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 solve this problem, we need to identify the chemical formula of fluoroapatite, which is formed when fluoride ions (F^-) convert hydroxyapatite into a harder substance. The chemical reaction replaces the hydroxyl (OH)^- groups in hydroxyapatite with fluoride ions to form fluoroapatite.

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

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

When fluoride ions are introduced, they replace the hydroxide ions, creating fluoroapatite:

\(Ca_5(PO_4)_3F\)

However, the formula for fluoroapatite often considered in bulk compositions is:

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

Let's evaluate the given options to find the correct formula for fluoroapatite:

1. \([3(Ca_3(PO_4)_2).CaF_2]\) - This formula represents fluoroapatite, where \(3(Ca_3(PO_4)_2)\) combines with \(CaF_2\).
2. \([3(Ca_2(PO_4)_2).Ca(OH)_2]\) - This represents a variant of hydroxyapatite, not fluoroapatite, due to the presence of \((OH)_2\).
3. \([3(Ca_3(PO_4)_3.CaF_2]\) - This formula is incorrectly structured with mismatched brackets.
4. \([3(Ca_3(PO_4)_2.Ca(OH)_2]\) - This is another variant of hydroxyapatite, due to the presence of \((OH)_2\).

After analyzing the options, the correct formula for fluoroapatite is:

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

Hence, the correct answer is the first option.

Answer 2

Explanation:

- Hydroxyapatite, [Ca₅(PO₄)₃(OH)], is present in tooth enamel.

- When fluoride ions (F⁻) are introduced, they replace the hydroxide ions (OH⁻), forming fluoroapatite:

Ca₅(PO₄)₃(OH) + F⁻ → Ca₅(PO₄)₃F.

- Fluoroapatite has the molecular formula [3(Ca₃(PO₄)₂·CaF₂)], which is harder and more resistant to decay.

Final Answer: Option (1).