Intro Chemistry
posted by echem on .
An 0.6600 mol sample of an ionic compound has a mass of 131.9 g. Determine the mass (g) of one formula unit of the compound.
I have no idea how to do the problem. I need help please, I'm reviewing for an exam. Thank You!

moles = grams/formula unit mass
0.660 = 131.9 g/formula unit mass
solve for formula unit mass 
131.9 g * (0.66mol)/(6.022*10^23) =1.4455*10^(22)formula unit I don't think that's right....

I don't think it is either. Where did you get 6.02 x 10^23 and why use it at all?
I gave you the formula.
0.660 = 131.9/formula unit mass.
formula unit mass = 131.9/0.660. Now divide that and see what you get. 
I get 199.848 but I'm pretty sure its suppose to be a small number...
Here's a similar problem that I have the answer to but I don't know how to do...
An 0.4200 mol sample of a metal has a mass of 9.656 g. Determine the mass (g) of one atom of the element. Express answer in scientific notation.
Ans:3.818x10^(23) grams
I think if I know how to get this answer I can get the answer to the other one 
oh i got it!!
(9.656/0.4200)/(6.022E23)= 3.810E23
so I do the same thing for the other problem!
Thank you for you help :) 
199.8 = formula mass is correct, at least from the date you posted. For the other problem.
moles = g/molar mass.
0.420 = 9.656/molar mass.
molar mass = 9.656/0.420 = 22.99.
So far that's the same problem we just solved. For the mass of 1 atom you take 22.99 and divide by 6.022 x 10^23 = 3.818 x 10^23 grams. 
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