A certain compound with a molar mass of 120.0 g/mol crystallizes with the sodium chloride (rock salt) structure. The length of an edge of the unit cell is 461 pm. What is the density of this compound

Respuesta :

The density of the compound is 4.64 g/[tex]cm^{3}[/tex].

Explanation:

Sodium chloride crystallize as FCC face centered cubic structure. It consist of four atoms of NaCl. So the unknown compound which crytallizes like NaCl wil have volume as:

radius in fcc is calculated as

[tex]\sqrt{2a}[/tex] = 4r

putting the value where a is length of the edge.

[tex]\sqrt{2X461}[/tex]

= 651.9 = 4r  so r= 162.98 pm

volume is calculated by the formula:

[tex]\frac{4}{3}[/tex] π[tex]r^{3}[/tex]

putting the values,

[tex]\frac{4}{3}[/tex] x 3.14 x ([tex]1.62 X 10^{-8}[/tex])^3

= 4.25X 10 ^-24

1.7 X [tex]10^{-23}[/tex] [tex]cm^{3}[/tex] = volume of the fcc cell.

mass of the substance = 4 x 120 x 1.6605 x 10^(-24) g/u) (as it contains four atoms)

                                     = 7.9x [tex]10^{-23}[/tex]

density = [tex]\frac{mass}{volume}[/tex]

putting the values

density = [tex]\frac{ 7.9x10^-23 }{1.7 x 10^{-23} }[/tex]

density = 4.64 g/ [tex]cm^{3}[/tex]