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What Is The Mass Percent?

A sample weighing 14.98g and containing a small amount of copper was treated to give a solution containing aqueous Cu^2+ ions.  Sodium iodide was then added ti yield solid copper (I) iodide plus I3^- ion, and the I3^- was titrated with thiosulfate, S2O3^2-.  The titration required 10.49mL of .100M Na2S2O3 for complete reaction.  What is the mass percent copper in the sample?  The balanced equations are…

2Cu^2+(aq)+5I^-(aq)—->2CuI(s)+I3^-(aq)

I3^-(aq)+2S2O3^2-(aq)—->3I^-(aq)+S4O6^2-(aq)

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Posted on October 1, 2013, in #question and tagged , , , , , , , , , , , . Bookmark the permalink. 1 Comment.

  1. .1M(.01049L) = .001049 mol S2O3^2-
    .001049mol(1mol/2mol)(2mol/1mol) = .001049mol Cu^2-
    .001049mol (63.55gCu/1mol) = .06666g Cu^2-

    mass % = (.06666gCu^2-/14.98g) (100) = .4450% Cu

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