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Topic: Determining molecular formula of a compound  (Read 3024 times)

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Offline aerosam

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Determining molecular formula of a compound
« on: May 12, 2012, 07:48:43 PM »
Hi

Suppose i have an unknown inorganic compound, is there a way to determine it's molecular composition.
For example could a mass spectrometer be used? If not which other device should i use? How would the presence of small amounts of impurities affect the results?

Thanks
Sam


Offline gelminil

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Re: Determining molecular formula of a compound
« Reply #1 on: May 15, 2012, 04:44:06 PM »
I suppose a mass spectrometer could be used.
usually you can do this gravimetrically.

If you know it has Ba2+ and Cl- ions.
You can precipitate the Ba2+ with sulphate ions and the cl- with silver nitrate.  Compare the moles of each.



Offline discodermolide

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Re: Determining molecular formula of a compound
« Reply #2 on: May 21, 2012, 05:47:39 AM »
Hi

Suppose i have an unknown inorganic compound, is there a way to determine it's molecular composition.
For example could a mass spectrometer be used? If not which other device should i use? How would the presence of small amounts of impurities affect the results?

Thanks
Sam



A MS will only give you the molecular weight of the compound plus the weight of fragment ions. I suppose you could piece it together but you will probably get the wrong answer. Impurities will make the MS harder to interpret-
The best way is elemental analysis. Here impurities will significantly affect the results.
NMR and IR will help a lot in this respect, the former will tell you what functionality is present, the latter what functional groups are in the molecule.


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Offline discodermolide

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Re: Determining molecular formula of a compound
« Reply #3 on: May 28, 2012, 06:24:03 PM »
Hi

Suppose i have an unknown inorganic compound, is there a way to determine it's molecular composition.
For example could a mass spectrometer be used? If not which other device should i use? How would the presence of small amounts of impurities affect the results?

Thanks
Sam



A MS will only give you the molecular weight of the compound plus the weight of fragment ions. I suppose you could piece it together but you will probably get the wrong answer. Impurities will make the MS harder to interpret-
The best way is elemental analysis. Here impurities will significantly affect the results.
NMR and IR will help a lot in this respect, the former will tell you what functionality is present, the latter what functional groups are in the molecule.




Please ignore my comment concerning NMR and IR, I read organic for inorganic, apologies.
Development Chemists do it on Scale, Research Chemists just do it!
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