Question

3. Tooth enamel consists of the mineral hydroxyapatite, Cas(PO4)3OH, which has Ksp = 6.8 x 10-37. a. (10 points) Fill the in the ICE Box for the equilibrium of hydroxyapatite in water. You may use "x" or "S" for the changes. Cas(PO4)2OH(s) = 5 Ca2+ (aq) + 3 PO43- (aq) + OH- (aq) Initial Change Equilibrium b. (10 points) Write an expression for Ksp in terms of the concentrations of product. C. (10 points) Calculate the solubility of hydroxyapatite in water. Report your answer in mol/L. d. (10 points) Fluoride, when added to drinking water or toothpaste, reacts with Cas(PO4)30H to form the tooth-decay resistant fluoroapetite, reacts with Cas(PO4)3F (Kp = 1.0 x 10-60). Explain how fluoride protects teeth against acidic substances such as coffee and compounds produced by bacteria.

Answer 1

d. The bacteria, acid, food debris, and saliva combine to form plaque, which clings to the teeth. The acids in plaque dissolve the enamel surface of the teeth, creating holes in the teeth called cavities. This is called demineralization of teeth .The formation of small cavities, can be reversed by remineralization--that is, the deposition of minerals into previously damaged areas of tooth. Topical fluoride, when applied frequently in low concentrations, increases both the rate of growth and the size of enamel crystals. The accelerated growth of enamel crystals within the demineralized lesion initiates reminerization of the tooth.

Assume the Cas (PO4), OH we have lM Hydrony apatite. - 5 cat? (aq) + 3 Pozleght or (aq) @ Initial a Change -x - +5x +52 +3x ta Equilibrium 1-X 58 32 from the reaction given we could see that i mole of hydroxyapatite is giving 5 moles of catz ions 3 moles of Posions and Imole of onion hence when & moles of hydrony apatite is dissolved in watu we get 5x moles cations, ax moles of phosphate ions, a moles of Hydroxide ions. (b) © Mx Ny a mnt + ynom kop is given by - ksp = [ant]*[um-] 9 where [Minty is the molar conceno -tration cas (PQ),(OH) Z 5 Catz + 3 PO + OH- Ksp = [cate] [Pd] [ok] Ksp = [cat] [ Pot ] [OH-] det a be the solubility of hydroxyapatite we know the concentration of cats, P03,04 ions when a moles of hydroxyapatite au dissolved (refer act of part a of question) Substituting value of Ksp and molas concentration in the equation Ksp = (5x)} (3x3)(a) = 8437579 Ksp = 8437529 -7X 65X1637, ya 84375 Substitute tsp value. } Ksp = e.sx 10 st given [x = 2.74105 m) Scanned with CamScanner