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Homework Help: Weight percent and concentration problem

  1. Aug 26, 2009 #1
    the question is at below.

    320ml of 29wt% of ammonium hydroxide
    1210ml of 31wt% of hydrogen peroxide
    30190ml of water

    mixed together.

    What is the concentration of ammonium hydroxide and hydrogen peroxide now?
    Is there any reaction occurs between them?
  2. jcsd
  3. Aug 26, 2009 #2


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    Homework Helper

    Welcome to PF!

    Hi shiyao85! Welcome to PF! :wink:

    Show us what you've tried, and where you're stuck, and then we'll know how to help! :smile:
  4. Aug 26, 2009 #3
    Conversion of weight percent to molarity

    Where Cw is weight percent
    Mw is molar mass
    M is molarity
    ρ is density of the solution

    Assumption: -No reaction between ammonium hydroxide and hydrogen peroxide

    -Hydrogen peroxide
    Density = 1.44g/mL
    Cw = 31wt%
    Mw = 34g/mol
    From *
    V1 = 1210ml = 1.21L

    -Ammonium hydroxide
    Density = 0.9g/mL
    Cw = 29wt%
    Mw = 35g/mol
    From *
    M2 = 0.0745mol/L
    V2 = 320ml = 0.32L

    After mixing:
    Total volume of the solution is 31.72L.
    Formula for dilution
    MiVi = MfVf

    For ammonium peroxide
    MiVi = MfVf
    (0.0745mol/L) X 0.32L = Mf X 31.72L
    Final molarity of NH4OH in the solution is 7.51X10^-4 mol/L.

    For hydrogen peroxide,
    MiVi = MfVf
    (0.131mol/L) X 1.21L = Mf X 31.72L
    Final molarity of H2O2 in the solution is 5X10^-3 mol/L.

    Density of the substances from internet

    I was stuck in the part of final volume. Not sure one which the number i should use. Is it total volume of the solution? or just the volume of the chemical and water?
  5. Aug 27, 2009 #4


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    Staff: Mentor

    Sum masses of all solutions and assume density to be that of pure water (mass is conserved after all, which can't be said about volume). You won't find anything better and the final solution seems to be quite diluted.

  6. Aug 27, 2009 #5
    So have to convert the total volume to mass rite? assume the density to be 1 for all the solute also rite? because all of them are quite dilute..
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