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reaction question

Discussion in 'MCAT Study Question Q&A' started by afatasstank, 01.30.10.

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  1. afatasstank

    afatasstank

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    Consider this reaction:
    Fe3+(aq) + Cl-(aq) <===> (FeCl4)-(aq)
    Yellow .............................Colorless

    Explain what would happen to the color of a dilute solution containing (FeCl4)- if
    a. you added a solution containing silver ion, Ag +. (silver ion reacts with chloride ion in solution to form the precipitate AgCl.)

    b. you added concentrated HCl

    c.you added concentrated H2SO4

    thanks guys.!!:xf:
    Last edited: 01.30.10
  2. unique135

    unique135

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    From my understanding,
    1. Enough Ag+ takes away Cl- forming precipitate AgCl. Equilibrium of the solution is disturbed because Cl- ions are removed. Thus, the equilbrium will shift towards left to produce Cl- ions. But, the enough of Ag+ would keep taking away Cl- until there is no Cl- ions left. At this point, there will be FeCl4- or Cl- ions. Only thing left will be Fe3+ ion which would have yellow color (I had to check on color).
    2. Addition of HCl will again give extra Cl- ions, thus disturbing the equilibrium. Equilibrium will shift towards the right producing more FeCl4-. Overall, equilibrium will be attained and color will be yellow as well.
    3. Addition of H2SO4 will not affect the equilibrium since it doesn't have any common ion present. Thus, color remains same (yellow).
    This is what I understand. I could be wrong.
  3. afatasstank

    afatasstank

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    sorry, it took out the spaces between "yellow" and "colorless" so i edited it.
    now that that is cleared up, does it make a difference to your answer unique?
  4. unique135

    unique135

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    I think FeCl4- solution is yellow in color. Need verification for this though.
  5. afatasstank

    afatasstank

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    the question wrote on here is the exact same as on the sheet, so they tell you that (FeCl4)- is colorless

    so wouldnt that make b. colorless
  6. unique135

    unique135

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    In that case,

    For B, it would range from light yellow to colorless because of more FeCl4- (The color of the solution will depends on the concentration of different ions present in the solution)

    With enough of HCl added to the solution, at certain point, all of Fe3+ ions are used up then the solution will be colorless.

    This is so far obvious.

    --------------------------------------------
    In details, I found that many other complex ions are formed from these products and they have higher formation constant. Overall, other complex ions such as FeCl2- which, I believe, has highest formation constant will likely show up before FeCl4-. Since I am not a chemist and MCAT will get into such depth, I wouldn't worry about this part.
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