# Problem: Tooth enamel consists of hydroxyapatite, Ca 5(PO4)3OH (Ksp = 6.8 × 10−37). Fluoride ion added to drinking water reacts with Ca5(PO4)3OH to form the more tooth decay–resistant fluorapatite, Ca5(PO4)3F (Ksp = 1.0 × 10−60). Fluoridated water has dramatically decreased cavities among children. Calculate the solubility of Ca5(PO4)3OH and of Ca 5(PO4)3F in water.

###### FREE Expert Solution

For Ca5(PO4)3OH: Since the Ca5(PO4)3OH is an ionic compound, it forms ions when dissociating in water. The dissociation of Ca5(PO4)3OH in water is as follows:

Ca5(PO4)3OH(s)  5 Ca2+(aq) + 3 PO43+(aq) +  OH(aq)

We can construct an ICE table for the dissociation of Ca5(PO4)3OH

Remember that solids are ignored in the ICE table and Ksp expression.

93% (432 ratings)
###### Problem Details

Tooth enamel consists of hydroxyapatite, Ca 5(PO4)3OH (Ksp = 6.8 × 10−37). Fluoride ion added to drinking water reacts with Ca5(PO4)3OH to form the more tooth decay–resistant fluorapatite, Ca5(PO4)3F (Ksp = 1.0 × 10−60). Fluoridated water has dramatically decreased cavities among children. Calculate the solubility of Ca5(PO4)3OH and of Ca 5(PO4)3F in water.