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Random Questions =) Any help appreciated!

Discussion in 'MCAT Study Question Q&A' started by whoknows2008, Jun 17, 2008.

  1. whoknows2008

    whoknows2008 7+ Year Member

    May 27, 2008
    Since SDN is awesome, and you guys are awesome, I hope you'll help me out again! Here are my questions:

    -What are the most important VESPR geometries to know? There are so many!

    -Does anyone have a trick to memorizing the solubility rules?

    -Gen Chem, Quantum Mechanics - how much detail to we need to know?

    -Org. Chem, Meta, Para, Ortho Directors - are there common ones we should know?

    ...Clearly trying not to fill my brain with aimless info! :laugh:...

    Thanks in advance!!
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  3. Quantum Chem

    Quantum Chem 2+ Year Member

    Jun 10, 2008
    College Park, Md
    I don't really know what you should know specifically, but...

    I think that the basic VSEPR geometries (linear, trigonal-planar, tetrahedral, ...) would be needed. As for the special names within each basic geometry, you could memorize them or use basic chemistry and determine the shape. Just remember that electron pairs will be in places experience the least amount of repulsion from other electron pairs and bonding electrons. Using that knowledge you can determine how the bonding pairs will be placed and could determine the name.

    For Quantum mechanics I would assume that basic quantum numbers should be understood (n, l, ml, and ms). Probably should know Hund's rule and Pauli exclusion principle. I can't imagine that the MCAT will want an in depth knowledge of quantum mechanics, but more of a general understanding which you probably learned in gen chem I.

    For solubilities, I believe that there is a general trend and exceptions. I don't really know it off the top of my head, it is easily found in a gen chem book.

    For O,M,P directors it is really easy to remember that anything directly attached to the ring that has free electrons will donate (Ortho, Para directors), but its ability to donate decreases as electron withdrawing groups are attached to the oxygen (ie, Phenyl Acetate). Anything with a positive charge is M director (NO2), which can be tricky to see if the structure isn't drawn or you just know it has a positive charge. Any carbon bonded to the ring that is also bonded to an oxygen will be Meta directing. Halides are Ortho, Para directors, but are ring deactivators.

    Not really aimless info. Surely the repetition from classes and studying gets it to stick in your brain, just understanding why this or that happens is might be more useful. But then again I love chemistry, so it could just be me.:D
  4. Kaustikos

    Kaustikos Archerize It 7+ Year Member

    Jan 18, 2008
    Always Bespin
    Awesome post. :thumbup:

    For solubility rules, as stated, varies. But the basics to know and build upon:
    All salts of alkali metals are soluble
    All Chlorides/Bromide/Iodide salts are soluble EXCEPT Ag/Pb/Mg/Hg/Cu
    All Sulfates are soluble except Pb/Ag/Ba/Sr/Ca
    Salts of Hydroxides are insolube with exception of Alkali or certain alkaline earth metals (Calcium, Strontium and Barium - I'd actually remember these guys if I could, they tend to be the rule breakers in solubulity rules and I did see a question relating to that)

    All salts of Sulfides, Carbonates and Phosphates tend to be insoluble

    I think that's all. Thanks to Kaplan for that.:laugh:
  5. whoknows2008

    whoknows2008 7+ Year Member

    May 27, 2008
    Thanks! :) The help is greatly appreciated!

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