How do you calculate the density of a body centered unit cell?
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Nikole S asked:
Ok so I keep coming up with a number that I am sure is way too small. 1.0282E-19g/cmcubed
Ok so I keep coming up with a number that I am sure is way too small. 1.0282E-19g/cmcubed
The question is
When molybdenum crystallizes, it forms body-centered cubic cells. The unit cell edge length is 314.1 pm. Calculate the density of molybdenum. (Enter answer to three significant figures.)
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August 15th, 2008 at 7:48 pm
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August 16th, 2008 at 9:17 pm
How many atoms are there in a body centered cubic cell? What do those atoms mass to? Convert this number to grams.
What is the volume of a cube which is 314.1 pm on an edge? Convert to cm³.
Divide mass by volume.
August 18th, 2008 at 10:43 am
The density of the unit cell, ?, is given by:
? = ZM / a³N ;
where Z is the formula units per unit cell, M the molar mass per formula unit, a the cubic unit cell lattice parameter, and N the Avrogadro constant.
For bcc, Z = 2
For molybdenum, M = 95.94 g mol?¹
and a = 314.1 pm = 314.1 x 10?¹² m
Substituting gives, ? = (2)(95.94) / {(314.1×10E-12)³(6.022×10²³)}
= 1.03 x 10E7g m?³
= 10.3 g cm?³
The density of the crystal is 10.3 g cm?³ (to 3 s.f.).