What is the solubility of Mg(OH)2 in an aqueous solution buffered to a pH of 13.
ID: 503859 • Letter: W
Question
What is the solubility of Mg(OH)2 in an aqueous solution buffered to a pH of 13.13? The Ksp of Mg(OH)2 is 1.8 x 10-11. Hint: Determine the [OH-] from the pH then deal with solubility with common ion.
Determine if adding each of the following to a saturated Ca3(PO4)2 solution will increase, decrease, or have little to no effect on it ssolubility.
HCl
CaCl2
NaCl
Na3PO4
increase
Decrease
Little to no effect
- A. B. C.HCl
- A. B. C.CaCl2
- A. B. C.NaCl
- A. B. C.Na3PO4
A.increase
B.Decrease
C.Little to no effect
Explanation / Answer
Solubility of Mg(OH)2 at pH 13.13
pOH = 14 - pH
= 14 - 13.13 = 0.87
pOH = -log[OH-] = 0.87
[OH-] = 0.135 M
Ksp for Mg(OH)2 = 1.8 x 10^-11
solubility = [Mg2+] = Ksp/[OH-]^2
= 1.8 x 10^-11/(0.135)^2
= 9.88 x 10^-10 M
Addition of following on the solubility of Ca3(PO4)2
HCl : A
Added H+ reacts with PO4^3- in solution and reduce its concentration. According to Lechatellier's Principle more of salt would dissolve until concentration is reestablished to equilibrium state.
CaCl2 : B
Decrease and more of Ca2+ in solution would shift equilibrium towards reactant end.
NaCl : C
No effect. NaCl gives neutral pH
Na3PO4 : B
Increase as common ion PO4^3- in solution would force more of salt to form.
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