posted by Anonymous .
An amount of 1.250g of an alloy (90% Ag, 10% Cu) was treated with HNO3 and H2SO4 to form Ag2SO4 and CuSO4. The solution was then treated with Cu wire to precipitate silver. The resulting solution was treated with excess zinc to precipitate copper. (show formula)
a). What mass of copper will be precipitated?
b). what total mass of zinc will be dissolved (neglect any dissolved by excess H2SO4)? Avoid any unnecessary steps in solving this problem.
1.250g x 0.90 = ??g Ag
1.250 x 0.10 = ??g Cu
Ag| + HNO3 ==> Ag2SO4
Cu| + HNO3 ==> CuSO4
2Ag^+ + Cu(s)(wire) = Ag(s) + Cu^+2(aq)
Then Zn(s) + Cu^+2(aq) ==> Zn^+2(aq) +
You know grams Ag initially. Convert to moles and use stoichiometry to calculate the amount of Cu(II) added to the solution when Ag was pptd. Here is a stoichiometry problem if you need it to get started.
Then Cu initially + Cu added to ppt Ag, gives moles Cu reacting with Zn.
Stoichiometry will give you the moles of Zn which can be converted to grams Zn.
In addition to neglecting H2SO4 we must also assume there is no excess of HNO3.