Coordination Compounds 2 Question 23
####25. The recommended concentration of fluoride ion in drinking water is up to $1 ppm$ as fluoride ion is required to make teeth enamel harder by converting $\left[3 Ca _3\left(PO _4\right) _2 \cdot Ca(OH) _2\right]$ to :
(2018 Main)
(a) $\left[CaF _2\right]$
(b) $\left[3\left(CaF _2\right) \cdot Ca(OH) _2\right]$
(c) $\left[3 Ca _3\left(PO _4\right) _2 \cdot CaF _2\right]$
(d) $\left[3{Ca _3\left(PO _4\right) _2 } \cdot CaF _2\right]$
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Answer:
Correct Answer: 25. (d)
Solution:
- Fluoride ions help in making teeth enamel harder by converting $\left[3 Ca _3\left(PO _4\right) _2 \cdot Ca(OH) _2\right]$ i.e. Hydroxy apatite to $\left[3 Ca _3\left(PO _4\right) _2 \cdot CaF _2\right]$ i.e., Fluorapatite (Harder teeth enamel) via following reaction:
$\left[3 Ca _3\left(PO _4\right) _2 \cdot Ca(OH) _2\right]+\underset{\substack{\text { From } \ \text { drinking } \ \text { water }}}{2 F^{-}} \longrightarrow\left[3 Ca _3\left(PO _4\right) _2 \cdot CaF _2\right]+2 OH^{-}$
