[Sodium-Potassium Pump]

At a certain temperature and pressure an element has the simple body-centred cubic unit cell, depicted below. The corresponding atomic radius is 1.241 Å and the density is 7.875 g cm-3. Calculate (and enter) the atomic mass for this element (in amu).

What I've done:
D = M/V
V = cm³

For body-centered cubic cell l = 4r / sqrt(3)

l = 4(1.241 Å) / 1.732050808
l = 2.86596 Å
V = (2.86596 Å)³
V = 23.540578 ų x (1x10^-24 cm³ / 1 ų
V = 2.3540378x10^-23 cm³

Mass = D x V
Mass = 7.875 g/cm³ x 2.3540378x10^-23 cm³
Mass = 1.85380479x10^-22 g x (1 amu / 1.66053886 x 10^-24 g
Mass = 111.6 amu (with sig figs)

I have submitted this answer and it told me I was incorrect and I have 2 tries left.  What have I done wrong?  Thanks for any *delete me*

[Borek]

For body-centered cubic cell l = 4r / sqrt(3)

sqrt(3) or sqrt(2)?

[Sodium-Potassium Pump]

That's what I wrote down in class but I will try it the other way.

[Borek]

Looks to me like that's a trivial gemoetry - 4r is a hypotenuse of a isosceles right triangle. 2l² = 4r

[Sodium-Potassium Pump]

Got it wrong and now I'm out of chances.  Stupid thing won't even give me the correct answer.

[AWK]

At a certain temperature and pressure an element has the simple body-centred cubic unit cell, depicted below. The corresponding atomic radius is 1.241 Å and the density is 7.875 g cm-3. Calculate (and enter) the atomic mass for this element (in amu).

What I've done:
D = M/V
V = cm³

For body-centered cubic cell l = 4r / sqrt(3)

l = 4(1.241 Å) / 1.732050808
l = 2.86596 Å
V = (2.86596 Å)³
V = 23.540578 ų x (1x10^-24 cm³ / 1 ų
V = 2.3540378x10^-23 cm³

Mass = D x V
Mass = 7.875 g/cm³ x 2.3540378x10^-23 cm³
Mass = 1.85380479x10^-22 g x (1 amu / 1.66053886 x 10^-24 g
Mass = 111.6 amu (with sig figs)

I have submitted this answer and it told me I was incorrect and I have 2 tries left.  What have I done wrong?  Thanks for any *delete me*

Body centered cubic cell has 2 atoms per unit cell!