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### Topic: Empirical Formulas  (Read 9004 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.

#### 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.

#### 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
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

#### DarkMetalDragon

• Guest
##### 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.

#### 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

#### DarkMetalDragon

• Guest
##### 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.

#### 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:

#### DarkMetalDragon

• Guest
##### 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.