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Empirical Formula of Crocetin?

  1. Nov 15, 2013 #1
    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.
     
  2. jcsd
  3. Nov 16, 2013 #2

    Borek

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    Staff: Mentor

    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.
     
  4. Nov 23, 2013 #3
    Wikipedia says crocetin is C20H24O6
    Divide it all by four and your answer is correct :)
     
  5. Nov 24, 2013 #4

    Borek

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    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).
     
  6. Nov 24, 2013 #5
    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
     
  7. Nov 24, 2013 #6
    Dividing by 4 does not work anyways 6 oxygen's divided by 4 does not equal 1 oxygen.
     
  8. Nov 25, 2013 #7

    Borek

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    Typo, crocetin doesn't contain 6 oxygen atoms but 4.
     
  9. Nov 25, 2013 #8

    Borek

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    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.
     
  10. Nov 25, 2013 #9
    Then how would I go about fixing my mistake.
     
  11. Nov 25, 2013 #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.
     
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