Percent Composition

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Homework Statement


An alloy of copper and silver weighing 0.5000 grams is dissolved in HNO3 and treated with H2S to precipitate both CuS and Ag2S. It is found that the solid sulphides weigh 0.7300 grams. Calculate the percentage of Ag in the alloy. (12.9 %)

2Ag+(aq) + H2S(aq)→ Ag2S(s) + 2H+(aq)
Cu+2(aq) + H2S(aq)→ CuS(s) + 2H+(aq)


Homework Equations


mass of Ag/mass of alloy = % of Ag

The Attempt at a Solution


I'm not too sure how to start this question…

So far, I have

0.7300 g Ag2S x 1 mol / 215.74 g Ag2
= 2.945 x 10-3 mol Ag2S

2.945 x 10-3 mol Ag2S x 215.74 g Ag2/ 1 mol Ag2S
= 0.6353 g Ag2


I'm not sure if I'm on the right track here?
 

Answers and Replies

  • #2
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You have a system of two equations in two unknowns.
 

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