Chemistry
posted by Luc .
An element has ccp packing with a facecentered cubic unit cell. Its density is 12400 kg/m3 and the unit cell volume is 5.50 x 1029 m3. Calculate the molar mass (g/mol) of the element to three significant figures.
Please explain how you come to the answer.

Well, this is rather a question concerning both, physics as well as chemistry.
You certainly know from physics:
density = mass / volume
Even though your provided information seem to be in a disturbingly unmathematical order, I presume your familiarity with calculating the volume of a cube. Elementary transformation of the aforesaid equations immediately yields:
mass = density * volume
From this and the periodic system of elemnts, you can easily derive the answer. 
#atoms/unit cell x molar mass/Avogadro's number = mass of unit cell.
You have # atoms/unit cell (4) and Avogadro's number. That leaves only molar mass to calculate after mass is determined
Next, mass = volume x density. You have volume and density, that calculates mass. Post your work if you get stuck.