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AP Chemistry Test / Solubility Rules

  1. May 9, 2009 #1
    I'm finding a lot of inconsistency with the solubility rules from different sources.

    especially when it comes to SO4(negative 2 charge).

    my teacher told me: soluble except when combined with Ca2+, Ba2+, Sr2+, Pb2+... however, other sources sometimes include Hg(II) 2+, and some Ag+, and some both Hg(I) and (II).... so confusing.

    any ideas?

    also... not as important, but what is the format of the AP test?
    I know its 75 MC and then 6 FRQs, but how much are the MC and FRQ sections scaled? And also, it seems that each FRQ varies in points?
     
  2. jcsd
  3. May 10, 2009 #2
    Insoluble sulphates (in order from the most insoluble to the least insoluble):
    Ra2+, Ba2+, Pb2+, Sr2+, Hg22+, Ca2+, Ag+.
    Their pKsp:
    10.4, 10.0, 7.7, 6.5, 6.2, 5.0, 4.8
     
  4. May 10, 2009 #3
    Thank you very much, lightarrow!
     
  5. May 10, 2009 #4

    Borek

    User Avatar

    Staff: Mentor

    You see, the problem is that soluble/insoluble is not zero or one, it is governed by Ksp - so you have to put the limit somewhere. CaSO4 is considered insoluble, but saturated soluition is about 0.005M - not bad for "insoluble" salt. For Ag2SO4 saturated solution has even higher concentraion.
     
  6. May 10, 2009 #5
    http://www.collegeboard.com/student/testing/ap/chemistry/samp.html --> Sample F/R Questions

    Good luck!:biggrin:
     
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