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Chapter 18
Electrochemistry
18.1
Title
 Displacement of Ag+(aq) by Cu(s)
Caption
 Displacement of Ag+(aq) by Cu(s) in this oxidation-reduction reaction results in the formation of Cu2+ ions as the electrons are transferred to Ag+(aq) to make Ag(s).
Keywords
 redox, oxidation, reduction, oxidizing agent, reducing agent
18.3b
Title
 Electrode equilibrium
Caption
 The zinc metal strip, called an electrode, is partially immersed in a solution containing Zn2+ ions. Oxidation of Zn to Zn2+ (near the bottom of the microscopic view) and the reduction of Zn2+ to Zn (near top) occur at the elctrode until a condition of equilibrium is reached. For clarity, the anions needed to produce an electrically neutral solution are not shown.
Keywords
 electrode, oxidation, reduction, equilibrium
18.4
Title
 A Zinc-Copper voltaic cell
Caption
 Zinc atoms lose electrons and enter the solution as Zn2+ ions (red arrow). Electrons flow through the external circuit from the Zn to the Cu electrode. At the copper electrode, Cu2+ ions gain electrons and deposit as Cu atoms (blue arrow). Ion migrations through the solutions are noted by the black arrows. Porous plugs prevent the bulk flow of solution but permit the ions to migrate through the salt bridge. The voltmeter reading is discussed on page 775. Voltaic cells similar to these (Daniell cells) were used to power telegraph lines in the early days of the telegraph.
Keywords
 voltaic cell, oxidation, reduction, redox, electricity, current, salt bridge
18.4.1
Title
 Electrochemical cell diagram
Caption
 By convention, electrochemical cells are written in the form: Anode-Salt bridge-Cathode, with the detail shown here.
Keywords
 half cell, electrochemical cell, anode, cathode, reduction, oxidation
18.5
Title
 Standard hydrogen electrode
Caption
 The inert platinum strip acquires a potential that is determined by the equilibrium: 2 H+(aÊ=Ê1)Ê+Ê2 e- <-->H2(g, 1 atm). The condition of aH+=1 can be approximated by [H+]Ê=Ê1 M and that of 1 bar by 1atm.
Keywords
 electrode, reduction potential, standard hydrogen electrode, oxidation, reduction, activity
18.6
Title
 Measuring the potential of the Cu2+/Cu electrode
Caption
 The standard hydrogen electrode is the anode and the Cu2+/Cu electrode is the cathode. Contact between the solutions in the two half-cells is through a porous plate, which permits the migration of ions but prevents bulk flow of the solutions. The direction of electron flow and the voltmeter reading are shown.
Keywords
 reduction, oxidation, current, volts, standard hydrogen electrode, reduction potential
18.7
Title
 Measuring the standard potential of the Zn2+/Zn electrode
Caption
 As in Figure 18.6, the standard hydrogen electrode appears on the left and the metal electrode on the right. However, as signified by the direction of electron flow and the negative voltage, the standard hydrogen electrode is the cathode. The Zn2+/Zn electrode is the anode. When voltaic cells are assembled as in Figures 18.6 and 18.7, correct magnitudes and signs of all standard electrode potentials can be established.
Keywords
 electrode, reduction, oxidation, anode, cathode, electrochemical cell, standard reduction potential
18.11
Title
 Summary of important relationships from thermodynamics, equilibrium, & electrochemistry
Caption
 The three thermodynamic quantities Keq, Go, and Eo for a chemical reaction are related on a theoretical basis and are mathematically related as shown. Other properties of the reactions (e.g., DHo and DSo) in effect determine each of the other quantities, and vice versa. It is possible, as shown, to use calorimetry data from an experiment to determine all the other quantities shown.
Keywords
 thermodynamics, equillibrium, free energy, enthalpy, reduction potential, entropy
18.12
Title
 Determining the expected voltmeter reading for voltaic cell
Caption
 In determining the expected voltmeter reading for voltaic cell (text exercise 18.9) requires use of the Nernst equation and the standarde reduction potentials. The Eo =+0.431V. Taking concentration into account, the E for this cell is +0.458V.
Keywords
 example, electrochemical cell, Nernst equation, reduction potential
18.13
Title
 A concentration cell
Caption
 In a concentration cell, the electrodes are identical, but the solution concentrations differ. The driving force for the cell reaction is the tendency for the solution concentrations to become equalized: Cu2+(1.50 M)Ê-->Cu2+(0.025 M).
Keywords
 electrochemical cell, concentration gradient, concentration cell, reduction potential, Nernst equation, electrochemistry, redox
18.13.1
Title
 Model of a portion of a cell membrane w/K+ channel & Na+ channel
Caption
 This computer-generated model of a portion of a cell membrane shows a K+ channel (blue) and a Na+ channel (red). The area outside the cell (top) is rich in Na+ and low in K+. Inside the cell, the fluids are relatively rich in K+ and low in Na+.
Keywords
 membrane, ion, gradient, electrochemical potential, channel
18.15
Title
 Cross-section of a Leclanche (dry) cell
Caption
 The moist paste consists of NH4Cl(aq) and ZnCl2(aq); carbon black (a finely divided form of carbon) and MnO2(s) are also present.
Keywords
 battery, dry cell, anode, redox, cathode, oxidation, reduction, electrochemical potential
18.16
Title
 A lead-acid (storage) cell
Caption
 The composition of the electrodes, the cell reaction, and the cell voltage are described in the text. Shown here are two anode plates and two cathode plates in parallel connections. This type of connection increases the surface area of the electrodes and the capacity of the cell to deliver current.
Keywords
 battery, redox, electrochemical cell, anode, cathode
18.17
Title
 A hydrogen-oxygen fuel cell
Caption
 The electrodes are porous to allow easy access of the gaseous reactants to the electrolyte. The electrode material also catalyzes the electrode reactions.
Keywords
 fuel, redox, anode, cathode, reduction potential, electrochemical cell, voltaic cell
18.18
Title
 Corrosion of an iron piling: an electrochemical process
Caption
 This schematic drawing illustrates the anodic and cathodic regions, their half-reactions, and the final formation of rust. The cathodic region is near the air-water interface, where the availability of O2(g) is greatest. The anodic region is at greater depths below the waterÕs surface. Fe2+(aq) from the anodic region migrates to the cathodic region, where rust formation occurs.
Keywords
 rust, andode, cathode, voltaic cell, electrochemical cell, oxidation, reduction
18.20
Title
 Electrolysis of molten sodium chloride
Caption
 The electrolysis cell pictured here is called a Downs cell. The electrolyte is molten NaCl with a small amount of CaCl2 added to lower its melting point. Liquid sodium forms at the steel cathode and gaseous chlorine at the graphite anode. A steel gauze diaphragm keeps the sodium and chlorine from recombining to form sodium chloride.
Keywords
 electrolysis, cathode, anode, spontenatity, electrochemical cell, reduction potential
18.21
Title
 A diaphragm chlor-alkali cell
Caption
 The anode is a specially treated titanium metal. The diaphragm and cathode are a composite unit consisting of an asbestos-polymer mixture deposited on a steel wire mesh. A difference in the solution levels is maintained, so that NaCl(aq) moves through the diaphragm during the electrolysis.
Keywords
 redox, electrochemical cell, electrolysis
18.22
Title
 Electrochemical cell for silver plating
Caption
 The anode is a silver bar, and the cathode is an iron spoon.
Keywords
 silver plating, electrochemical cell, redox, oxidation, reduction, oxidizing agent, reducing agent, cathode, anode
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