Without the salt bridge, the compartments would not remain electrically neutral and no significant current would flow. These added cations “replace” the silver ions that are removed from the solution as they were reduced to silver metal, keeping the beaker on the right electrically neutral. At the same time, the nitrate ions are moving to the left, sodium ions (cations) move to the right, through the porous plug, and into the silver nitrate solution on the right. This keeps the beaker on the left electrically neutral by neutralizing the charge on the copper(II) ions that are produced in the solution as the copper metal is oxidized. ![]() ![]() As electrons flow from left to right through the electrode and wire, nitrate ions (anions) pass through the porous plug on the left into the copper(II) nitrate solution. The salt bridge consists of a concentrated, nonreactive, electrolyte solution such as the sodium nitrate (NaNO 3) solution used in this example. The circuit is closed using a salt bridge, which transmits the current with moving ions. At this point, no current flows-that is, no significant movement of electrons through the wire occurs because the circuit is open. The half-cell on the right side of the figure consists of the silver electrode in a 1 M solution of silver nitrate (AgNO 3). The silver is undergoing reduction the silver electrode is referred to as the cathode. The anode is connected to a voltmeter with a wire and the other terminal of the voltmeter is connected to a silver electrode by a wire. The copper is undergoing oxidation the copper electrode is referred to as the anode. The beaker on the left side of the figure is called a half-cell, and contains a 1 M solution of copper(II) nitrate with a piece of copper metal partially submerged in the solution. Galvanic or voltaic cells involve spontaneous electrochemical reactions in which the half-reactions are separated ( Figure 17.4) so that current can flow through an external wire. (credit: modification of work by Mark Ott) As the reaction proceeds (b), the solution turns blue (c) because of the copper ions present, and silver metal is deposited on the copper strip as the silver ions are removed from solution. The salt bridge is represented by a double line, ‖.Figure 17.3 When a clean piece of copper metal is placed into a clear solution of silver nitrate (a), an oxidation-reduction reaction occurs that results in the exchange of Cu 2+ for Ag + ions in solution. In this notation, information about the reaction at the anode appears on the left and information about the reaction at the cathode on the right. Electrochemical cells can be described using cell notation. The movement of these ions completes the circuit and keeps each half-cell electrically neutral. Anions in the salt bridge flow toward the anode and cations in the salt bridge flow toward the cathode. Adding a salt bridge completes the circuit allowing current to flow. The anode is connected to the cathode in the other half-cell, often shown on the right side in a figure. ![]() One half-cell, normally depicted on the left side in a figure, contains the anode. The half-cells separate the oxidation half-reaction from the reduction half-reaction and make it possible for current to flow through an external wire. These observations are consistent with (i) the oxidation of elemental copper to yield copper(II) ions, \ce(s) Check Your LearningĮlectrochemical cells typically consist of two half-cells. A copper wire and an aqueous solution of silver nitrate (left) are brought into contact (center) and a spontaneous transfer of electrons occurs, creating blue Cu2+(aq) and gray Ag(s) (right). A gradual but visually impressive change spontaneously occurs as the initially colorless solution becomes increasingly blue, and the initially smooth copper wire becomes covered with a porous gray solid.įigure 17.2.1. ![]() Use cell notation to symbolize the composition and construction of galvanic cellsĪs demonstration of spontaneous chemical change, Figure 17.2.1 shows the result of immersing a coiled wire of copper into an aqueous solution of silver nitrate.Describe the function of a galvanic cell and its components.
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