•A minus sign can be assigned to the anode in a voltaic cell, and the cathode is marked with a positive sign.•The chemical oxidation occurring at the anode, which produces electrons, gives it a negative charge. Electric current in the external circuit of a voltaic cell consists of electrons moving from the negative to the positive electrode.•In all electrochemical cells, electrons flow in the external circuit from the anode to the cathode.•Not all half-reactions involve a metal as a reactant or product.•With the exception of carbon in the form of graphite, most nonmetals are unsuitable as electrode materials because they do not conduct electricity. •It is not possible to make an electrode from a gas, a liquid, or a solution. Ionic solids do not make satisfactory electrodes because the ions are locked tightly in a crystal lattice, and these materials do not conduct electricity.
AP Chemistry - Electrochemistry•In situations where reactants and products cannot serve as the electrode material, an inert electrodemust be used. Such electrodes are made of materials that conduct an electric current but that are neither oxidized nor reduced in the cell.•The hydrogen electrodeis particularly important in the field of electrochemistry because it is used as a reference in assigning cell voltages.•When using shorthand for simplifying cell descriptions, the anode and information with respect to the solution with which it is in contact are always written on the left. A single vertical line (|) indicates a phase boundary, and double vertical lines (||) indicate a salt bridge. For example:•Cu(s)|Cu2+(aq, 1.0 M)||Ag+(aq, 1.0 M)|Ag(s)Section 20.3•Cells being compact or robust are high priorities for most applications. In most situations, it is also important that the cell produce a constant voltage. •Attempting to draw a large current results in a drop in voltage because the current depends on how faster ions in solution migrate to the electrode. Ion concentrations near the electrode become depleted if current is drawn rapidly, resulting in a decline in voltage.•The amount of current that can be drawn from a voltaic cell depends on the quantity of reagents consumed. A voltaic cell must have a large mass of reactants to produce current over a prolonged period. •In addition, a voltaic cell that can be recharged is attractive. Recharging a cell means returning the reagents to their original sites in the cell.•Batteries can be classified as primary and secondary. •Primary batteriesuse redox reactions that cannot be returned to their original state by recharging, so when the reactants are consumed, the battery is “dead” and must be discarded.•Secondary batteriesare often called storage batteriesor rechargeable batteries. The reactions in these batteries can be reversed; thus, the batteries can be recharged.
AP Chemistry - Electrochemistry•If you buy an inexpensive flashlight battery or dry cell battery, it will probably be a modern version of a voltaic cell invented by George LeClanché in 1866. Zinc serves as