Operation of an Electrolytic Cell

Therefore, the reverse cell reaction is nonspontaneous and never happens of its own accord, as the negative gn and positive AG° indicate  

Note that in an electrolytic cell, as in a voltaic cell, oxidation takes place at the anode and reduction takes place at the cathode, but the direction of electron flow and the signs of the electrodes are reversed. 

To understand these changes, keep in mind the cause of the electron flow  

Cell Type AG cell Name Electrode Process Sign 

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Let s examine the operation of an electrolytic cell by constructing one from a voltaie eell. Consider the tin-copper voltaic cell in Figure 21.23A. The Sn anode... 

Let s examine the operation of an electrolytic cell by constructing one from a voltaic cell. Consider the tin-copper voltaic cell in Figure 21.23A. The Sn anode will gradually become oxidized to Sn ions, and the Cu " " ions will gradually be reduced and plate out on the Cu cathode because the cell reaction is spontaneous in that direction ... 

The operation of an electrolytic cell is described in Section 9.1. An electrolyte must contain charged ions for the cell to conduct a current when it is connected to an outside source of electricity. 

The information you have just learned permits a very precise control of electrolysis. For example, suppose you modify a Daniell cell to operate as an electrolytic cell. You want to plate 0.1 mol of zinc onto the zinc electrode. The coefficients in the half-reaction for the reduction represent stoichiometric relationships. Figure 11.23 shows that two moles of electrons are needed for each mole of zinc deposited. Therefore, to deposit 0.1 mol of zinc, you need to use 0.2 mol of electrons. 

It must be recognized that Fig. 11.1 is only a highly simplified representation of an electrolytic cell. Actual commercial practice usually employs a connected series of such cells constructed in a manner to meet the needs of each specific operation. Frequently, the vessel containing the electrolyte is made of metal and serves as one of the electrodes. Other modifications are shown in connection with commercial applications of electrolysis. 

The design of an electrolytic cell for batchwise operation in the laboratory normally does not present any problems. Many different types of cells of more or... 

Each mole of electrons that passes through the cell arises from the oxidation of j mol of Zn(s) (because each Zn atom gives up two electrons) and reduces 1 mol of silver ions. From the molar masses of silver and zinc, we calculate that 65.38/2 = 32.69 g of zinc is dissolved at the anode and 107.87 g of silver is deposited at the cathode. The same relationships hold if the cell is operated as an electrolytic cell, but in that case silver is dissolved and zinc is deposited. 

During the operation of an electrolysis cell, i.e., a cell driven by the application of an external voltage, the positive electrode sustains an oxidation (or anodic ) reaction with the liberation of electrons, while a reduction (or cathodic ) reaction takes place at the negative electrode with the uptake of electrons [Figure 4.1(a)]. For this reason, the positive electrode is often known as the anode and the negative electrode as the cathode . The internal circuit between the two electrodes is provided by the electrolyte, in which negative ions ( anions ) move towards the positive electrode and positive ions ( cations ) move towards the negative electrode. 

The cell in Figure 22-2 is a galvanic cell wilh a po-icntial of about 0,46 V, This cell is also chemically reversible and can be operated as an electrolytic cell b apphing an external potential of somewhat grcaiei... 

A schematic diagram of an electrolytic cell for producing aluminum by the Hall-Heroult process. Because molten aluminum is more dense than the mixture of molten cryolite and alumina, it settles to the bottom of the cell and is drawn off periodically. The graphite electrodes are gradually eaten away and must be replaced from time to time. The cell operates at a current flow of up to 250,000 A. 

As an example of an electrolytic cell, the text states Sodium chloride is electrolyzed commercially in an apparatus called the Downs cell to produce sodium and chlorine. This is a high-temperature operation the electrolyte is molten NaCl. Write the... 

Assume that the volume of each solution in Figure 19-22 is 100.0 mL. The cell is operated as an electrolytic cell, using a current of 0.500 A. Electrolysis is stopped after... 

Initially, each of the half-cells in Figure 19-21 contained a 100.0-mL sample of solution with an ion concentration of 1.000 M. The cell was operated as an electrolytic cell, with copper as the anode and zinc as the cathode. A current of 0.500 A was used. Assume that the only electrode reactions occurring were those involving Cu/Cu and Zn/Zn ". Electrolysis was stopped after 10.00 h, and the cell was allowed to function as a voltaic cell. What was Ecen at that point ... 

Anode impurities either dissolve in the electrolyte or fall to the bottom of the electrolytic cell as anode slime. These slimes contain silver, gold, selenium, and tellurium and represent a very significant value. Thus, the recovery of by-products from the anode slime is an important operation. 

An electrochemical cell is a device by means of which the enthalpy (or heat content) of a spontaneous chemical reaction is converted into electrical energy conversely, an electrolytic cell is a device in which electrical energy is used to bring about a chemical change with a consequent increase in the enthalpy of the system. Both types of cells are characterised by the fact that during their operation charge transfer takes place at one electrode in a direction that leads to the oxidation of either the electrode or of a species in solution, whilst the converse process of reduction occurs at the other electrode. 

If an electrolytic cell producingfluorineusesacurrentof7.00 X 103 A (at 10.0 V), how many grams of fluorine gas can be produced in two days (assuming that the cell operates continuously at 95% efficiency) ... 

Sulfur dioxide is soluble in the electrolyte. Sulfur is soluble up to about 1 mol dm 3, but it precipitates in the cathode pores near the end of discharge. Lithium chloride is essentially insoluble and precipitates on the surfaces of the pores of the carbon cathode, forming an insulating layer which terminates the operation of cathode-limited cells [37],... 

Aluminum is produced by electrolysis of its oxide dissolved in molten cryolite (Na AIFJ. Find the mass of aluminum that can be produced in 1.00 day (d) in an electrolytic cell operating continuously ai 1.00 X 105 A. The cryolite does nor react. 

Figure 6.18 Galvanic cell operationally differing from an electrolytic cell (two methods of representation are shown).

A galvanic cell operates of its own accord as a result of a spontaneous redox reaction. An electrolytic cell operates as a result of an external power source (e.g., a battery) in the circuit. 

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