8) Ksp for Ca5(PO4)3OH = [Ca2+]^5.[PO4^3-]^3.[OH-] pH = 7 [OH-] = 1 x 10^-7 M so

Question

8) Ksp for Ca5(PO4)3OH = [Ca2+]^5.[PO4^3-]^3.[OH-]

pH = 7

[OH-] = 1 x 10^-7 M

solubility = 5.5 x 10^-5 M

So,

Ksp = (5 x 5.5 x 10^-5)^5.(3 x 5.5 x 10^-5)^3.(1.0 x 10^-7)

       = 7.07 x 10^-37

When pH = 3

pOH = 14 - pH = 11

[OH-] = 1 x 10^-11 M

let solubility be x,

Ksp = (5x)^5.(3x)^3.(1 x 10^-11)

4 x 10^-34 = (125 x 27)(x^8)(1 x 10^-11)

x = 1.9 x 10^-4 M

So the solubility at pH 3 would be,

d) 1.7 x 10^-4 mol/L

9) For [HF] = 0.15 M

pKa = -logKa

Ka = 6.8 x 10^-4

acid dissociation,

HF + H2O <==> H3O+ + F-

let x amount has dissociated

Ka = [H3O+][F-]/[HF]

6.8 x 10^-4 = x^2/(0.15 - x)

x^2 + 6.8 x 10^-4x - 1.02 x 10^-4 = 0

x = 9.765 x 10^-3 M

Percent dissociation = (x/[HF]) x 100

                                 = 1.02 x 10^-3 x 100/0.15 = 6.5%

Answer,

b) 6.5%

Explanation / Answer

Please answer both questions asap I will gladly rate

th enamel is composed of hydroxyapatite, Cas(POs) OH, but toothpaste ads warn against "acid erosion" due to acidic foods and beverages. If the solubility of Cas(PO4) sOH in water (buffered at pH 7) is 5.5 x 10 mol/L, what is its solubility in acid (buffered at pH 3)1 a) 1.7 x 1012mol/L b) 2.3 x 10Smol/L c) 4.7 x 10 mol/L d) 1.7 x 10- molVL e) 8.2 x 10 mo/L 9) Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. It is a precursor to almost all fluorine compounds, including pharmaceuticals such asfl and elemental fluorine itself. Because of its high reactivity toward glass and moderate reactivity toward many metals, hydrofluoric acid is usually stored in plastic. Aqueous hydrofluoric acid is a contact-poison potential for deep, initially painless burns and ensuing tissue death percent dissociation of 0.15M HF(aq)? uoxetine (Prozac), diverse materials such as PTFE (Teflon), . If HF has a pKa value of 3.17, what is the a) 0.29% b) 6.5% c) 16% d) 34% e) 65%

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