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another chem question

Discussion in 'DAT Discussions' started by pistolpete007, Jun 3, 2008.

  1. pistolpete007

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    150 ml of a 3 M KCL solution is diluted w/ 500 mL of distilled water. The the resulting solution is stirred and 300 mL are poured out of the beakr. what is the molarity of the remaining solution.

    a.3 x 150/500
    b.3 x 500/150
    c.3 x 300/150
    d. 3 x 150/300
    e 150 x 3/650
    ok so the 300ml that is poured out is pretty much negligable....so i thought you would just do M1V1=M2V2 and the answer would be A....but that is not the case for some reason.....in theis one they did M1V1/(V1+V2)....which would be E WHY IS THIS?!??!?!?!?

    why did they add both the ml together.....i can kind of see why but now i am really confused.....when do I add the volumes together....and wehn do i do straight up M1V1=M2V2 by the information they gave me...bc a lot of questions when they give u both the volumes and one of the molar concentration u just plug it in....u dont add the 2 volumes for V2...PLEASE HELP and if im missing something here can u please give me an example of what to do when?
     
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  3. doc toothache

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    Did the problem state that the solution was diluted with 500 ml of distilled water or to 500ml with distilled water?
     
  4. Optimism Smiles

    Optimism Smiles DAT drains my ATP
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    It is a type of m1v1=m2v2 problem, I believe. Just think about the problem logically for a moment. M1V1 (which is 3M x 150mL) is obviously what you start with. Think about what the word "diluted" means. It means adding water to something to make it less concentrated. Since the KCl is diluted with 500 mL of water, this means 500mL of water is added to the initial KCl solution (150 mL) in order to make it less concentrated. Therefore the FINAL volume would be the starting 150mL PLUS the added 500mL of water. You get that the final volume would be 150mL + 500mL = 650mL. So if you rearrange the equation, you get m2 = (3M x 150mL)/(650mL).

    I think it is important to not just memorize formulas, but understand each situation and how to apply the formulas to them. Do you now understand why V1 and V2 were added? I hope this helped!! :)
     
  5. Sea of ASH

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    since you started out with 150ml of KCl and you add 500ml of water, your total (or final) volume is 500+150 = 650.

    remember the formula is really MiVi = MfVf
     
    #4 Sea of ASH, Jun 3, 2008
    Last edited: Jun 3, 2008
  6. DentalDeac

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    Looks like someone needs to work on a little QR ;)
     
  7. Sea of ASH

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    i dont understand what your talkin about??? :rolleyes: ;)

    hahahahha good eye
     
  8. pistolpete007

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    thanks a lot y'all that really helped....but if it says diluted TO...500ml then i dont add the 2 volumes together right?
     
  9. Optimism Smiles

    Optimism Smiles DAT drains my ATP
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    By adding the word "to" it assumes the final volume would be just the 500mL (don't add the 150mL to it).
     
  10. doc3232

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    Haha, it happens to the best of us.
     

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