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Mo' chemistry problems

Discussion in 'Pre-Dental' started by ibo man, Aug 29, 2002.

  1. ibo man

    ibo man Senior Member
    10+ Year Member

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    Please help!!
    When 14.250 moles of PCl5 gas is placed in a 3.00 Liter container and comes to equilibrium at a constant tempreture, 40% of the PCl5 decompose according to the equation.

    PCl5 <------> PCl3 (g) + Cl2 (g)
    what is the value of kc for this reaction
    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 the above.
    The correct answer to this problem is A.

    If you have a solution of 1L of H2O and 234 (g) of NACl. What is the osmotic pressure at STP. (R=0.1L *atm/mol*K)

    A). 89.54 atm.
    B). 109.2 atm.
    C). 146.61 atm.
    D). 218.4 atm.
    E). 234.0 atm.
    The correct answer to this problem is D.

    What volume of HCL was added if 20 ml of 1M NaOH is titrated with 1M HCL to produce a PH=2

    A). 10.2 ml
    B). 20.2 ml
    C). 30.4 ml
    D). 35.5 ml
    E). None of the above.
    The correct answer to the above problem is E.

    I'll appreciate very much if you can help explain this problems to me, and others who doesn't understand the questions. Thanks very much.
     
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  3. ibo man

    ibo man Senior Member
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  4. mzalendo

    mzalendo Member
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    I realize that Ibo man may be taking the Dat tommorow. Here are the answers to your previous query.Hope they will be of help.
    PCl-------- --PCl3 + Cl2
    Initial 14.25/3 0 0
    change -.4(14.25/3) +.4(14.25/3) +.4(14.25/3)
    final .6(14.25/30 .4(14.25/3) .4(14.25/3)
    2
    Kc={pcl3][cl2)/[Pcl5)
    = 1.896^2/2.854

    Osmotic pressure =MRTi
    4x0.1x273x2(since it is electrolytic)
    =218.4
    3
    volume of acid =x
    volume of base =0.02
    I will add base to excess acid instead
    remaining moles of acid due to neutarlization =
    x-0.02
    the total volume of rxn =x+0.02
    we know that given the pH that
    x-.02/(x+.02)=10^-2
    x=20.4ml hence none of the answers

    Good luck and tell me about your experience
     

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