Question

ne idea for hydrogen storage is to take advantage of the formation of metallic hydrides. For example, hydrogen is very soluble in metallic palladium. Pd has a FCC lattice in which hydrogen atoms occupy octahedral holes. If 70% of the holes are filled by hydrogen atoms and the lattice does not expand upon hydrogenation, how many grams of hydrogen will be contained in one cubic centimeter of the palladium hydride? The density of Pd is 12.02 g/cm³.

Answer 1

Palladium forms an FCC lattice so there are 4 Pd atoms(6 sides sharing one atom with adjacent unit cell 6x1/2=3 and 8 corners sharing one atom with eight neighboring unit cells 8 x /18 =1, 3+1=4) in the FCC unit cell and for every palladium atom there is one possible octahedral hole. Hydrogen fills 70% of these holes. Mass of Hydrogen with in one unit cell is

= no. of hydrogen atoms x amount of hydrogen filling the holes x mass of hydrogen

= 4 x 0.7 x 1.008 g/mol = 2.8224 g/mol

But 1 mol =6.022 x 10²³ atoms

Mass of hydrogen = 2.8224 x (1/6.022 x 10²³)

= 4.686 x 10^-24 g