# Homework Help: Calculating Molar Mass from a BCC

1. Feb 2, 2009

### vipertongn

1. The problem statement, all variables and given/known data

An element has bcc packing with a body-centered cubic unit cell. Its density is 862 kg/m^3 and the unit cell volume is 1.51 x 10-28 m^3. Calculate the molar mass (g/mol) of the element to three significant figures.

2. Relevant equations

Known: D= 862 kg/m^3, V=1.51 x 10-28 m^3 , MM=??

3. The attempt at a solution

Ok the correct answer is 39.2, but I don't know how to arrive to that answer.

(862kg/m^3)(1.51e-28m^3)(1000g/1kg)(6.022e23atoms/1mol)(1/2 atoms)
(0.68) but instead I get 26.6504.

The 0.68 is the density packing.

2. Feb 2, 2009

### Staff: Mentor

Are you sure it is relevant to the question?

3. Feb 2, 2009

### vipertongn

ah, htat wasn't required, thanks

4. Feb 3, 2009

### Staff: Mentor

The real question is: do you understand what you did and why?

5. Feb 3, 2009

### vipertongn

Yes, I pretty much converted to the proper units I needed, the only problem was getting the right units.

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