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What's the correct answer here? (petroleum cracking)

  1. Nov 6, 2016 #1
    • Poster has been reminded to post all schoolwork-type questions in the HH forums
    image.jpg image.jpg This is not a homework so don't throw this to the homework area
    This is a dispute between two teachers
    Here is the question and the teacher says D is the correct answer
    But I found a ppt online with the same question with a different answer
    Please help and give a reason
    The bottom pic is the dispute
    The first pic is the ppt
    Thank you
     
    Last edited by a moderator: Nov 6, 2016
  2. jcsd
  3. Nov 6, 2016 #2

    phinds

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    Is there some reason you posted these sideways? I don't know about others but I'm not willing to get a kink in my neck. When you are asking someone to do you a favor by looking at your work, it's not a good idea to make it difficult for them.
     
  4. Nov 6, 2016 #3
    Sorry I posted these from a phone. I'll correct it
     
  5. Nov 6, 2016 #4
    Ask yourself, "what is it that happens when a hydrocarbon is cracked?" There is only one answer that is true for all cracking.
     
  6. Nov 6, 2016 #5

    Borek

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    Answer is D wrong. Actually I am not convinced any of these answers is correct.

    And you have no idea how long it took me to calm down and to not post what I think about the _teacher_ stating cracking produces polymers.
     
  7. Nov 6, 2016 #6

    phinds

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    The first two answers given by Google when I Googled "what is it that happens when a hydrocarbon is cracked" were:

    Cracking is the name given to breaking up large hydrocarbon molecules into smaller and more useful bits.

    Which is exactly answer A. Why do you not think that is correct? Have I fallen into the trap of thinking the Internet is right in this case? I know the internet is wrong in a lot of cases but this certainly SOUNDS right.
     
  8. Nov 6, 2016 #7
    The use of "fractions" is probably not the best way to put it, but cracking does break up a longer molecules into smaller parts that can be all monomers, all polymers or a mix of the two. It all depends on what's being cracked. and why. Answer A was the only one that works.
     
  9. Nov 6, 2016 #8
    http://www.goffs.herts.sch.uk/documents/science/as_chem/unit2_f322/alkanes/cracking.ppt
    This is where the original presentation was found
    If the presentation is downloaded and opened in PowerPoint then the answer is C
    But if it's opened in a Mobile device like iPhone, then the answer sort of varies over D and C
    I guess the teacher is fixated on that and says its D
    But we cannot say D cause it produces monomers which can be used in polymer production but the product is NOT a polymer right?
     
  10. Nov 7, 2016 #9
    I think I misspoke about polymers possibly being products. I recalled (incorrectly) that some complex/long molecules remained after the natural cracking of hydrocarbons in oil samples. Answer C is most probably true, based on cracking chemistry in the petrochemical industry, but it also seems that Answer A is true in a less scientifically-worded way. All I ever did was look for the hydrocarbons in the ground. I never had to ponder and worry over what was done with stuff later. Thanks for this learning experience.
     
  11. Nov 7, 2016 #10
    Thank you very much
    It says in the notes of the presentation that the product ethene is used to make plastics and the other product hydrogen is used in haber process
    But based on that we cannot say that cracking produces ammonia and plastics
     
  12. Nov 7, 2016 #11

    Borek

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    No, it is not exactly answer A. Unless my English fails me, separation means a process like distillation, in which you not _break_ molecules into smaller ones, but _separate_ mixture of different molecules into pure components (or at least fractions that contain a mixture of similarly boiling components). First process involves breaking intramolecular bonds, the other does not. That's especially important difference in the case of petrol industry, where both processes - cracking and separation - are used. Typically cracking is followed by a separation.

    And while C does look plausible, it is not always true. Yes, catalytic cracking uses a catalyst, but thermal cracking (which was the original process that gave the name to the procedure) does not. They both fit the general "cracking".

    Judging form the pencil notes whoever was approaching the answers on the second picture mistook cracking for polymerization and tried to answer a completely different question.
     
  13. Nov 7, 2016 #12
    Thank you very much everyone
    It has being decided that as the power point presentation showed, choice C is the best one in this case
    I thank you all for your input
    I had fun
     
  14. Nov 7, 2016 #13

    phinds

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    Although "separation" is a vague term that can be construed many ways, I believe your distinction is correct in this case. Thanks for that correction.
     
  15. Nov 7, 2016 #14
    It isn't C. I was looking at the wrong set of answers. Cracking does not have to use a catalyst, but does involve saturated molecules. Looking at the proper set of answers, now that I'm reasonably sentient, if C is correct, then B is also correct. Neither is true for all cracking. Using the term "separation" does rule out A. In the end, this was a bad multiple-choice question.
     
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