The well known mineral fluorite is chemically calcium fluoride. It is known that in one unit cell of this mineral there are 4 Ca^(2+) ions and 8F^(-) ions and that Ca^(2+) ions are arranged in a fcc-lattice. The F^(-) ions fill all the tetrahedral holes in the face centred cubic lattice of Ca^(2+) ions. The edge of the unit cell is 5.46 xx 10^(-8) cm in length. The density of the solid is 3.18 g cm^(-3). Use this information to calculate Avogadro's number. (Molar mass of CaF_(2) = 78.08 g mol^(-1))

The well known mineral fluorite is chemically calcium fluoride. It is

1.	The well known mineral fluorite is chemically calcium fluoride. It is known that in one unit cell of this mineral there are 4 Ca^(2+) ions and 8F^(-) ions and that Ca^(2+) ions are arranged in a fcc-lattice. The F^(-) ions fill all the tetrahedral holes in the face centred cubic lattice of Ca^(2+) ions. The edge of the unit cell is 5.46 xx 10^(-8) cm in length. The density of the solid is 3.18 g cm^(-3). Use this information to calculate Avogadro's number. (Molar mass of CaF_(2) = 78.08 g mol^(-1))
Answer» Solution :`d = (Z xx M)/(a^(3) xx N_(A))` For fcc LATTICE Z = 4 3.18 g `CM^(-3) = (4 xx 78.08 g mol^(-1))/((5.46 xx 10^(-8)cm)^(3) xx N_(A))` `N_(A) = (4 xx 78.08 g mol^(-1))/((5.46 xx 10^(-8)cm)^(3) xx 3.18 g cm^(-3))` `N_(A) = 6.033 xx 10^(23) mol^(-1)`