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#### Edgar9760

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##### How do I figure out empirical formulas when I'm given mol of certain atoms?
« on: October 09, 2011, 10:32:15 PM »

The problem given is:
Determine the empirical formulas of the following compounds:
(a) 0.039 mol of iron atoms combined with 0.052 mol of oxygen atoms

(b) 0.903 g of phosphorous combined with 6.99 g of bromine

(c) A hydrocarbon with 79.9 mass % carbon

I don't know where to start.
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#### Edgar9760

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##### Re: How do I figure out empirical formulas when I'm given mol of certain atoms?
« Reply #1 on: October 09, 2011, 10:43:36 PM »

I started (a) and all I could think of was converting the moles given moles to grams getting the following:
2.18g of iron and 0.832g of oxygen.
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#### Borek

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##### Re: How do I figure out empirical formulas when I'm given mol of certain atoms?
« Reply #2 on: October 09, 2011, 10:55:02 PM »

So you already went in the wrong direction. Empirical formula is about ratio of number of atoms in the molecule - that is much closer to moles than to masses.
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#### Edgar9760

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##### Re: How do I figure out empirical formulas when I'm given mol of certain atoms?
« Reply #3 on: October 09, 2011, 11:01:52 PM »

Ok I tried once more and the answer I got was Fe3O4. The numbers being subscripts. Is that correct?
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#### Borek

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##### Re: How do I figure out empirical formulas when I'm given mol of certain atoms?
« Reply #4 on: October 10, 2011, 12:02:04 AM »

Fe3O4 it is.
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#### Edgar9760

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##### Re: How do I figure out empirical formulas when I'm given mol of certain atoms?
« Reply #5 on: October 10, 2011, 02:07:06 AM »

Thank you. As for part (c), I'm not sure which hydrocarbon the problem is referring to. How do I find that out?
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#### fledarmus

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##### Re: How do I figure out empirical formulas when I'm given mol of certain atoms?
« Reply #6 on: October 10, 2011, 02:29:33 AM »

What is the definition of a hydrocarbon?
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#### Edgar9760

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##### Re: How do I figure out empirical formulas when I'm given mol of certain atoms?
« Reply #7 on: October 10, 2011, 12:41:58 PM »

A compound of hydrogen and carbon, such as any of those that are the chief components of petroleum and natural gas.
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#### fledarmus

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##### Re: How do I figure out empirical formulas when I'm given mol of certain atoms?
« Reply #8 on: October 10, 2011, 03:16:34 PM »

Good - and if it contains only hydrogen and carbon, and it is 79.9% carbon, what would the molecular formula be?
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