Voltaic cells half-cells

Zinc-copper voltaic cell. The cell has a potential of 1.1 volts when ZnS04 and CUSO4 solutions are 1.0 M. The salt bridge provides electrical contact between the two half-cells. 

It is convenient to have a shorthand way of designating particular voltaic cells. The cell described earlier, consisting of a zinc metal-zinc ion half-cell and a copper metal-copper ion half-cell, is written... 

To design a voltaic cell using the Zn-Cu2+ reaction as a source of electrical energy, the electron transfer must occur indirectly that is, the electrons given off by zinc atoms must be made to pass through an external electric circuit before they reduce Cu2+ ions to copper atoms. One way to do this is shown in Figure 18.2. The voltaic cell consists of two half-cells—... 

A Zn-Cu + voltaic cell. In this voltaic cell, a voltmeter (left) is connected to a half-cell consisting of a Cu cathode in a solution of blue Cu2+ ions and a half-cell consisting of a Zn anode in a solution of colorless Zn2+ ions. The following spontaneous reaction takes place in this cell Zn(s) + Ctf+lag) — M+(atfl + Cu(s). 

A voltaic cell using this reaction is similar to the Zn-Cu2+ cell the Zn Zn2+ half-cell and the salt bridge are the same. Because no metal is involved in the cathode half-reaction, an inert electrode that conducts an electric current is used. Frequently, the cathode is made of platinum (Figure 18.3, p. 484). In the cathode, Co3+ ions are provided by a solution of Co(N03)3. The half-reactions occurring in the cell are... 

A voltaic cell consists of two half-cells. One of the half-cells contains a platinum electrode surrounded by chromium(III) and dichromate ions. The other half-cell contains a platinum electrode surrounded by bromate ions and liquid bromine. Assume that the cell reaction, which produces a positive voltage, involves both chromium(III) and bromate ions. The cell is at 25°C. Information for the bromate reduction half reaction is as follows ... 

The reaction may be regarded as taking place in a voltaic cell, the two half-cells being a C12,2C1 system and a Fe3+,Fe2+ system. The reaction is allowed to proceed to equilibrium, and the total voltage or e.m.f. of the cell will then be zero, i.e. the potentials of the two electrodes will be equal ... 

The voltaic cell with the highest voltage will be the one connecting the K+/K half-cell with the F2/F half-cell E° ... 

In a concentration cell, we have 2 half cells containing the same ions and gases, only at different concentrations and/or partial pressures. Assume that the partial pressure of H2(g) in both cells is 1 atm. The spontaneous reaction occurring in the voltaic cell will proceed in the direction that will try to equalize the concentration of H+ ion. 

Galvanic (voltaic) cells produce electricity by using a redox reaction. Let s take that zinc/copper redox reaction that we studied before (the direct electron transfer one) and make it a galvanic cell by separating the oxidation and reduction half-reactions. 

A certain voltaic cell is composed of a Ce4+/Ce3+ half-cell and a Sn4+/Sn2+ half-cell. The overall cell reaction is... 

A half-cell describes a single electrode and its associated chemical reaction which forms part of a voltaic cell. 

A voltaic cell converts chemical energy into electrical energy. It consists of two parts called half-cells. When two different metals, one in each half-cell, are used in the voltaic cell, a potential difference is produced. In this experiment, you will measure the potential difference of various combinations of metals used in voltaic cells and compare these values to the values found in the standard reduction potentials table. 

Applying Concepts Write the half-reactions for the anode and cathode in each of the voltaic cells in the data table. Look up the half-reaction potentials from the standard reduction potentials table (Table 21-1) and record these in the data table. 

A voltaic cell is constructed using Al andAl+3 in one half cell andAg andAg+ in the other half-cell... 

This reaction takes place when zinc and copper cire in direct contact, but as we explain ecir-lier in this section, a voltaic cell is created by connecting the two reactants by an external pathway. Only the electrons created at the anode in the oxidation reaction can travel to the reduction half of the reaction along this external pathway. A voltaic cell using this Scime oxidation-reduction reaction between copper and zinc is shown in Figure 19-1, which we examine piece by piece. 

Table 19-1 lists some standcird reduction potentials along with the reduction half-reactions associated with them. The table is ordered from the most negative (most likely to oxidize) to the most positive E° (most likely to be reduced). The reactions with negative E° are therefore reactions that happen at the anode of a voltaic cell, while those with a positive... 

Note that not all the reactions in Table 19-1 show the reduction of solid metals, as in our examples so far. We ve thrown in liquids and gases as well. Not every voltaic cell is fueled by a reaction taking place between the metals of the electrodes. Although the cathode itself must be made of a metal to allow for the flow of electrons, those electrons can be passed into a gas or a liquid to complete the reduction half-reaction. Examine Figure 19-2 for an example of such a cell, which includes a gaseous electrode. 

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. 

Calculate the standard cell potentials (emf) in a voltaic cell whose half-reactions are given below. 

Of interest is the use of this system as both solvent and reactant in a voltaic cell. If two platinum gauze electrodes are immersed in liquid chlorocuprates and a potential is applied, the cell begins charging- At less than 1/of full charge, the potential stabilizes at 0.85 V and remains at that value until the cell is fully charged. The half-reactions for charging are... 

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 ... 

A voltaic cell (also known as a galvanic cell) is a device that allows for the transfer of electrons (in a redox reaction) to be completed in a separate pathway from the reaction mixtures. In a voltaic cell, the two half-reactions are physically separated from each other by placing them into two separate reaction vessels. The electrons are transferred from one vessel to the other by a connecting wire (see Figure 18.1). In voltaic cells, the reactions in each vessel must be spontaneous. In figure 18.1, in the reaction on the left, a zinc strip is placed in a zinc sulfate solution, where zinc from the strip replaces zinc in solution (Zn —> Zn2+ + 2 c ). In the reaction vessel on the left, the zinc strip will lose mass over time. Electrons create an electric potential difference across the wire, which is also known as a voltage. The voltage across the wire will allow electrons to be forced from the zinc strip, across the wire, to the copper strip. However, an electric current cannot be established until the circuit is completed. 

To summarize voltaic cells, let s review the components that create the cell. First, you need two half-cells, each of which contains an electrode immersed in an electrolytic solution (typically containing the cation of the metal in the electrode). A spontaneous reaction must occur between the electrode and the solution. A wire connects the two electrodes and will allow the external flow of electrons from the anode to the cathode. In Figure 18.1, a voltmeter is shown as part of the circuit between the two electrodes. This is not a necessary part of the circuit—it is simply there to measure the voltage across the circuit. The salt bridge completes the electric circuit and allows the flow of cations and anions between the two half-reactions. Sometimes a porous disc is used in place of a salt bridge. The driving force for the current is the difference in potential energies between the two half-cells. 

You have probably worked with tables of standard reduction potentials before. These tables provide the reduction potentials of various substances. It describes an oxidized species s ability to gain electrons in a reduction half-reaction (like copper in the voltaic cell example). According to this definition, we can use a value from the table to represent the E°red in the expression above, but how do you find the E°ox ... 

Sample A voltaic cell is created with two half-cells. In the first half-cell, a copper electrode is placed in a 1.0 M Cu(N03)2 solution. In the second half-cell, a tin electrode is placed in a solution of 1.0 M Sn(N03)2. A salt bridge is placed between the two half-cells to complete the circuit. Assume tin is the anode. Calculate the cell voltage of the voltaic cell. 

An electrolytic cell is similar to a voltaic cell, but there are some slight differences. One of the first differences is the source of electrons. In the voltaic cell, the source of the electrons is the spontaneous oxidation that occurs at the anode. Because no spontaneous reactions occur in an electrolytic cell, the source of electrons is a DC (direct current) power supply. The power supply forces electrons to the cathode rather than the potential of the half-reactions. The cathode in an electrolytic cell acquires a negative charge (which is opposite from a voltaic cell) because electrons are being forced onto it, while the anode takes on a positive charge (which is opposite from a voltaic cell) because electrons are being removed from it by the power supply. 

In the section on voltaic cells, we saw that the anode lost mass over time (as the metals were oxidized and went into solution), while the cathode gained mass over time (as the cations were reduced and plated on the surface). The voltaic cell, however, requires spontaneous reactions in each half-cell, which limits the types of electrodes that can be used. In an electrolytic cell, because we are adding electric current to the cathode and the anode, we can force nonspontaneous reactions to occur. In some cases, this allows us to use electrolysis for purposes other than separating a molten compound or aqueous solution. One of the more common alternate uses is the purification of different metals. 

A voltaic cell is created with one half-cell consisting of a copper electrode immersed in 1.0 M CuS04 solution and the other half-cell consisting of a lead electrode immersed in a 1.0 M Pb(N03)2 solution. Each half-cell is maintained at 25°C. What is the cell potential, in volts ... 

A voltaic cell is set up with two half-cells. In the first half-cell, a silver electrode is placed in an aqueous solution containing... 

A voltaic, or galvanic, cell allows the oxidation and reduction of substances to be physically separated. This is accomplished by allowing the electrons to pass from one location to the other by way of an external path (such as a wire). The circuit in a voltaic cell must be completed using a salt bridge or another porous barrier that allows for the transfer of anions between the two half-cells. 

Voltaic cells can only be created when each half-cell contains a reaction that occurs spontaneously. Because of this, cell voltage and free energy can be related (using Equation 18.3). 

In a voltaic cell, one half-cell contains a cobalt electrode immersed in a... 

The correct answer is (A). The anode in a galvanic (voltaic) cell is where oxidation occurs. Choice (A) is the only example of an oxidation that could occur in a half-cell (Zinc is losing electrons). 

The wire in the voltaic cell carries the electrons from one half cell to another. The salt bridge allows ions to migrate from one half cell to the other so that there is no buildup of charge as the electrons are transferred from one half cell to the other. The electrodes are the sites of oxidation and reduction in the voltaic cell. These processes will occur on the surfaces of the cathode (electrode where reduction occurs) and the anode (electrode where oxidation occurs). 

Look back at Figure 10.1 showing the Zn and Cu electrodes set up in the voltaic cell. For simplicity, the setup can be abbreviated by writing Zn / Zn2+ // Cu / Cu2+. The electrons will flow spontaneously from the Zn electrode to the Cu electrode because according to the activity series, Zn is a more active metal than Cu. This means that Zn behaves more like a metal and loses electrons easily. The half reaction for Zn in this half cell will be Zn — Zn2+ + 2e. ... 

PROBLEM For the voltaic cell Al / Al3+// Co / Co2+, write the two half reactions and determine which electrode is the anode and which is the cathode. 

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