Question 19.4: Interpreting the Shorthand Notation for a Galvanic Cell Give...
Interpreting the Shorthand Notation for a Galvanic Cell
Given the following shorthand notation
Pt(s) \mid Sn^{2+}(aq), Sn^{4+}(aq) \parallel Ag^{+}(aq) \mid Ag(s)
write a balanced equation for the cell reaction, and give a brief description of the cell.
STRATEGY
We can obtain the cell half-reactions simply by reading the shorthand notation. To find the balanced equation for the cell reaction, add the two half-reactions after multiplying each by an appropriate factor so that the electrons will cancel. The shorthand notation specifies the anode on the left, the cathode on the right, and the reactants in the half-cell compartments.
Because the anode always appears at the left in the shorthand notation, the anode (oxidation) half-reaction is
Sn^{2+}(aq) → Sn^{4+}(aq) + 2 e^{-}
The platinum electrode is inert and serves only to conduct electrons. The cathode (reduction) half-reaction is
2 × [Ag^{+}(aq) + e^{-} → Ag(s)]
The cathode half-reaction is multiplied by a factor of 2 so that the electrons will cancel when the two half-reactions are summed to give the cell reaction:
Sn^{2+}(aq) + 2 Ag^{+}(aq) → Sn^{4+}(aq) + 2 Ag(s)
The cell consists of a platinum wire anode dipping into an Sn^{2+} solution—say, Sn(NO_{3})_{2}(aq)—and a silver cathode dipping into an Ag^{+} solution—say, AgNO_{3}(aq). As usual, the anode and cathode half-cells must be connected by a wire and a salt bridge containing inert ions.