Milk of magnesia contains Mg(OH)_2. At 25degree C, the K_sp for Mg(OH)_2 is 5.6

Question

Milk of magnesia contains Mg(OH)_2. At 25degree C, the K_sp for Mg(OH)_2 is 5.6 times 10^-11. What is the pH of a saturated Mg(OH)_2 solution? 2. The K_sp for AgBr is 5.4 times 10^-13. What is the molar solubility of AgBr in a 0.040 M solution of NaBr? 3. At 25degree C, the molar solubility of Ag_3PO_4 is 4.3 times 10^-5 moles per liter. Calculate the value of K_sp for Ag_3PO_4. 4. What is the molar solubility of Cu(OH)_2 in pure water? What is its molar solubility in a buffer solution with a pH of 10.0? For Cu(OH)_2, the K_sp = 2.5 times 10^-16.

Explanation / Answer

1) Mg(OH)2 ----------------> Mg+2 + 2OH-

S 2S

Ksp = [Mg+2][OH-]^2

5.6 x 10^-11 = (S)(2S)^2 = 4 S^3

S = 2.41 x 10^-4 M

[OH-] = 2S = 4.82 x 10^-4 M

pOH = -log [OH-] = 3.32

pH + pOH = 14

pH = 10.68

2)

AgBr ------------------Ag+ + Br-

S 0.04

Ksp = [Ag+] [Br-]

5.4 x 10^-13 = S x 0.040

S = 1.35 x 10^-11 M

molar solubility = 1.35 x 10^-11 M

3)

S = 4.3 x 10^-5 M

Ag3PO4 ------------> 3Ag+ + PO4-3

3S S

Ksp = (3S)^3(S) = 27 S^4

Ksp = 27 (4.3 x 10^-5)^4

Ksp = 9.23 x 10^-17

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