# Calculate molar mass of a compound from a given molecular mass

The mass of one molecule of a compound is $2.19\times10^{-22}\ \mathrm g$. What is the molar mass of the compound?

My attempt: Using the formula moles=mass/molar mass, I found how to calculate molar mass using the formula molar mass=moles/mass. Therefore, I was under the impression that, surely, $6.02\times10^{23}$ divided by the mass of the compound would have resulted in the molar mass. However, the answer was wrong.

• You know how many molecules of anything are in one mole of that particular anything, so start from there. Aug 20, 2015 at 12:29
• @ToddMinehardt Well I know that I have to divide the amount of moles of this compound over its mass to get to the molar mass. I have tried to get the number of moles through two different but haven't been able to because the compound hasn't been specified , but came to the wrong result twice.
– Tim
Aug 20, 2015 at 12:52
• You might want to include the steps you took towards solving this problem in your post. There is a homework policy for this site which states (in part) that a good-faith effort has to be made by the OP in order to keep the question open. I answered your query based on the effort you detailed in the comment (above). Aug 20, 2015 at 13:57
• Okay, I'll do that now.
– Tim
Aug 20, 2015 at 14:30

To get the molar mass of your mystery compound, make use of the fact that there are $N_{\rm A}$ (Avogadro's number) of molecules of it in one mole of it.
$${\rm molar \;mass} = N_{\rm A}\times 2.19\times 10^{-22}\,{\rm g} = (6.022\times 10^{23}\,{\rm mol}^{-1}) \times (2.19\times 10^{-22}\,{\rm g}) = 131.88\;{{\rm g}\over{\rm mol}}$$