Respuesta :
In a sample of pure calcium fluoride of mass 15.0 g, 7.70 g of calcium is present. First convert the mass into number of moles as follows:
[tex]n=\frac{m}{M}[/tex]
Here, m is mass and M is molar mass.
Molar mass of Ca is 40 g/mol, putting the values,
[tex]n=\frac{7.70 g}{40 g/mol}=0.1925 mol[/tex]
Similarly, molar mass of [tex]CaF_{2}[/tex] is 78.07 g/mol thus, number of moles will be:
[tex]n=\frac{15.0 g}{78.07 g/mol}=0.1921 mol[/tex].
Thus, 0.1921 mol of [tex]CaF_{2}[/tex] have 0.1925 mol of Ca, or 1 mole of [tex]CaF_{2}[/tex] will have approximately 1 mole of Ca.
Now, mass of Ca needs to be calculated in 45.0 g of [tex]CaF_{2}[/tex]. Converting mass into number of moles first,
[tex]n=\frac{45.0 g}{78.07 g/mol}=0.5764 mol[/tex]
Thus, number of moles of Ca will also be 0.5764 mol, converting number of moles into mass,
[tex]m=n\times M=0.5764 mol\times 40 g/mol=23.06 g[/tex]
Therefore, mass of Ca will be 23.06 g.
