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Chemsitry - Moles Consumed

  1. Apr 20, 2009 #1
    1. The problem statement, all variables and given/known data

    The overall chemical equation for the titration reaction is:
    OCl(aq) + 2 S2O3(aq) + 2H+(aq) 6 Cl(aq) + S2O6(aq) + H2O(R)

    If a titration requires 5.29 ml 0.256 M Na2S2O3,
    (i) how many moles of S2O32&(aq) were consumed in the titration, and
    (ii) how many moles of OCl&(aq) were in the sample?


    2. Relevant equations



    3. The attempt at a solution

    Ok so what i did was take .245/52.9 and multiplied it by 2 to get .0096 moles of S2O3 consumed....is that right?
     
  2. jcsd
  3. Apr 21, 2009 #2

    Borek

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    Staff: Mentor

    No.

    Try to explain what you did and why.

    And using numbers that were given in the question won't hurt.
     
  4. Apr 21, 2009 #3
    I just realized there is supposed to be an arrow in between the 2H and the Cl; that is where the equation splits into reactants and products.

    I'm looking over it again and trying something different. I messed up in the math the first go around

    .256/.00529 L = 48.4 mols X 2 (because there are 2 mols S2O3) and that gives me 96.8 mols S2O3; part i

    Shouldn't part (ii) just be the 48.4 mols from the previous?
     
  5. Apr 21, 2009 #4

    Borek

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    Staff: Mentor

    You are still wrong. Check your units.
     
  6. Apr 21, 2009 #5
    M = mols/volume

    I know M and the volume, so it should be M * volume..not divided..right?

    .256 * .00529 = .00135

    .00135 * 2 = .0027 mols. Is that right?
     
  7. Apr 21, 2009 #6

    Borek

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    Staff: Mentor

    Better, but still wrong. You got concentration&volumes&moles part right. Why do you multiply by two if you are calculating number of moles of S2O32-?
     
  8. Apr 21, 2009 #7
    I multiplied by 2 because there are 2 S2O3 in the equation. Doesn't that mean you multiply it by two so that your ratio is correct?
     
  9. Apr 22, 2009 #8

    Borek

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    Staff: Mentor

    Think about it - you put a mole of substance into the baker, but as reaction equation have a 2 in the equation, that means you put 2 moles in the baker? That's what you did now.
     
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