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posted by  fhogg001 on 11/19/2008 10:17:59 PM  |  status: Closed  

will rate lifesaver - general chem question - determining molarity

Course Textbook Chapter Problem
General Chemistry N/A 20 N/A
Question Details:
A BaSO4 slurry is ingested just before an x-ray of the gastrointestinal tract is taken because the precipitate is opaque to x-rays and thus defines the contours of the tract. The Ba2+ ion is toxic but the compound is nearly insoluble. ΔG* at 37*C (body temperature) is 59.1 kJ/mol for the process below.
 
                                       BaSO4(s)    Ba2+(aq) + SO42-(aq)
 
What is [Ba2+] in the intestinal tract? (Assume the only source of SO42- is the ingested slurry.)
__________M
~ Neal
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posted by Werner on 11/20/2008 5:46:28 AM  |  status: Live
Asker's Rating: Lifesaver   
fhogg001's comment:
"Thank you"
Response Details:
  Given that
   BaSO4(s)    Ba2+(aq) + SO42-(aq)
    ΔG0 = 59.1 kJ/mol
  We know that
    ΔG0 = -RTlnKsp
  lnKsp  = - (ΔG0 /RT)
             = -(59.1 kJ/mol / (8.314*10-3 kJ/mol.K)(310K))  
             = -22.93
      Ksp = e-22.93
              = 1.1*10-10
       Ksp = [Ba2+][ SO42-]
  ∴   [Ba2+] = √Ksp
                    = √ 1.1*10-10
                    = 1.05*10-5 M 
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