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Author Topic: How do I figure out empirical formulas when I'm given mol of certain atoms?  (Read 1897 times)

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Edgar9760

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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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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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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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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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Fe3O4 it is.
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Edgar9760

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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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What is the definition of a hydrocarbon?
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Edgar9760

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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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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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