# Chemistry

Iron crystallizes in a body–centered cubic structure. The volume of one Fe atom is 9.38 x 10–24 cm3, and the density of Fe is 7.874 g/cm3. Find an approximate value for Avogadro’s number.

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1. mass of Fe atom = 56 grams/mol

how many cm^3/mol ?

56 g / 7.874 g/cm^3 = 7.11 cm^3/mol

how many atoms is that?

7.11 cm^3/mol / (9.38*10^-24 cm^3/atom)
= .76*10^24 atoms/mol

= 7.6 *10^23

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posted by Damon
2. Damon's method looks MUCH simpler than what I would do but here is mine.
volume Fe atom = 9.38E-24 cc.
V = (4/3)*pi*r^3 and solve for r = radius
For a body centered cubic, a = edge length. 4r = a(3)^1/2 and solve for a.

volume of unit cell = a^3 = about 2.77E-23 cc.

mass unit cell = volume x density = 2.77E-23 x 7.874 = 2.18E-22

u.c. = unit cell
mass u.c. = 2.18E-22 atoms/unit cell x 55.85/N and solve for N.
That's about 5.1E23 compared to the accepted value of 6.02E23.

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posted by DrBob222

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