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S'more DAT questions!!!

Discussion in 'Pre-Dental' started by portlander, Aug 9, 2002.

  1. portlander

    portlander Member
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    1) A tick bird on a rhinosaurus is an example of what type of symbiotic relationship?

    A. Commensalism
    B. Mutualism
    C. Parasitism
    D. Saprophytism
    E. Insectism

    Answer key says 'B'. I am not an ecology person, but I put 'A' because commensalism means one organism gets a benefit while the other is neither harmed nor helped. In what way is a rhino benefiting from the 'tick bird'? Is that information something I would have had to know beforehand?

    2) When 14.250 moles of PCl5 gas is placed in a 3.00 liter container and comes to equilibrium at a constant temperature, 40.0% of the PCl5 is decomposed
    PCl5 (g) ------------> PCl3 (g) + Cl2 (g)
    What is the value of Kc??

    A. (1.896)^2 / (2.854)
    B. (2.854)^2 / (1.898)
    C. (3.800)^2 / (2.854)
    D. (2.854)(1.896) / (3.800)
    E. None of these

    The answer key says 'A'. I know that Kc is = to
    [PCl3][Cl2] / [PCl5], and that concentrations of PCl3 and Cl2 are equal, and that the concentrations should be measured in atms, but I cannot make the numbers work out. How do you figure out the pressures??

    Thanks so much for whoever can help!

    Taking my DAT 3 weeks from today!!!
     
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  2. nycdoc

    nycdoc Senior Member
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    The tick bird is eating the ticks therefore the rhino is benefitting because it no longer has ticks. The bird is getting food, the rhino is getting groomed. Mutual relationship=mutualism
     
  3. Dentalstu02

    Dentalstu02 Member
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  4. OP
    OP
    portlander

    portlander Member
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    Thanks so much!!

    I have one more:

    The 1H NMR of which of these compounds will show only 2 singlets?

    A. CH3-CH2-O-CH2-CH3
    B. H3C-O-{phenyl}-O-CH3

    The answer is 'B'. I can see how both of these might get two singlets, but I haven't had Orgo in a long time. Why is 'A' wrong?
     
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  5. DesiDentist

    DesiDentist G. S. Khurana, DMD, MBA
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    think of the tick question in this way.

    A tick is a parasite, so if a tick bird is eating the parasite it is helping the rhino. Thus both are being helped.

    DesiDentist
     
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  6. ItsGavinC

    Dentist Moderator Emeritus 15+ Year Member

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    portlander,

    For the Organic question, you can apply the "n+1" rule in a general manner. That is, "n" Hydrogen atoms are going to give n+1 peaks.

    You can instantly see that CH3-CH2-O-CH2-CH3 will have more than "only two singlets".
     
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  7. DATMATT

    DATMATT SISU
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    I believe the statement that

    "CH3-CH2-O-CH2-CH3 will have more than only two singlets". Should be clarified. It will not have any singlets. It will have 2 quartets and 2 triplets.

    Matt
     
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  8. vixen

    vixen I like members
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    I agree Matt...a 4H quartet and a 6H triplet.
     
  9. sjdent

    sjdent Senior Member
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    Portlander,

    You know what one of the happiest (and scariest) things about taking the DAT is?

    Happiest: knowing you'll never have to remember facts from crappy subjects like G. Chem.

    Scariest: knowing it's that easy to forget facts from crappy subjects like G. Chem. I swear I've forgotten all that stuff, from O. Chem to G. Chem. Yikes.
     
  10. DesiDentist

    DesiDentist G. S. Khurana, DMD, MBA
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    tell me about it. I never paid attention in Ochem, now I'm crapping my pants. I just crammed and that was the biggest mistake of my life...but I still did decently.

    To all of those who haven't taken ochem, but planning to. Take your time and absorb this material like a sponge. You will thank yourself later. Trust me.

    DesiDentist
     
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