A \"chemistry magic\" demonstration might involve dropping red-brown pieces of c

Question

A "chemistry magic" demonstration might involve dropping red-brown pieces of copper metal into a colorless silver nitrate solutions. The resulting reaction yields grains of silver metal in a blue-green solution. Balance this oxidation/reduction reaction. Express K in terms of concentrations. Calculate Delta G degree _rxn at 298 K. Calculate K at 298 K. Beginning with a pure silver nitrate solution of 0.155 M and adding copper until equilibrium is reached, what concentration of copper nitrate will be observed?

Explanation / Answer

a) Cu(s) + 2Ag+(aq) = Cu2+ (aq) + 2Ag(s) is balanced equation

b) K = [Cu2+]/ [Ag+]^2         ( solid and pure liquids have activity 1 )

c) Eo cell = Eo(Ag+/Ag) - Eo( Cu2+/Cu) = 0.8 - 0.34 = 0.46 V

dGo = -nFEo = - 2 x 96485 x 0.46 = - 88766 J/mol = - 88.766 KJ/mol

d) dGo = -RT ln K

-88766 = -8.314 x 298 ln K

K = 3.63 x 10^15

e) Since K is very high all Ag+ will be converted to Ag and all Cu(s) will be converted to Cu2+

[Ag+] =[AgNo3] = 0.155 as per balanced reaction [Cu2+ = 2 x [Ag+] = 2 x 0.155 = 0.31

hence concentartion of Cu2+ which is copper nitrate is 0.31 M

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