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Topic: Empirical Formulas  (Read 8796 times)

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DarkMetalDragon

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Empirical Formulas
« on: February 27, 2005, 05:54:19 PM »
If anyone could help me see where I'm messing up, I'd greatly appreciate it. Thank you.

Determine the empirical formula for compouds that have the following analyses:

60.9% As and 31.9% S

I have the answer key for this problem, I just have to show the correct work to get to there. The problem is, I do the problem, but don't come up with the correct answer.

60.9 g As (1 mol) = .813 = 1
              74.92      .813

39.1 g S (1 mol) = 1.220= 2
               32.06     .813

*Note when I used the numbers 1.220 and .833 I didn't round them off there. I punched the full answers in my calculator, but for writing purposes I just wrote them down as .833, etc.

I end up getting as my final answer: AsS2
when the answer should be: As2S3.

If anyone can tell me where I'm off, I'd appreciate it a lot. Thanks.
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Offline Borek

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Re:Empirical Formulas
« Reply #1 on: February 27, 2005, 06:13:48 PM »
Since when 1.220/0 .813 = 2 ?

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DarkMetalDragon

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Re:Empirical Formulas
« Reply #2 on: February 27, 2005, 06:17:01 PM »
If you have something like 1.5 you have to round up to 2.
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Offline Donaldson Tan

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Re:Empirical Formulas
« Reply #3 on: February 27, 2005, 07:47:13 PM »
1.22/.8.13 = 1.5 = 3/2
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DarkMetalDragon

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Re:Empirical Formulas
« Reply #4 on: February 27, 2005, 08:29:33 PM »
Geodome,

How did you get the 3/2? That's what I don't understand.
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savoy7

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Re:Empirical Formulas
« Reply #5 on: February 27, 2005, 10:28:49 PM »
DMD

As Geodome et al. stated you've should have gotten a 1:1.5 ratio.

Since an emperical formula is the simplest whole number ratio, we have to double this ratio to get 2/3.

giving us As2S3

The numbers have to be whole numbers and 1.5 is inbetween, so you just can not just round it up to 2.  

I hope this helps,
savoy
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DarkMetalDragon

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Re:Empirical Formulas
« Reply #6 on: February 27, 2005, 10:54:34 PM »
Savoy,

Thanks for your help. I was thinking about it lots, and then I thought about how you have to double it since you can't round it. You also can't do that stuff if you have .25,.33,.75, etc. Duh, right. Lol.

Thanks for your help. :D
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dexangeles

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Re:Empirical Formulas
« Reply #7 on: February 27, 2005, 11:10:19 PM »
this is the best way to learn :Lighten:
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DarkMetalDragon

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Re:Empirical Formulas
« Reply #8 on: February 27, 2005, 11:35:59 PM »
Yeah, I guess you're right. I'm glad that I have an answer key to check and see if I'm doing this right as I'm going along. Otherwise I would have had like about a good 3/4 of my worksheets done all wrong... uh whoops? ;)

It's amazing what you can find on google when you're trying to type in stuff like empirical formulas. I came across this site while doing so, and now I'm glad I have a place I can ask some questions and get some help. Thanks everyone.
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