Question

Spinel is a mineral that contains 37.9% Al, 17.1% Mg, and 45.0% O by mass, and has a density of 3.57g cm-3 . The unit cell is cubic with an edge length of 809 pm (This is a lot bigger than question #2 and #4 for a reason. Think about this after you have calculated an answer). How many atoms of each type are in the unit cell?

Answer #1

The edge length of unit cell

The volume of unit cell

Density of unit cell is 3.57 g/cm3

Mass of unit cell

The percent composition is 37.9 % Al, 17.1 % Mg and 45.0 % O.

Mass of Al in the unit cell

Mass of Mg in the unit cell

Mass of O in the unit cell

The atomic masses of Al, Mg and O are 27 g/mol, 243 g/mol and 16 g/mol respectiely.

Number of Al atoms in unit cell

Number of Mg atoms in unit cell

Number of O atoms in unit cell

This is a lot bigger than question #2 and #4. This is because one unit cell of edge length 809 pm contains several small unit cells having smaller edge length.

Metallic iron crystallizes in a type of cubic unit cell. The
unit cell edge length is 287 pm. The density of iron is 7.87
g/cm^3. How many iron atoms are there within one unit cell?

Copper crystallizes with a face-centered cubic lattice and has a
density of 8.93 g/cm3.
a.) Calculate the mass of one unit cell of copper (in grams) b.)
Calculate the volume of the copper unit cell (in cm3). c.)
Calculate the edge length of the unit cell (in cm). d.) Calculate
the radius of a copper atom (in pm).

Iridium metal crystalizes in a face-centered cubic structure.
The edge length of the unit cell was found by x-ray diffraction to
be 383.9 pm. The density of iridium is 22.42g/cm^3. Calculate the
mass of an iridium atom. Use Avogadro's number to calculate the
atomic mass of iridium.

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