Question
An element has ccp packing with face-centered cubic unit cell. Its density is 3.78 g/cm^3 and the unit cell volume is 2.31 x 10^-25 L. Calculate the molar mass (g/mol) of the element to 3 sig figs.
the answer is 131 g/mol
i first changed 2.31 x 10^-25 L to 2.31 x 10^-22 mL and multiplied that by 3.78 g/mL
after that i got m = 8.73 x 10^-22 g
& multiplied that by 6.022 x 10^23 = 525.7
and the only way i get 131 g/mol is when i divide 525.7/4....my question is WHY DO YOU DIVIDE BY 4????
pleasee help thank youu :)
the answer is 131 g/mol
i first changed 2.31 x 10^-25 L to 2.31 x 10^-22 mL and multiplied that by 3.78 g/mL
after that i got m = 8.73 x 10^-22 g
& multiplied that by 6.022 x 10^23 = 525.7
and the only way i get 131 g/mol is when i divide 525.7/4....my question is WHY DO YOU DIVIDE BY 4????
pleasee help thank youu :)
Answers
You did it correctly. The four (4) comes from the fact that there are four atoms to the unit cell; therefore, 4*mass of 1 atom = mass of the unit cell.