# Homework Help: Calculating Avagodro's Number

1. Feb 2, 2009

### vipertongn

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

The element Ru has hcp packing with a hexagonal unit cell. The density of Ru is 12410 kg/m^3 and the cell volume is 2.711 x 10-23 mL. Calculate the value of Avogadro's number to three significant figures based on these data. (Note: the value may differ from the tabular value).

2. Relevant equations

D= 12410 kg/m^3 , V= 2.711 x 10-23 mL

3. The attempt at a solution

6 atoms (m^3/12410 kg)(1/2.711e-23 mL)(1000 mL/1 L)(1 L/0.001 m^3)(1 kg/1000g)(101.07 g/1 mol)

I end up with 1.80e24 which is 3x the true value...this method works for every other structure but the hcp

2. Feb 3, 2009

### Staff: Mentor

Are you sure it is six atoms per unit cell?

3. Feb 3, 2009

### vipertongn

I was told that for the base its 2 for simple its 1 and for face its 4, but hcp no one told me except for a tutor and he said it was 6. Is it wrong?

4. Feb 3, 2009

### Staff: Mentor

http://www.chem.ox.ac.uk/icl/heyes/structure_of_solids/lecture1/Lec1.html [Broken]

Last edited by a moderator: May 4, 2017