Empirical Formula of Crocetin?

  • Thread starter DavidQT
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Crocetin consists of elements carbon, hydrogen and oxygen. Determine the empirical formula of crocetin, if 1.00g of crocetin forms 2.68g of carbon dioxide and 0.657g of water when it undergoes complete combustion.

I have tried this question several times but I can't get the right answer and I don't know what I am doing wrong. I have asked some classmates and they got the answer to be C5H60.
 

Answers and Replies

  • #2
Borek
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C5H6O looks OK to me. Hard to comment on what you did wrong not seeing what you did.

Please note this should land in homework forums. Moving.
 
  • #3
Wikipedia says crocetin is C20H24O6
Divide it all by four and your answer is correct :)
 
  • #4
Borek
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Wikipedia says crocetin is C20H24O6
Divide it all by four and your answer is correct :)

It either is, or is not. It fits the formula, but we don't know if it fits data they were given (and they will be graded for the latter, not for their ability to google).
 
  • #5
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Still Dont get iit

Ok I have a test tomorrow and I still dont get this question.

Crocetin consists of elements carbon, hydrogen and oxygen. Determine the empirical formula of crocetin, if 1.00g of crocetin forms 2.68g of carbon dioxide and 0.657g of water when it undergoes complete combustion.

This is what i did:
2.68/44.01=0.0609 mols of carbon dioxide. 0.657/18.02=0.0365 mols of water.
0.0609/0.0365=1.67 0.0365/0.0365=1
1.67x3= 5 to get it even for the empirical formula. 1x3=3 Have to multiply by 3 to both.
Empirical formula= (CO2)5 (H20)3=C5H6O13. Im pretty sure the answer is C5H60
 
  • #6
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Dividing by 4 does not work anyways 6 oxygen's divided by 4 does not equal 1 oxygen.
 
  • #7
Borek
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Typo, crocetin doesn't contain 6 oxygen atoms but 4.
 
  • #8
Borek
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2.68/44.01=0.0609 mols of carbon dioxide. 0.657/18.02=0.0365 mols of water.
0.0609/0.0365=1.67 0.0365/0.0365=1
1.67x3= 5 to get it even for the empirical formula. 1x3=3 Have to multiply by 3 to both.
Empirical formula= (CO2)5 (H20)3=C5H6O13. Im pretty sure the answer is C5H60

You are assuming that products of combustion contain the same amount of oxygen as crocetin did. That's obviously impossible - you have 2.68+0.657=3.34 g of products, but there was only 1 g of crocetin. No wonder your oxygen is so off.
 
  • #9
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Then how would I go about fixing my mistake.
 
  • #10
Borek
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Calculate mass of carbon in 2.68g of CO2, calculate mass of hydrogen in 0.657g of H2O, subtract these from the original sample mass - that's the mass of oxygen in the original sample.

Enough spoon feeding for today, now you are on your own.
 
  • #11
Wow, Borek, you are so rude. Not everyone has the privilege of a good education. Or has English as a first language. I had no idea what combustion is, we did not say anything about it in class as it is apparently assumed to be common knowledge. I know it in my language, never had to translate the word into English before. So how was I supposed to know that combustion involves an excess of oxygen? The point is that you should be more considerate as a teacher. If you were to tell me 'enough spoon feeding' in class I would have been not only discouraged from asking you questions in the future, but also like an idiot for even struggling with that question. And I was really struggling, believe me, and it was not because I was too lazy to think, I didn't even realise that combustion involves excess oxygen. Do you feel better about yourself being rude to people?
 

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