question

12. At 50°C, the solubility of silver chloride, AgCl, is 5.2 x 104g/100 mL. Calculate the Kap at this temperature. Answer 1.3 x 10-9 13. If 1.00 g of MgF2 (FW 62.31) is added to 500. mL of pure water, how many grams dissolve? (Ksp 7.4 x 10-9at 19°C) Answer: 0.038 14. The addition of fluoride to many public water systems is done to help fight cavities in a city's population. Given a 500 mL sample of hard water that contains 2.5 × 10-3 M Ca2+ ions, what is the maximum amount of sodium fluoride, in mg, that can be dissolved in the water with no precipitation? (Ksp CaF2]= 5.3 x 10-*) Answer: 30.6 mg

Explanation / Answer

12)

solubility of AgCl = 5.2 x 10^-4 g / 100 mL

                          = 5.2 x 10^-3 g / L

                          = 5.2 x 10^-3 / 143.32

                          = 3.628 x 10^-5 M

AgCl -------------> Ag+   + Cl -

Ksp = [Ag+][Cl-]

     = (3.628 x 10^-5)^2

Ksp = 1.3 x 10^-9

13)

solubility of MgF2 = 1.00 / 0.5 = 2.0 g / L

                           = 0.0321 M

Ksp = 7.4 x 10^-9

Ksp = 4 S^3

7.4 x 10^-9 = 4 S^3

S = 0.00123 M

solubility = 0.00123 x 62.3 = 0.0765

mass of dissolve amount = 0.038 g

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