Stupid Stoichiometry

[ugly_boy]

OK I know this is super basic but I don't know how to do this problem: What is the mass, in grams, of one coppur atom?

I thought that mass in grams was equal to amu, but I got that wrong on the test (I put 63.55 g because that was what I had for amu on my periodic table). What to do?

Comments

[cowbert]

grams/mol is equal to amu. Divide your answer by a mole of copper atoms and you'll have grams per atom.

[ugly_boy]

So 63.55amCu/NACu = grams of Cu in one atom. Thank you!

[cowbert]

well it's 63.55gCu/NA (when I said equal, I meant they were numerically equivalent) but you still have to keep your units correct :).

[anonymous]

Divide the amu by Avogadro's number.

The P. table gives you the molar mass - the weight of one mole of the substance. Avogadro's number gives the number of atoms in a mole.
g/atom = g/mol * mol/atom = (g/mol)* 1/(atom/mol).
So for copper:
63.55 g/mol * 1/(6.022*10^23) mol/atom = 1.06*10^-22 g/atom

(Alternatively, the value of the molar mass is also the mass of one atom in amu. Because of the way amu are defined, you have to divide the value by Avogadro's number to get from amu to grams)

At least that's how I would do it =)