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Free Chemistry practice questions
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A galvanic cell is constructed from a zinc half-cell and a copper half-cell connected by a salt bridge. Using standard half-cell reduction potentials (Zn2+/Zn = -0.76 V; Cu2+/Cu = +0.34 V), write the overall cell equation, identify the anode, and calculate the cell's maximum EMF.
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1 mark: overall equation Zn(s) + Cu2+(aq) -> Zn2+(aq) + Cu(s). 1 mark: zinc electrode is the anode (oxidation, more negative reduction potential). 1 mark: correct method, EMF = E(cathode) - E(anode) = +0.34 - (-0.76). 1 mark: EMF = +1.10 V (must include the positive sign and unit V). Deduct the final mark if the value is correct but unsigned or unitless.
An electrolytic cell is used to electroplate a spoon with silver from a silver nitrate solution, passing a current of 2.50 A for 30.0 minutes. Calculate the mass of silver deposited. (F = 96500 C/mol; M(Ag) = 107.9 g/mol; Ag+ + e- -> Ag.)
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1 mark: Q = I x t = 2.50 x (30.0 x 60) = 4500 C. 1 mark: n(e-) = Q/F = 4500/96500 = 0.04663 mol. 1 mark: n(Ag) = n(e-) = 0.04663 mol (1:1 from the half-equation). 1 mark: m(Ag) = n x M = 0.04663 x 107.9 = 5.03 g (accept 5.0 to 5.03 g, must include unit g).
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