Question

The recommended concentration of fluoride ions in drinking water is up to 1 ppm as fluoride ion is by converting $\left[ {3C{a_3}{{\left( {P{O_4}} \right)}_2}.Ca{{\left( {OH} \right)}_2}} \right]$ to:
A.$\left[ {3C{a_3}{{\left( {P{O_4}} \right)}_2}.Ca{F_2}} \right]$
B.$\left[ {3Ca{{\left( {OH} \right)}_2}.Ca{F_2}} \right]$
C.$Ca{F_2}$
D.$\left[ {3\left( {Ca{F_2}} \right).Ca{{\left( {OH} \right)}_2}} \right]$

Answer 1

Hint: The concentration of different cations and anions have different set values as per the BIS standards and different complexing agents and precipitating agents are used to separate out excess concentrations.

Complete step by step solution:
Excess of fluoride ions found in groundwater used for drinking purposes are very hazardous for all the calcium containing organs in our bodies such as the bones, teeth, and blood. This is because the calcium present in these organs are leached out by the fluoride ions to form calcium fluoride, hence the BIS has set the allowable value of fluoride ions in drinking water to 1 ppm.
In the above question, the fluoride ions in the drinking water replace the hydroxyl ions in the above mineral and replace them with fluoride ions by the following reaction:
$\left[ {3C{a_3}{{\left( {P{O_4}} \right)}_2}.Ca{{\left( {OH} \right)}_2}} \right] + 2{F^ - } \to \left[ {3C{a_3}{{\left( {P{O_4}} \right)}_2}.Ca{F_2}} \right] + 2O{H^ - }$

Hence, the correct answer in option (A).

Note: When on one hand excess fluoride is hazardous to our bone, it is also very crucial for the growth and development of our bones and teeth. Fluorine in very small amounts has the ability to resist dental decay and it also helps to resist the demineralization of the bones by accelerating the remineralisation of the minerals back into the tooth enamel. It also has the ability to reduce acid production by interfering with the activities of the acid-producing bacteria and thus inhibit the growth of bacteria.