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Help for Chem Problem,

  1. Oct 24, 2007 #1
    1. The problem statement, all variables and given/known data


    0.2500 g sample of an Aℓ-Zn alloy reacts with HCℓ to form hydrogen gas:
    Aℓ(s) + 3H+(aq) → Aℓ3+(aq) + 3/2H2(g)
    Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g)
    The hydrogen produced has a volume of 0.147 L at 25°C and 755 mm Hg. What is the
    percentage of zinc in the alloy?

    2. Relevant equations

    PV=NRT



    3. The attempt at a solution


    Frist I start out finding the number of moles of Hydrogen gas produced by using PV=NRT
    N=((.993atm)(.147L))/((.0821)(298K))= .00596 mol of H2
    1mol of Al = 26.98g
    1mol of Zn = 65.93g
    now what should I do?
    Help please.
     
  2. jcsd
  3. Oct 24, 2007 #2

    chemisttree

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    Well, you know that the sum of the masses of aluminum and zinc is 0.250 g. Let x = mass of aluminum in the alloy and y = mass of zinc in the alloy.

    x+y=0.250

    but

    y = 0.250 - x, so the mass of zinc in the alloy is 0.250 g - x

    You also know the number of moles of aluminum in the sample of the alloy is x/26.98 and the number of moles of zinc is (0.250 - x)/65.93. Can you take it from there?
     
  4. Oct 24, 2007 #3
    I know about that but how do you calculate the mol of Zn by using .00596mol of H2 I found in the gas law.
     
  5. Oct 24, 2007 #4

    chemisttree

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    Do you know of a relationship between the number of moles of Al and the number of moles of H2 produced from it's treatment with HCl? Do you know of a relationship between the number of moles of Zn and the number of moles of H2 produced from it's treatment with HCl? If you add the hydrogen produced from Al to the hydrogen produced from Zn how much will you have?
     
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