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Chemistry HELP!!!!!

Discussion in 'DAT Discussions' started by waitingame, Jun 4, 2008.

  1. waitingame

    2+ Year Member

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    Ok so I just have a few things that I cant keep straight. I dont understand if they give you one molecule how are you suppose to know if it is an Arreheious acid/ base, Lewis acid and base or Bronstead acid or base especially if they only give you one molecule such as BF3 (more general question not what BF3 is because I know it is Lewis) and I know the general definitions just dont understand how to use the definition to tell which it is.

    Also I am having some trouble with two things and knowing when to use each. I dont know if they go with acid or ksp's or what. So there are two different problems 1. use (x^2/ M of reactant) = molarity of overall.
    2. you can use the short cut 27x^3, 4x^2 or x^2.

    I dont know when each are used and I know it is very vague but that is to the point that I understand it and need help drastically because I know that they will be a question on the test and need every question.
    I know it sounds dumb but it is something I just cant get a grasp on and examples would be great. Thanks:D:D:D
     
  2. TempleDMDKrazd

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    Arrehenious (spelling might be wrong)
    Acid: gives off a proton (H+)
    Base: gives off a hydroxide (OH-)

    Bronsted-Lowry
    Acid: donates proton (H+)
    Base: Can accept a proton (H+), basically anything that has a lone pair that can be protenated

    Lewis
    Acid: Electron Pair acceptor (BH3, ACl3, etc)
    Base: Electron Pair donator (NH3)
     
  3. waitingame

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    Anyone have any clue what I am talking about for the second part?
     
  4. waitingame

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    Alright so I figured out one part .... it comes from acid base

    example: CH3COOH arrow H+ + CH3COO- given Ka= 1.8X10-5 in a 2M solution
    so I would use 1.8X10-5 = x^2/ 2

    Now what would happen if it dissociated into say 2 moles of one and one mole of the other would it be 2(x^2)/2?

    And I still dont know what the other part is if anyone could help the short cut is MX--- KSP= x^2 MX2----KSP= 4x^3 MX3----- KSP= 27x^4
    Can anyone explain when I use this? and tell if I was correct for the first part if there are two moles? Thanks
     
  5. osimsDDS

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    For the Ksp thing you use that for when your trying to find out the concentrations...you are right MX=x^2, MX2=4x^3 and so on.

    I am pretty sure you use these to find the concentrations of the elements in the compound as well as the compound itself given that the moles are the same...

    ex/ MP2 ------> M^2+ + 2P^- (I am using P for explanation sake)

    They will give you Ksp= some number like 4.2x10^-10
    Then you know 4x^3=Ksp so you solve for x which is the concentration...
    Now if they ask for the concentration of P, since its two moles you just multiply by 2.

    Hope this is right and hope it helps if it is right haha
     

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