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Homework Help: Redox Reaction (An Easier Way?)

  1. Dec 23, 2012 #1
    1. The problem statement, all variables and given/known data
    From 9th edition of Raymond Chang's Chemistry (Problem 4.108):
    "When 2.50 g of zinc strip were placed in a AgNO3 solution, silver metal formed on the surface of the strip. After some time had passed, the strip was removed from the solution, dried, and weighed. If the mass of the strip was 3.37 g, calculate the mass of Ag and Zn metals present."

    2. Relevant equations
    [itex]Zn + 2AgNO_3 \rightarrow 2Ag + Zn(NO_3)_2[/itex]

    3. The attempt at a solution
    I'm, honestly, more of a math person. Because it was indicated that the reaction was not exactly like the chemical equation above (id est, not all the zinc was made into zinc nitrate), I decided I'd make a mathematical equation to represent it.

    Thus, I came to [itex]M_{Ag}\left(2(m_{Ag} - m_{Zn})\right) + M_{Zn}m_{Zn} = 3.37[/itex], where M is the molar mass of the respective element, mAg is the theoretical number of moles of silver if all the zinc was made into zinc nitrate, and mZn is the actual number of moles of zinc remaining on the strip. Solving for mZn, we get 0.0324456474... mol Zn. Thus, the mass of Zn is around 2.12 g, and therefore the mass of Ag is around 1.25 g. This is the correct answer given in the back of the book.

    The question is: "Is there an easier way?"
  2. jcsd
  3. Dec 23, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    There's no rule that says you can't mix math and chemistry.

    You have solved the problem in a simple and efficient way.
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