Voltaic cells standard electrode potentials

We can develop a series of standard electrode potentials by measuring the potentials of other standard electrodes versus the SHE in the way we described for the standard Zn-SHE and standard Cu-SHE voltaic cells. Many electrodes involve metals or nonmetals in contact with their ions. We saw (Section 21-12) that the standard Zn electrode behaves as the anode versus the SHE and that the standard oxidation potential for the Zn half-cell is 0.763 volt. 

Thus standard electrode potential (oxidation) of zinc electrode is 0.763 volts. This means that for the voltaic cell,... 

We can generalize this result for any voltaic cell the standard cell potential is the difference between the standard electrode potential of the cathode (reduction) half-cell and the standard electrode potential of the anode (oxidation) half-cell ... 

Now we can construct a voltaic cell consisting of this reference half-cell and another half-cell whose potential we want to determine. With E eference defined as zero, the overall Eceii allows us to find the unknown standard electrode potential. 

By combining many pairs of half-cells into voltaic cells, we can create a list of reduction half-reactions and arrange them in decreasing order of standard electrode potential (from most positive to most negative). Such a list, called an emf series or a table of standard electrode potentials, appears in Appendix D, with a few examples in Table 21.2 on the next page. 

Relating standard cell potential to standard electrode potentials in a voltaic cell (693) ... 

Based on the standard reduction potentials given above, if a silver electrode and a chromium electrode are connected in a voltaic cell, which electrode will undergo oxidation and which will undergo reduction Explain how you can tell. 

Students learn to use standard electrode potentials to predict cell voltage and spontaneity in voltaic cells. 

Finding for a Concentration Cell Suppose a voltaic cell has the Cu/Cu2+ halfreaction in both compartments. The cell reaction is the sum of identical half-reactions, written in opposite directions. The standard cell potential, , is zero because the standard electrode potentials are both based on 1 M Cu ", so they cancel. In a concentration cell, however, the concentrations are different. Thus, even though is still zero, the nonstandard cell potential, Sceii depends on the ratio of concentrations, so it is not zero. 

Calculate the standard emf of the following voltaic cell at 25°C nsing standard electrode potentials. 

The electromotive force (emf), or cell potential, is the maximum voltage of a voltaic cell. It can be directly related to the maximum work that can be done by the cell. A standard electrode potential, or reduction potential, refers to the potential of an electrode in which molar concentrations and gas pressures (in atmospheres) have unit values. A table of standard electrode potentials is useful for establishing the direction of spontaneity of an oxidation-reduction reaction and for calculating the standard emf of a cell. 

Calculating the emf from standard potentials Given standard electrode potentials, calculate the standard emf of a voltaic cell. (EXAMPLE 20.8)... 

Given standard electrode potentials and the concentrations of substances in a voltaic cell, calculate the cell emf. (EXAMPLE 20.12)... 

Table 9.8 summarizes some experimental results from a number of voltaic cells operating under standard conditions. These cell potentials can also be calculated from standard electrode potentials (Chapter 19). 

Thus, if the standard half-cell is connected to a standard hydrogen electrode to form a voltaic or electrochemical cell, the measured voltage, called the electromotive force (EMF), is the standard electrode potential of that half-cell. 

A voltaic cell is made from a Co (aq)/Co(s) halfcell and a Cu (aq)/Cu(s) half-cell. The cell potential was +0.62 V, with the copper half-cell positive. Calculate the standard electrode potential of the cobalt half-cell. 

A slightly different, but equivalent, approach to determining the cell potential of a voltaic cell involves subtracting the standard electrode potentials ... 

The standard electrode potential of a half-cell is not changed if the stoichiometry is changed. The voltage is a measure of the energy of an electron. Current is a measure of the number of electrons that flow past a point. The voltage of a simple voltaic cell does not depend on the amounts of chemicals used. 

To determine the value of E° for a sfandard electrode such as that to which half-cell reaction (19.6) applies, we compare it with a standard hydrogen electrode (SHE). In this comparison, the SHE is always taken as the electrode on the left of the cell diagram—the anode—and the compared electrode is the electrode on the right—the cathode. In the following voltaic cell, the measured potential difference is 0.340 V, wifh electrons flowing from the H2 to the Cu electrode. 

Cadmium is found in small quantities wherever zinc is foimd. Unlike zinc, which in trace amounts is an essential element, cadmium is an environmental poison. To determine cadmium ion concentrations by electrical measurements, we need the standard electrode potential for the Cd /Cd electrode. The voltage of the following voltaic cell is measured. 

When we combine standard electrode potentials, we obtain a standard Eceii/ such as Ecdi = 1.103 V for the voltaic cell of Figure 19-4. For the following cell reaction at nonstandard conditions, however, the measured Eceii is not 1.103 V. 

The voltaic cell in Figure 19-11 is called a concentration cell. A concentration cell consists of two half-cells with identical electrodes but different ion concentrations. Because the electrodes are identical, the standard electrode potentials are numerically equal and subtracting one from the other leads to the value E°eii = 0. However, because the ion concentrations differ, there is a potential... 

Zn (aq) + H20(l) + NO(g), describe the voltaic cell in which it occurs, label the anode and cathode, use a table of standard electrode potentials to evaluate eii / and balance the equation for the cell reaction. 

In a similar though less diabolical manner, the electrons produced at the anode of a voltaic cell have a natural tendency to flow along the circuit to a location with lower potential the cathode. This potential difference between the two electrodes causes the electromotive force, or EMF, of the cell. EMF is also often referred to as the cell potential and is denoted fj.g,. The cell potential varies with temperature and concentration of products and reactants and is measured in volts (V). The standard cell potential, or E° gn, is the that occurs when concentrations of solutions ire all at 1 M and the cell is at standard temperature and pressure (STP). 

A concentration cell is any voltaic cell in which two half-cells consist of identical electrodes with different solution concentrations. For such a cell, its cell potential under standard conditions, 8°g j, is zero. 

A voltaic cell contains one half-cell with a zinc electrode in a Zn2+ (aq) solution and a copper electrode in a Cu2+(aq) solution. At standard condition, E° = 1.10 V. Which condition below would cause the cell potential to be greater than 1.10 V ... 

Over the years, chemists have measured and recorded the standard reduction potentials, abbreviated of many different half-cells. Table 21-1 lists some common half-cell reactions in order of increasing reduction potential. The values in the table are based on using the half-cell reaction that is being measured as the cathode and the standard hydrogen electrode as the anode. All of the half-reactions in Table 21-1 are written as reductions. However, in any voltaic cell, which always contains two halfreactions, the half-reaction with the lower reduction potential will proceed in the opposite direction and will be an oxidation reaction. In other words, the half-reaction that is more positive will proceed as a reduction and the half-reaction that is more negative will proceed as an oxidation. 

A voltaic cell containing a standard Fe /Fe electrode and a standard Ga /Ga electrode is constructed, and the circuit is closed. Without consulting the table of standard reduction potentials, diagram and completely describe the cell from the following experimental observations, (i) The mass of the gallium electrode decreases, and the gallium ion concentration increases around that elec-... 

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