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Topic: Help with finding weight of an unknown sample....  (Read 2791 times)

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Offline Claire_95

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Help with finding weight of an unknown sample....
« on: December 09, 2011, 08:57:11 PM »
Okay, so there are 1.49 moles of Mg(NO3)2. There are 1.229*10E19 atoms of N in an unknown sample of Mg(NO3)2. How many miligrams will the sample weigh? I've tried everything I can think of, and I'm still stuck!
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Offline Arkcon

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Re: Help with finding weight of an unknown sample....
« Reply #1 on: December 09, 2011, 09:08:18 PM »
OK, you have 3 different units in this question:  moles, number of atoms, and grams.  Do you know the relationship between the 3 so you can convert?
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Offline Claire_95

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Re: Help with finding weight of an unknown sample....
« Reply #2 on: December 09, 2011, 09:10:55 PM »
Yes
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Offline Borek

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Re: Help with finding weight of an unknown sample....
« Reply #3 on: December 10, 2011, 02:43:31 AM »
Numbers given (1.49 moles and 1.229x1019) are unrelated - they don't describe the same sample. Ignore 1.49, it is there just to confuse you.
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Offline vmelkon

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Re: Help with finding weight of an unknown sample....
« Reply #4 on: December 10, 2011, 10:18:20 AM »
Sounds like you have 2 samples of Mg(NO3)2, but they are asking for the one with 1.229*10E19 atoms.

Use Avogadro's number to convert # of atoms to moles (because we all like working with small numbers instead of insanely large numbers).

1.229*10E19 atoms / Avogadro = number of moles of Mg(NO3)2

Then convert the # of moles to grams. Find the molar mass of Mg(NO3)2 which a simple search will provide or just calculate it yourself.
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