Question #fa394

1 Answer
Feb 28, 2017

Answer:

#"In one mole of ferric oxide?"#

Explanation:

A #"mole"# specifies a quantity of #6.022xx10^23# individual items of stuff. We use it in the same way as we would use a #"dozen"#, or a #"bakers' dozen"#, or a #"gross"#. It is simply another (admittedly large) collective number.

We have #1*mol #, #6.022xx10^23# formula units of #Fe_2O_3#, i.e. #2xxN_A# #"iron atoms"#, and #3xxN_A# #"oxygen atoms"#, where #N_A-=6.022xx10^23*mol^-1#. And thus, there are #2xx6.022xx10^23# iron atoms in such a molar quantity.

Now I know #N_A# iron atoms have a mass of #55.8*g#, and #N_A# oxygen atoms have a mass of #15.999*g#. How do I know this?

And thus #1*mol# of #"ferric oxide"# has a mass of #1*molxx(2xx55.8*g*mol^-1+3xx16.00*g*mol^-1)=159.60*g#.

Do you agree?