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. Cu(s) + Ag+ (aq) Cu^2+ + Ag (s) Balance this oxidation/reduction reaction. Express K in terms of concentrations. Calculate delta G0 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 + 2Ag+ = Cu2+ + 2Ag

b. K = [Cu2+]2 / [Ag+]  

c. Eocell = EoAg+/Ag – EoCu2+/Cu = 0.80 – 0.34 = 0.46 V

     dGo = -nFEocell =

            = - 2 x 96486 C x 0.46 V = -88.8 kJ

d.lnK = - dGo/(RT) = 88 767 J/mol / (8.314 J/mol.Kx298K) = 35.83

        K = e35.83 = 3.64x1015

e.

K is very high, so the reaction can be considered quite complete. According to the equation stoichiometry

[Cu2+]= 0.155 / 2 = 0.077 M

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