Question

The conversion of hydroxyapatite occurs due to presence of \(F^-\) ions in water. The correct formula of hydroxyapatite is :

• A. \([3Ca_3(PO_4)_2 \cdot CaF_2]\)
• B. \([Ca_3(PO_4)_2 \cdot CaF_2]\)
• C. \([3Ca_3(PO_4)_2 \cdot Ca(OH)_2]\)
• D. \([3Ca(OH)_2 \cdot CaF_2]\)

Hint:

Think of "hydroxy" as signifying the presence of hydroxide groups (\(OH^-\)). The conversion to "fluorapatite" is why fluoride is added to toothpaste—it makes teeth stronger!

Answer 1

The Correct Option is C

The question tests your knowledge of chemical formulas, specifically hydroxyapatite, which is a key component in tooth enamel and bones. The hydroxyapatite formula is closely related to the presence of fluoride ions and its conversion.

First, let's analyze the options given:

1. \([3Ca_3(PO_4)_2 \cdot CaF_2]\)
2. \([Ca_3(PO_4)_2 \cdot CaF_2]\)
3. \([3Ca_3(PO_4)_2 \cdot Ca(OH)_2]\) - This is the formula for hydroxyapatite.
4. \([3Ca(OH)_2 \cdot CaF_2]\)

Hydroxyapatite is typically denoted by the formula \([Ca_{10}(PO_4)_6(OH)_2]\) when expanded, which simplifies to \([3Ca_3(PO_4)_2 \cdot Ca(OH)_2]\) for practical purposes. The presence of hydroxyl groups (\(OH^-\)) instead of fluoride suggests that option 3 directly correlates with hydroxyapatite.

Let's break down why the other options are incorrect:

• Option 1 and 2 involve \([CaF_2]\), which refers to the fluoride version of fluoride-modified hydroxyapatite, also known as fluorapatite, not pure hydroxyapatite.
• Option 4 suggests only calcium hydroxide and fluoride, which does not comprise hydroxyapatite or its theoretical counterpart.

Therefore, the correct answer is \([3Ca_3(PO_4)_2 \cdot Ca(OH)_2]\), indicating the presence of calcium, phosphate, and hydroxyl ions, representing hydroxyapatite.