Environmental Chemistry

The F- ions make the enamel on teeth much harder by converting hydroxyapatite (the enamel on the surface of teeth) into much harder fluoroapatite having the formula.

1. [3 (Ca3(PO4)2) CaF2]
2. [3 (Ca3(PO4)2) Ca(OH)2]
3. [3 (Ca3(PO4)3) CaF2]
4. [3 (Ca2(PO4)2) Ca(OH)2]

Answer

(1) [3 (Ca3(PO4)2) CaF2]

Solution

Hydroxyapatite (enamel) is [3(Ca3(PO4)2) Ca(OH)2].

F- replaces OH-, which gives fluoroapatite [3(Ca3(PO4)2) CaF2].

(2) is hydroxyapatite itself, and Ca3(PO4)3 in (3) and Ca2(PO4)2 in (4) are not neutral formulae, so they are wrong.

Answer: (1)