Question

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:

• A. [3(Ca$_3$(PO$_4$)$_2$).CaF$_2$]
• B. [3(Ca$_2$(PO$_4$)$_2$).Ca(OH)$_2$]
• C. [3(Ca$_3$(PO$_4$)$_3$.CaF$_2$]
• D. [3(Ca$_3$(PO$_4$)$_2$.Ca(OH)$_2$]

Answer 1

The Correct Option is A

To address this, we must identify the chemical formula of fluoroapatite. Fluoroapatite is a harder substance formed when fluoride ions (F^-) substitute for hydroxyl ions in hydroxyapatite. The chemical process involves the exchange of hydroxyl (OH)^- groups within hydroxyapatite for fluoride ions, resulting in fluoroapatite.

Hydroxyapatite, the primary mineral component of tooth enamel, has the following formula:

\(Ca_5(PO_4)_3(OH)\)

Upon the introduction of fluoride ions, they displace the hydroxide ions, forming fluoroapatite:

\(Ca_5(PO_4)_3F\)

However, for bulk compositions, the commonly cited formula for fluoroapatite is:

\(3Ca_3(PO_4)_2.CaF_2\)

We will now evaluate the provided options to determine the correct formula for fluoroapatite:

1. \([3(Ca_3(PO_4)_2).CaF_2]\) - This formula accurately represents fluoroapatite, illustrating the combination of \(3(Ca_3(PO_4)_2)\) with \(CaF_2\).
2. \([3(Ca_2(PO_4)_2).Ca(OH)_2]\) - The presence of \((OH)_2\) indicates this formula represents a form of hydroxyapatite, not fluoroapatite.
3. \([3(Ca_3(PO_4)_3.CaF_2]\) - This formula is structurally incorrect due to mismatched brackets.
4. \([3(Ca_3(PO_4)_2.Ca(OH)_2]\) - This is another representation of hydroxyapatite, identified by the presence of \((OH)_2\).

Following an analysis of the options, the correct formula for fluoroapatite is identified as:

\([3(Ca_3(PO_4)_2).CaF_2]\)

Therefore, the correct selection is the first option.