Method: identify elements being oxidized and reduced. Write oxidation and reductions reactions as half reactions. Cancel water present as reactants and products: check your answer for atom and charge balance. Galvanic (voltaic) cells: results from spontaneous chemical reactions. Electrolytic cell: uses electricity to accomplish non-spontaneous chemical change. Standard electrode potentials: absolute half-cell potentials cannot be measured, all potentials are measured relative to the standard hydrogen electrode (she); assigned a potential of 0v. E cell = voltage of a cell formed from 2 standard electrodes: for 2 half reactions combined in an electrochemical cell, the one with the more positive e value will proceed towards the right hand side (the reduction. E cell = e (cathode (right)) - e (anode (left)) It does not depend on the amount of substance reacting. Therefore, coefficients of half reactions are not considered when determining e . Spontaneity: e cell and g : electromotive force or cell potential (ecell)
Here, Zn undergoes oxidation by losing 2eâ, and the Cu2+ ions accept 2eâ to form metallic Cu, which is deposited at the copper electrode. At the zinc electrode, oxidation occurs, and hence it is known as the anode. Reduction occurs at the copper electrode, and hence it is called the cathode.
The electrochemical cell notation for this cell is Zn(s)|Zn2+(aq)||Cu2+(aq)|Cu(s).
Construction of a voltaic cell
Consider a chromium-silver voltaic cell that is constructed such that one half-cell consists of the chromium, Cr, electrode immersed in a Cr(NO3)3 solution, and the other half-cell consists of the silver, Ag, electrode immersed in a AgNO3 solution. The two electrodes are connected by a copper wire. The Cr electrode acts as the anode, and the Ag electrode acts as the cathode. To maintain electric neutrality, you add a KNO3 salt bridge separating the two half-cells. Use this information to solve Parts B, C, and D.
Part B
The half-cell is a chamber in the voltaic cell where one half-cell is the site of the oxidation reaction and the other half-cell is the site of the reduction reaction.
Type the half-cell reaction that takes place at the anode for the chromium-silver voltaic cell. Indicate the physical states using the abbreviation (s), (l), or (g) for solid, liquid, or gas, respectively. Use (aq) for an aqueous solution. Do not forget to add electrons in your reaction.
Express your answer as a chemical equation.
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Part C
The half-cell is a chamber in the voltaic cell where one half-cell is the site of an oxidation reaction and the other half-cell is the site of a reduction reaction.
Type the half-cell reaction that takes place at the cathode for the chromium-silver voltaic cell. Indicate physical states using the abbreviation (s), (l), or (g) for solid, liquid, or gas, respectively. Use (aq) for an aqueous solution. Do not forget to add electrons in your reaction.
