Question

1. Tooth enamel consists mainly of hydroxyapatite (Ca5(PO4)3(OH). When tin(II)fluoride is added to toothpaste it reacts with the enamel to produce a more decay-resistant material fluoroapatite ( Ca5(PO4)3F. The by-products of this reaction are tin(II)oxide and water. What mass of hydroxyapatite can be converted to fluoroapatite by reaction with 0.115 grams of tin(II)fluoride

Answer 1

Answer: The mass of hydroxyapatite that can be converted is 0.733 grams

Explanation:

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$     .....(1)

Given mass of tin(II)fluoride  = 0.115 g

Molar mass of tin(II)fluoride = 156.7 g/mol

Putting values in equation 1, we get:

$\text{Moles of tin(II)fluoride}=\frac{0.115g}{156.7g/mol}=0.00073mol$

The chemical equation for the reaction of tin(II)fluoride and hydroxyapatite follows:

$SnF_2+2Ca_5(PO_4)_3(OH)\rightarrow 2Ca_5(PO_4)_3F+SnO+H_2O$

By Stoichiometry of the reaction:

1 mole of tin (II) fluoride reacts with 2 moles of hydroxyapatite

So, 0.00073 moles of tin (II) fluoride will react with = $\frac{2}{1}\times 0.00073=0.00146mol$ of hydroxyapatite

Now, calculating the mass of hydroxyapatite by using equation 1, we get:

Moles of hydroxyapatite = 0.00146 moles  

Molar mass of hydroxyapatite = 502.3 g/mol

Putting values in equation 1, we get:

$0.00146mol=\frac{\text{Mass of hydroxyapatite}}{502.3g/mol}\\\\\text{Mass of hydroxyapatite}=(0.00146mol\times 502.3g/mol)=0.733g$

Hence, the mass of hydroxyapatite that can be converted is 0.733 grams