DAT Destroyer- G-chem #123

toothteethtooth

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Dec 5, 2013
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    In this problem, they have done an ICE table for the Kp Problem. I understand that Kp is to be calculated the same way as other K constants such as Ksp and etc. However, in the solutions, they did an ICE table to solve for the Kp They have not canceled out the "X" amount from A or B (both reactants) as it was always considered negligible when I did the Ksp Problems. Chad's videos also shows that X is really low compared to the given concentrations so you cross it out and solve for the rest. In Destroyer, the negligible X amount in the calculation is kept in the answer until the end and solved for. This is a little different than doing calculations for the Ksp ICE table. Can anyone explain me the difference on why X was not considered negligible in this?

    I hope I make sense, if not I apologize. DAT in 15 days so I am kind of going crazy!!!!
     

    Pearl E. White

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    May 20, 2014
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    1. Dental Student
      In this problem, they have done an ICE table for the Kp Problem. I understand that Kp is to be calculated the same way as other K constants such as Ksp and etc. However, in the solutions, they did an ICE table to solve for the Kp They have not canceled out the "X" amount from A or B (both reactants) as it was always considered negligible when I did the Ksp Problems. Chad's videos also shows that X is really low compared to the given concentrations so you cross it out and solve for the rest. In Destroyer, the negligible X amount in the calculation is kept in the answer until the end and solved for. This is a little different than doing calculations for the Ksp ICE table. Can anyone explain me the difference on why X was not considered negligible in this?

      I hope I make sense, if not I apologize. DAT in 15 days so I am kind of going crazy!!!!
      What version of Destroyer is this? I have 2017 and my 123 is a cell potential question. Let me know and I will try to help.
       
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      orgoman22

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      1. Non-Student
        In this problem, they have done an ICE table for the Kp Problem. I understand that Kp is to be calculated the same way as other K constants such as Ksp and etc. However, in the solutions, they did an ICE table to solve for the Kp They have not canceled out the "X" amount from A or B (both reactants) as it was always considered negligible when I did the Ksp Problems. Chad's videos also shows that X is really low compared to the given concentrations so you cross it out and solve for the rest. In Destroyer, the negligible X amount in the calculation is kept in the answer until the end and solved for. This is a little different than doing calculations for the Ksp ICE table. Can anyone explain me the difference on why X was not considered negligible in this?

        I hope I make sense, if not I apologize. DAT in 15 days so I am kind of going crazy!!!!

        When you are solving an acid base problem that involves a Ka or Kb......even a Ksp problem, we will always neglect the x in the denominator. We do this because we are assuming that only a small amount has dissociated or ionized. Without this assumption, a quadratic would be needed. The DAT exam will have calculations in which the approximation holds nicely. I have written up two questions using the ICE table....where you have INITIAL amounts of reactants in an equilibrium expression. The numbers are easy to work with, and although not likely to appear on the exam, it is good practice.

        Hope this helps.

        Dr. Romano
         
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