Tooth enamel is composed of the mineral hydroxyapatite, Ca5(PO4)3(OH), which ionizes water as follows: Ca5(PO4)3(OH)(s) ⇌ 5Ca2+(aq) + 3PO43–(aq) + OH–(aq) (a) Write the expression for Ksp of this compound. (b) If the solubility of hydroxyapatite in water is S mol/L, what is Ksp in term of S? (c) If Ksp= 6.8 x 10–37, calculate the solubility of Ca5(PO4)3(OH) in water in mol/L.
Tooth enamel is composed of the mineral hydroxyapatite, Ca5(PO4)3(OH), which ionizes water as follows:
Ca5(PO4)3(OH)(s) ⇌ 5Ca2+(aq) + 3PO43–(aq) + OH–(aq)
(a) Write the expression for Ksp of this compound.
(b) If the solubility of hydroxyapatite in water is S mol/L, what is Ksp in term of S?
(c) If Ksp= 6.8 x 10–37, calculate the solubility of Ca5(PO4)3(OH) in water in mol/L.
(d) How is the solubility of hydroxyapatite affected by adding acid? Is the solubility in acidic solution higher or lower compared with that in water?
(e) When hydroxyapatite is treated with fluoride, the mineral fluoroapatite, Ca5(PO4)3F, is formed. This mineral has Ksp~ 1 x 10–60. Write equation for the ionization of fluoroapatite in water, the expression for Ksp,and calculate its solubility in water.
(f) Compare the solubility of fluoroapatite, Ca5(PO4)3F, with that of hydroxyapatite, Ca5(PO4)3(OH), and explain the rationale for the fluoridation of drinking water.
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