Chem Question?

Perovskite is a compound with a cubic unit cell and has a strontium atom at the center of the cell, titanium atoms at the corners of the unit cell, and oxygen atoms at the centers of each edge of the unit cell. If the edge length of the unit cell is 3.905 Å, calculate the density of perovskite in g/cm3.


So, each cell contains one full strontium atom, one full titanium atom (8 eighths), and 3 full oxygen atoms (12 edges with 1/4 atom inside the cell on each edge). The atomic masses of strontium, titanium, and oxygen are 87.6, 47.9, and 16.0. So the mass of a unit cell in amu is 151.5, which translates to 2.516 x 10^(-22) grams. An Angstrom is 10^(-8) cm, so the volume of the unit cell is (3.905 x 10^(-8) cm)^3 = 5.955 x 10^(-23) cm^3. Then the density of the compound is (25.16 gram)/(5.955 cm^3) = 4.2 g/cm^3.