The half-cell, called the anode, is the site at which the oxidation of zinc occurs as shown below.
Zn (s) ----------> Zn+2 (aq) + 2e-
During the oxidation of zinc, the zinc electrode will slowly dissolve to produce zinc ions (Zn+2), which enter into the solution containing Zn+2 (aq) and SO4-2 (aq) ions.
The half-cell, called the cathode, is the site at which reduction of copper occurs as shown below.
Cu+2 (aq) + 2e- -------> Cu (s)
When the reduction of copper ions (Cu+2) occurs, copper atoms accumulate on the surface of the solid copper electrode.
The reaction in each half-cell does not occur unless the two half cells are connected to each other.
Recall that in order for oxidation to occur, there must be a corresponding reduction reaction that is linked or "coupled" with it. Moreover, in an isolated oxidation or reduction half-cell, an imbalance of electrical charge would occur, the anode would become more positive as zinc cations are produced, and the cathode would become more negative as copper cations are removed from solution. This problem can be solved by using a "salt bridge" connecting the two cells as shown in the diagram below. A "salt bridge" is a porous barrier which prevents the spontaneous mixing of the aqueous solutions in each compartment, but allows the migration of ions in both directions to maintain electrical neutrality. As the oxidation-reduction reaction occurs, cations ( Zn+2) from the anode migrate via the salt bridge to the cathode, while the anion, (SO4)-2, migrates in the opposite direction to maintain electrical neutrality.
The two half-cells are also connected externally. In this arrangement, electrons provided by the oxidation reaction are forced to travel via an external circuit to the site of the reduction reaction. The fact that the reaction occurs spontaneously once these half cells are connected indicates that there is a difference in potential energy. This difference in potential energy is called an electomotive force (emf) and is measured in terms of volts. The zinc/copper cell has an emf of about 1.1 volts under standard conditions.
The half-cell, called the anode, is the site at which the oxidation of zinc occurs as shown below.
Zn (s) ----------> Zn+2 (aq) + 2e-
During the oxidation of zinc, the zinc electrode will slowly dissolve to produce zinc ions (Zn+2), which enter into the solution containing Zn+2 (aq) and SO4-2 (aq) ions.
The half-cell, called the cathode, is the site at which reduction of copper occurs as shown below.
Cu+2 (aq) + 2e- -------> Cu (s)
When the reduction of copper ions (Cu+2) occurs, copper atoms accumulate on the surface of the solid copper electrode.
The reaction in each half-cell does not occur unless the two half cells are connected to each other.
Recall that in order for oxidation to occur, there must be a corresponding reduction reaction that is linked or "coupled" with it. Moreover, in an isolated oxidation or reduction half-cell, an imbalance of electrical charge would occur, the anode would become more positive as zinc cations are produced, and the cathode would become more negative as copper cations are removed from solution. This problem can be solved by using a "salt bridge" connecting the two cells as shown in the diagram below. A "salt bridge" is a porous barrier which prevents the spontaneous mixing of the aqueous solutions in each compartment, but allows the migration of ions in both directions to maintain electrical neutrality. As the oxidation-reduction reaction occurs, cations ( Zn+2) from the anode migrate via the salt bridge to the cathode, while the anion, (SO4)-2, migrates in the opposite direction to maintain electrical neutrality.
The two half-cells are also connected externally. In this arrangement, electrons provided by the oxidation reaction are forced to travel via an external circuit to the site of the reduction reaction. The fact that the reaction occurs spontaneously once these half cells are connected indicates that there is a difference in potential energy. This difference in potential energy is called an electomotive force (emf) and is measured in terms of volts. The zinc/copper cell has an emf of about 1.1 volts under standard conditions.
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