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Solubility Rules

Discussion in 'DAT Discussions' started by osimsDDS, Jun 15, 2008.

  1. osimsDDS

    osimsDDS 5+ Year Member

    Jun 8, 2007
    I have always wanted to make a thread for this because I never understood this until NOW: Solubility rules are pretty important for those who want to get a good score on the gchem section because I believe those will be the trickiest on the test...they have to do with acidity, solubility, etc...

    Here they are, first the basic rules:

    1) Any alkali metal cations and ammonium (NH4+) ion are soluble
    2) All compounds containing NO3-, ClO4-, ClO3-, and C2H3O2- anions are soluble.
    3) All chlorides, bromides, and iodides are soluble except those containing Ag+, Pb2+, or Hg2^2+.
    4) All sulfates are soluble except those containing Hg22+, Pb2+, Sr2+, Ca2+, or Ba2+.
    5) All hydroxides are insoluble except compounds of the alkali metals, and Ca2+, Sr2+, and Ba2+.
    6) All compounds containing PO43-, S2-, CO32-, and SO32- ions are insoluble except those that also contain alkali metals or NH4+.

    Let me give an example of an important question that was posted yesterday that has to do with acidity...

    ex) Why are FeCl3 and AlCl3 acidic in water?
    To answer this question we would first have to know how these react with water, they both form hydroxides that are bound to the metals Fe and Al (FeOH3 and AlOH3). Now from our rules we know hydroxides are insoluble and therefore both the hydroxides will precipitate in solution. Since we reacted OH- from water we have another H+ left, this will most definitely be in solution causing it to be ACIDIC!!! The OH- ion will not be in solution because it is not soluble and will precipitate not forming a base. Definition of an Arehnius base is one that gives up OH- in solution, but the metals hydroxides can not...I like this question it really tests your knowledge...

    Anyone that knows anymore rules post em up, thanks...
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  3. lphiewok

    lphiewok ACFAS Member 7+ Year Member

    Aug 19, 2007
    Fort Polk, LA
    wow great post. man you need to just take your DAT already
  4. Hugh Mannity

    Hugh Mannity 2+ Year Member

    May 15, 2008
    I didn't have one question where I had to know what precipitated out. I did have solubility problems but it was not like, what is the species that is insoluble. It was applications of solubility. I think your going way overboard, but I guess it's better to be over-prepared than under-prepared.
  5. sweetpea2

    sweetpea2 2+ Year Member

    Apr 21, 2008
    Where the solubility questions you had involved..or just like..given a few solubilities..rate the solubilities of a few compounds?
  6. osimsDDS

    osimsDDS 5+ Year Member

    Jun 8, 2007
    im speaking more in general, like hugh Manity said, most of these questions will be conceptual and you need to apply them...but its a good thing to know in general...I gave an example in the thread

    DRHOYA 2+ Year Member

    May 15, 2008
    True, and alot of times you can rule out wrong answers by knowing the solubility rules, and then applying them to obviously wrong answers. The practice questions I have come accross have been along the lines of basic ie: "which of the following is MOST soluble in water", "which is LEAST soluble in water", and having to apply the rules to a rxn mechanism.

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