Solved: The blood alcohol (C2H5OH) level can be determined by titrating a sample of

Potassium dichromate (K2Cr2O7) is a bright orange compound that can be reduced to a blue-violet solution of Cr31 ions. Under certain conditions, K2Cr2O7 reacts with ethanol (C2H5OH) as follows: H1 1aq2 1 Cr2O7 22 1aq2 1 C2H5OH1l2 h Cr31 1aq2 1 CO2 1g2 1 H2O1l2 Balance this equation using the half-reaction method.

When balancing redox reactions occurring in basic solutions, the text instructs you to first use the half-reaction method as specified for acidic solutions. What if you started by adding OH2 first instead of H1? What potential problem could there be with this approach?

Silver is sometimes found in nature as large nuggets; more often it is found mixed with other metals and their ores. An aqueous solution containing cyanide ion is often used to extract the silver using the following reaction that occurs in basic solution: Ag1s2 1 CN2 1aq2 1 O2 1g2 hBase Ag1CN2 2 2 1aq2 Balance this equation using the half-reaction method.

What if you want to plate out copper metal from an aqueous Cu21 solution? Use Table 18.1 to determine several metals you can place in the solution to plate copper metal from the solution. Defend your choices. Why can Zn not be plated out from an aqueous solution of Zn21 using the choices in Table 18.1?

a. Consider a galvanic cell based on the reaction Al31 1aq2 1 Mg1s2 h Al1s2 1 Mg21 1aq2 The half-reactions are Al31 1 3e2 h Al % 5 21.66 V (1) Mg21 1 2e2 h Mg % 5 22.37 V (2) Give the balanced cell reaction, and calculate 8 for the cell. b. A galvanic cell is based on the reaction MnO4 2 1aq2 1 H1 1aq2 1 ClO3 2 1aq2 h ClO4 2 1aq2 1 Mn21 1aq2 1 H2O1l2 The half-reactions are MnO4 2 1 5e2 1 8H1 h Mn21 1 4H2O % 5 1.51 V (1) ClO4 2 1 2H1 1 2e2 h ClO3 2 1 H2O % 5 1.19 V (2) Give the balanced cell reaction, and calculate 8 for the cell.

Describe completely the galvanic cell based on the following half-reactions under standard conditions: Ag1 1 e2 h Ag % 5 0.80 V (1) Fe31 1 e2 h Fe21 % 5 0.77 V (2)

Using the data in Table 18.1, calculate DG8 for the reaction Cu21 1aq2 1 Fe1s2 h Cu1s2 1 Fe21 1aq2 Is this reaction spontaneous?

Using the data from Table 18.1, predict whether 1 M HNO3 will dissolve gold metal to form a 1-M Au31 solution.

For the cell reaction 2Al1s2 1 3Mn21 1aq2 h 2Al31 1aq2 1 3Mn1s2 % cell 5 0.48 V predict whether cell is larger or smaller than 8 cell for the following cases. a. [Al31] 5 2.0 M, [Mn21] 5 1.0 M b. [Al31] 5 1.0 M, [Mn21] 5 3.0 M

Determine the direction of electron flow, and designate the anode and cathode for the cell represented in Fig. 18.10.

What if you are told that 8 5 0 for an electrolytic cell? Does this mean the cell is dead? What if 5 0? Explain your answer in each case.

Describe the cell based on the following half-reactions: VO2 1 1 2H1 1 e2 h VO21 1 H2O % 5 1.00 V (1) Zn21 1 2e2 h Zn % 5 20.76 V (2) where T 5 25C 3VO2 1 4 5 2.0 M 3H1 4 5 0.50 M 3VO21 4 5 1.0 3 1022 M 3Zn21 4 5 1.0 3 1021 M

For the oxidationreduction reaction S4O6 22 1aq2 1 Cr21 1aq2 h Cr31 1aq2 1 S2O3 22 1aq2 the appropriate half-reactions are S4O6 22 1 2e2 h 2S2O3 22 % 5 0.17 V (1) Cr31 1 e2 h Cr21 % 5 20.50 V (2) Balance the redox reaction, and calculate 8 and K (at 258C).

How long must a current of 5.00 A be applied to a solution of Ag1 to produce 10.5 g silver metal?

An acidic solution contains the ions Ce41, VO2 1, and Fe31. Using the 8 values listed in Table 18.1, give the order of oxidizing ability of these species, and predict which one will be reduced at the cathode of an electrolytic cell at the lowest voltage.

What is a half-reaction? Why must the number of electrons lost in the oxidation half-reaction equal the number of electrons gained in the reduction halfreaction? Summarize briefly the steps in the half-reaction method for balancing redox reactions. What two items must be balanced in a redox reaction (or any reaction)?

Galvanic cells harness spontaneous oxidationreduction reactions to produce work by producing a current. They do so by controlling the flow of electrons from the species oxidized to the species reduced. How is a galvanic cell designed? What is in the cathode compartment? The anode compartment? What purpose do electrodes serve? Which way do electrons always flow in the wire connecting the two electrodes in a galvanic cell? Why is it necessary to use a salt bridge or a porous disk in a galvanic cell? Which way do cations flow in the salt bridge? Which way do the anions flow? What is a cell potential and what is a volt?

Table 18.1 lists common half-reactions along with the standard reduction potential associated with each half-reaction. These standard reduction potentials are all relative to some standard. What is the standard (zero point)? If 8 is positive for a half-reaction, what does it mean? If 8 is negative for a half-reaction, what does it mean? Which species in Table 18.1 is most easily reduced? Least easily reduced? The reverse of the half-reactions in Table 18.1 are the oxidation halfreactions. How are standard oxidation potentials determined? In Table 18.1, which species is the best reducing agent? The worst reducing agent? To determine the standard cell potential for a redox reaction, the standard reduction potential is added to the standard oxidation potential. What must be true about this sum if the cell is to be spontaneous (produce a galvanic cell)? Standard reduction and oxidation potentials are intensive. What does this mean? Summarize how line notation is used to describe galvanic cells.

Consider the equation DG 5 2nF%. What are the four terms in this equation? Why does a minus sign appear in the equation? What does the superscript indicate?

The Nernst equation allows determination of the cell potential for a galvanic cell at nonstandard conditions. Write out the Nernst equation. What are nonstandard conditions? What do , 8, n, and Q stand for in the Nernst equation? What does the Nernst equation reduce to when a redox reaction is at equilibrium? What are the signs of DG and 8 when K , 1? When K . 1? When K 5 1? Explain the following statement: determines spontaneity, while 8 determines the equilibrium position. Under what conditions can you use 8 to predict spontaneity?

What are concentration cells? What is 8 in a concentration cell? What is the driving force for a concentration cell to produce a voltage? Is the higher or the lower ion concentration solution present at the anode? When the anode ion concentration is decreased and/or the cathode ion concentration is increased, both give rise to larger cell potentials. Why? Concentration cells are commonly used to calculate the value of equilibrium constants for various reactions. For example, the silver concentration cell illustrated in Fig. 18.9 can be used to determine the Ksp value for AgCl(s). To do so, NaCl is added to the anode compartment until no more precipitate forms. The [Cl2] in solution is then determined somehow. What happens to cell when NaCl is added to the anode compartment? To calculate the Ksp value, [Ag1] must be calculated. Given the value of cell, how is [Ag1] determined at the anode?

Batteries are galvanic cells. What happens to cell as a battery discharges? Does a battery represent a system at equilibrium? Explain. What is cell when a battery reaches equilibrium? How are batteries and fuel cells alike? How are they different? The U.S. space program utilizes hydrogenoxygen fuel cells to produce power for its spacecraft. What is a hydrogenoxygen fuel cell?

Not all spontaneous redox reactions produce wonderful results. Corrosion is an example of a spontaneous redox process that has negative effects. What happens in the corrosion of a metal such as iron? What must be present for the corrosion of iron to take place? How can moisture and salt increase the severity of corrosion? Explain how the following protect metals from corrosion: a. paint b. durable oxide coatings c. galvanizing d. sacrificial metal e. alloying f. cathodic protection

What characterizes an electrolytic cell? What is an ampere? When the current applied to an electrolytic cell is multiplied by the time in seconds, what quantity is determined? How is this quantity converted to moles of electrons required? How are moles of electrons required converted to moles of metal plated out? What does plating mean? How do you predict the cathode and the anode half-reactions in an electrolytic cell? Why is the electrolysis of molten salts much easier to predict in terms of what occurs at the anode and cathode than the electrolysis of aqueous dissolved salts? What is overvoltage?

Electrolysis has many important industrial applications. What are some of these applications? The electrolysis of molten NaCl is the major process by which sodium metal is produced. However, the electrolysis of aqueous NaCl does not produce sodium metal under normal circumstances. Why? What is purification of a metal by electrolysis?

Sketch a galvanic cell, and explain how it works. Look at Figs. 18.1 and 18.2. Explain what is occurring in each container and why the cell in Fig. 18.2 works but the one in Fig. 18.1 does not.

In making a specific galvanic cell, explain how one decides on the electrodes and the solutions to use in the cell.

You want to plate out nickel metal from a nickel nitrate solution onto a piece of metal inserted into the solution. Should you use copper or zinc? Explain

A copper penny can be dissolved in nitric acid but not in hydrochloric acid. Using reduction potentials from the book, show why this is so. What are the products of the reaction? Newer pennies contain a mixture of zinc and copper. What happens to the zinc in the penny when the coin is placed in nitric acid? Hydrochloric acid? Support your explanations with data from the book, and include balanced equations for all reactions.

Sketch a cell that forms iron metal from iron(II) while changing chromium metal to chromium(III). Calculate the voltage, show the electron flow, label the anode and cathode, and balance the overall cell equation

Which of the following is the best reducing agent: F2, H2, Na, Na1, F2? Explain. Order as many of these species as possible from the best to the worst oxidizing agent. Why cant you order all of them? From Table 18.1 choose the species that is the best oxidizing agent. Choose the best reducing agent. Explain

You are told that metal A is a better reducing agent than metal B. What, if anything, can be said about A1 and B1? Explain

Explain the following relationships: DG and w, cell potential and w, cell potential and DG, cell potential and Q. Using these relationships, explain how you could make a cell in which both electrodes are the same metal and both solutions contain the same compound, but at different concentrations. Why does such a cell run spontaneously?

Explain why cell potentials are not multiplied by the coefficients in the balanced redox equation. (Use the relationship between DG and cell potential to do this.)

What is the difference between and 8? When is equal to zero? When is 8 equal to zero? (Consider regular galvanic cells as well as concentration cells.)

Consider the following galvanic cell: Zn Ag 1.0 M Zn2+ 1.0 M Ag+ What happens to as the concentration of Zn21 is increased? As the concentration of Ag1 is increased? What happens to 8 in these cases?

Look up the reduction potential for Fe31 to Fe21. Look up the reduction potential for Fe21 to Fe. Finally, look up the reduction potential for Fe31 to Fe. You should notice that adding the reduction potentials for the first two does not give the potential for the third. Why not? Show how you can use the first two potentials to calculate the third potential.

If the cell potential is proportional to work and the standard reduction potential for the hydrogen ion is zero, does this mean that the reduction of the hydrogen ion requires no work?

Is the following statement true or false? Concentration cells work because standard reduction potentials are dependent on concentration. Explain.

Define oxidation and reduction in terms of both change in oxidation number and electron loss or gain.

Assign oxidation numbers to all the atoms in each of the following: a. HNO3 e. C6H12O6 i. Na2C2O4 b. CuCl2 f. Ag j. CO2 c. O2 g. PbSO4 k. (NH4)2Ce(SO4)3 d. H2O2 h. PbO2 l. Cr2O3

Specify which of the following equations represent oxidation reduction reactions, and indicate the oxidizing agent, the reducing agent, the species being oxidized, and the species being reduced. a. CH4 1g2 1 H2O1g2 S CO1g2 1 3H2 1g2 b. 2AgNO3 1aq2 1 Cu1s2 S Cu1NO32 2 1aq2 1 2Ag1s2 c. Zn1s2 1 2HCl1aq2 S ZnCl2 1aq2 1 H2 1g2 d. 2H1 1aq2 1 2CrO4 22 1aq2 S Cr2O7 22 1aq2 1 H2O1l2

The Ostwald process for the commercial production of nitric acid involves the following three steps: 4NH3 1g2 1 5O2 1g2 h 4NO1g2 1 6H2O1g2 2NO1g2 1 O2 1g2 h 2NO2 1g2 3NO2 1g2 1 H2O1l2 h 2HNO3 1aq2 1 NO1g2 a. Which reactions in the Ostwald process are oxidation reduction reactions? b. Identify each oxidizing agent and reducing agent.

What is electrochemistry? What are redox reactions? Explain the difference between a galvanic and an electrolytic cell.

When balancing equations in Chapter 3, we did not mention that reactions must be charge balanced as well as mass balanced. What do charge balanced and mass balanced mean? How are redox equations charge balanced?

When magnesium metal is added to a beaker of HCl(aq), a gas is produced. Knowing that magnesium is oxidized and that hydrogen is reduced, write the balanced equation for the reaction. How many electrons are transferred in the balanced equation? What quantity of useful work can be obtained when Mg is added directly to the beaker of HCl? How can you harness this reaction to do useful work?

How can one construct a galvanic cell from two substances, each having a negative standard reduction potential?

The free energy change for a reaction, DG, is an extensive property. What is an extensive property? Surprisingly, one can calculate DG from the cell potential, , for the reaction. This is surprising because is an intensive property. How can the extensive property DG be calculated from the intensive property ?

What is wrong with the following statement: The best concentration cell will consist of the substance having the most positive standard reduction potential. What drives a concentration cell to produce a large voltage?

When jump-starting a car with a dead battery, the ground jumper should be attached to a remote part of the engine block. Why?

In theory, most metals should easily corrode in air. Why? A group of metals called the noble metals are relatively difficult to corrode in air. Some noble metals include gold, platinum, and silver. Reference Table 18.1 to come up with a possible reason why the noble metals are relatively difficult to corrode.

Consider the electrolysis of a molten salt of some metal. What information must you know to calculate the mass of metal plated out in the electrolytic cell?

Consider the following electrochemical cell: Voltmeter or Power source Cu 1.0 M Cu2+ 1.0 M Ag+ Ag a. If silver metal is a product of the reaction, is the cell a galvanic cell or electrolytic cell? Label the cathode and anode, and describe the direction of the electron flow.b. If copper metal is a product of the reaction, is the cell a galvanic cell or electrolytic cell? Label the cathode and anode, and describe the direction of the electron flow. c. If the above cell is a galvanic cell, determine the standard cell potential. d. If the above cell is an electrolytic cell, determine the minimum external potential that must be applied to cause the reaction to occur.

Balance the following oxidationreduction reactions that occur in acidic solution using the half-reaction method. a. I 2 1aq2 1 ClO2 1aq2 S I3 2 1aq2 1 Cl2 1aq2 b. As2O3 1s2 1 NO3 2 1aq2 S H3AsO4 1aq2 1 NO1g2 c. Br2 1aq2 1 MnO4 2 1aq2 S Br2 1l2 1 Mn21 1aq2 d. CH3OH1aq2 1 Cr2O7 22 1aq2 S CH2O1aq2 1 Cr31 1aq2

Balance the following oxidationreduction reactions that occur in acidic solution using the half-reaction method. a. Cu1s2 1 NO3 2 1aq2 S Cu21 1aq2 1 NO1g2 b. Cr2O7 22 1aq2 1 Cl2 1aq2 S Cr31 1aq2 1 Cl2 1g2 c. Pb1s2 1 PbO2 1s2 1 H2SO4 1aq2 S PbSO4 1s2 d. Mn21 1aq2 1 NaBiO3 1s2 S Bi31 1aq2 1 MnO4 2 1aq2 e. H3AsO4 1aq2 1 Zn1s2 S AsH3 1g2 1 Zn21 1aq2

Balance the following oxidationreduction reactions that occur in basic solution. a. Al1s2 1 MnO4 2 1aq2 S MnO2 1s2 1 Al1OH2 4 2 1aq2 b. Cl2 1g2 S Cl2 1aq2 1 OCl2 1aq2 c. NO2 2 1aq2 1 Al1s2 S NH3 1g2 1 AlO2 2 1aq2

Balance the following oxidationreduction reactions that occur in basic solution. a. Cr1s2 1 CrO4 22 1aq2 S Cr1OH2 3 1s2 b. MnO4 2 1aq2 1 S22 1aq2 S MnS1s2 1 S1s2 c. CN2 1aq2 1 MnO4 2 1aq2 S CNO2 1aq2 1 MnO2 1s2

Chlorine gas was first prepared in 1774 by C. W. Scheele by oxidizing sodium chloride with manganese(IV) oxide. The reaction is NaCl1aq2 1 H2SO4 1aq2 1 MnO2 1s2 h Na2SO4 1aq2 1 MnCl2 1aq2 1 H2O1l2 1 Cl2 1g2 Balance this equation

Gold metal will not dissolve in either concentrated nitric acid or concentrated hydrochloric acid. It will dissolve, however, in aqua regia, a mixture of the two concentrated acids. The products of the reaction are the AuCl4 2 ion and gaseous NO. Write a balanced equation for the dissolution of gold in aqua regia.

Consider the following galvanic cell: Porous disk Anode Cathode Label the reducing agent and the oxidizing agent, and describe the direction of the electron flow.

Consider the following galvanic cell: Digital ?.?? voltmeter Zn 1.0 M Zn2+ 1.0 M Cu2+ Cu a. Label the reducing agent and the oxidizing agent, and describe the direction of the electron flow. b. Determine the standard cell potential. c. Which electrode increases in mass as the reaction proceeds, and which electrode decreases in mass?

Sketch the galvanic cells based on the following overall reactions. Show the direction of electron flow, and identify the cathode and anode. Give the overall balanced equation. Assume that all concentrations are 1.0 M and that all partial pressures are 1.0 atm. a. Cr31 1aq2 1 Cl2 1g2mCr2O7 22 1aq2 1 Cl2 1aq2 b. Cu21 1aq2 1 Mg1s2mMg21 1aq2 1 Cu1s2

Sketch the galvanic cells based on the following overall reactions. Show the direction of electron flow, the direction of ion migration through the salt bridge, and identify the cathode and anode. Give the overall balanced equation. Assume that all concentrations are 1.0 M and that all partial pressures are 1.0 atm.a. IO3 2 1aq2 1 Fe21 1aq2mFe31 1aq2 1 I2 1aq2 b. Zn1s2 1 Ag1 1aq2mZn21 1aq2 1 Ag1s

Calculate 8 values for the galvanic cells in Exercise 37

Calculate 8 values for the galvanic cells in Exercise 38.

Sketch the galvanic cells based on the following half-reactions. Show the direction of electron flow, show the direction of ion migration through the salt bridge, and identify the cathode and anode. Give the overall balanced equation, and determine 8 for the galvanic cells. Assume that all concentrations are 1.0 M and that all partial pressures are 1.0 atm. a. Cl2 1 2e2 S 2Cl2 % 5 1.36 V Br2 1 2e2 S 2Br2 % 5 1.09 V b. MnO4 2 1 8H1 1 5e2 S Mn21 1 4H2O % 5 1.51 V IO4 2 1 2H1 1 2e2 S IO3 2 1 H2O % 5 1.60 V

Sketch the galvanic cells based on the following half-reactions. Show the direction of electron flow, show the direction of ion migration through the salt bridge, and identify the cathode and anode. Give the overall balanced equation, and determine 8 for the galvanic cells. Assume that all concentrations are 1.0 M and that all partial pressures are 1.0 atm. a. H2O2 1 2H1 1 2e2 S 2H2O % 5 1.78 V O2 1 2H1 1 2e2 S H2O2 % 5 0.68 V b. Mn21 1 2e2 S Mn % 5 21.18 V Fe31 1 3e2 S Fe % 5 20.036 V

Give the standard line notation for each cell in Exercises 37 and 41.

Give the standard line notation for each cell in Exercises 38 and 42.

Consider the following galvanic cells: Au Pt 1.0 M Au3+ 1.0 M Cu+ 1.0 M Cu2+ a. Cd Pt 1.0 M Cd2+ 1.0 M VO2 + 1.0 M H+ 1.0 M VO2+ For each galvanic cell, give the balanced cell equation and determine 8. Standard reduction potentials are found in Table 18.1

Give the balanced cell equation and determine 8 for the galvanic cells based on the following half-reactions. Standard reduction potentials are found in Table 18.1. a. Cr2O7 22 1 14H1 1 6e2 S 2Cr31 1 7H2O H2O2 1 2H1 1 2e2 S 2H2O b. 2H1 1 2e2 S H2 Al31 1 3e2 S Al

Calculate 8 values for the following cells. Which reactions are spontaneous as written (under standard conditions)? Balance the equations. Standard reduction potentials are found in Table 18.1. a. MnO4 2 1aq2 1 I 2 1aq2 h I2 1aq2 1 Mn21 1aq2 b. MnO4 2 1aq2 1 F2 1aq2 h F2 1g2 1 Mn21 1aq

Calculate 8 values for the following cells. Which reactions are spontaneous as written (under standard conditions)? Balance the equations that are not already balanced. Standard reduction potentials are found in Table 18.1. a. H2 1g2 h H1 1aq2 1 H2 1aq2 b. Au31 1aq2 1 Ag1s2 h Ag1 1aq2 1 Au1s

Chlorine dioxide (ClO2), which is produced by the reaction 2NaClO2 1aq2 1 Cl2 1g2 h 2ClO2 1g2 1 2NaCl1aq2 has been tested as a disinfectant for municipal water treatment. Using data from Table 18.1, calculate 8 and DG8 at 258C for the production of ClO2.

The amount of manganese in steel is determined by changing it to permanganate ion. The steel is first dissolved in nitric acid, producing Mn21 ions. These ions are then oxidized to the deeply colored MnO4 2 ions by periodate ion (IO4 2) in acid solution. a. Complete and balance an equation describing each of the above reactions. b. Calculate 8 and DG8 at 258C for each reaction.

Calculate the maximum amount of work that can be obtained from the galvanic cells at standard conditions in Exercise 45.

Calculate the maximum amount of work that can be obtained from the galvanic cells at standard conditions in Exercise 46.

Estimate 8 for the half-reaction 2H2O 1 2e2 h H2 1 2OH2 given the following values of DG8f: H2O1l2 5 2237 kJ/mol H2 1g2 5 0.0 OH2 1aq2 5 2157 kJ/mol e2 5 0.0 Compare this value of 8 with the value of 8 given in Table 18.1

The equation DG 5 2nF % also can be applied to halfreactions. Use standard reduction potentials to estimate DG8f for Fe21(aq) and Fe31(aq). (DG8f for e2 5 0.)

Glucose is the major fuel for most living cells. The oxidative breakdown of glucose by our body to produce energy is called respiration. The reaction for the complete combustion of glucose is C6H12O6 1s2 1 6O2 1g2 h 6CO2 1g2 1 6H2O1l2 If this combustion reaction could be harnessed as a fuel cell, calculate the theoretical voltage that could be produced at standard conditions. (Hint: Use DG8f values from Appendix 4.)

Direct methanol fuel cells (DMFCs) have shown some promise as a viable option for providing green energy to small electrical devices. Calculate 8 for the reaction that takes place in DMFCs: CH3OH1l2 1 3/2O2 1g2 h CO2 1g2 1 2H2O1l2 Use values of DG8f from Appendix 4

Using data from Table 18.1, place the following in order of increasing strength as oxidizing agents (all under standard conditions). Cd21, IO3 2, K1, H2O, AuCl4 2, I2

Using data from Table 18.1, place the following in order of increasing strength as reducing agents (all under standard conditions). Cu1, F2, H2, H2O, I2, K

Answer the following questions using data from Table 18.1 (all under standard conditions). a. Is H1(aq) capable of oxidizing Cu(s) to Cu21(aq)? b. Is Fe31(aq) capable of oxidizing I2(aq)? c. Is H2(g) capable of reducing Ag1(aq)?

Answer the following questions using data from Table 18.1 (all under standard conditions). a. Is H2(g) capable of reducing Ni21(aq)? b. Is Fe21(aq) capable of reducing VO2 1(aq)? c. Is Fe21(aq) capable of reducing Cr31(aq) to Cr21(aq)?

Consider only the species (at standard conditions) Na1, Cl2, Ag1, Ag, Zn21, Zn, Pb in answering the following questions. Give reasons for your answers. (Use data from Table 18.1.) a. Which is the strongest oxidizing agent? b. Which is the strongest reducing agent? c. Which species can be oxidized by SO4 22(aq) in acid? d. Which species can be reduced by Al(s)?

Consider only the species (at standard conditions) Br2, Br2, H1, H2, La31, Ca, Cd in answering the following questions. Give reasons for your answers. a. Which is the strongest oxidizing agent? b. Which is the strongest reducing agent? c. Which species can be oxidized by MnO4 2 in acid? d. Which species can be reduced by Zn(s)?

Use the table of standard reduction potentials (Table 18.1) to pick a reagent that is capable of each of the following oxidations (under standard conditions in acidic solution). a. oxidize Br2 to Br2 but not oxidize Cl2 to Cl2 b. oxidize Mn to Mn21 but not oxidize Ni to Ni21

Use the table of standard reduction potentials (Table 18.1) to pick a reagent that is capable of each of the following reductions (under standard conditions in acidic solution). a. reduce Cu21 to Cu but not reduce Cu21 to Cu1 b. reduce Br2 to Br2 but not reduce I2 to I2

Hydrazine is somewhat toxic. Use the half-reactions shown below to explain why household bleach (a highly alkaline solution of sodium hypochlorite) should not be mixed with household ammonia or glass cleansers that contain ammonia. ClO2 1 H2O 1 2e2 h 2OH2 1 Cl2 % 5 0.90 V N2H4 1 2H2O 1 2e2 h 2NH3 1 2OH2 % 5 20.10 V

The compound with the formula TlI3 is a black solid. Given the following standard reduction potentials, Tl31 1 2e2 h Tl1 % 5 1.25 V I3 2 1 2e2 h 3I2 % 5 0.55 V would you formulate this compound as thallium(III) iodide or thallium(I) triiodide?

A galvanic cell is based on the following half-reactions at 258C: Ag1 1 e2 h Ag H2O2 1 2H1 1 2e2 h 2H2O Predict whether cell is larger or smaller than % cell for the following cases. a. [Ag1] 5 1.0 M, [H2O2] 5 2.0 M, [H1] 5 2.0 M b. [Ag1] 5 2.0 M, [H2O2] 5 1.0 M, [H1] 5 1.0 3 1027 M

Consider the concentration cell in Fig. 18.10. If the Fe21 concentration in the right compartment is changed from 0.1 M to 1 3 1027 M Fe21, predict the direction of electron flow, and designate the anode and cathode compartments

Consider the concentration cell shown below. Calculate the cell potential at 258C when the concentration of Ag1 in the compartment on the right is the following. a. 1.0 M b. 2.0 M c. 0.10 M d. 4.0 3 1025 M e. Calculate the potential when both solutions are 0.10 M in Ag1. For each case, also identify the cathode, the anode, and the direction in which electrons flow. Ag Ag [Ag+] = 1.0 M

Consider a concentration cell similar to the one shown in Exercise 69, except that both electrodes are made of Ni and in the left-hand compartment [Ni21] 5 1.0 M. Calculate the cell potential at 258C when the concentration of Ni21 in the compartment on the right has each of the following values. a. 1.0 M b. 2.0 M c. 0.10 M d. 4.0 3 1025 M e. Calculate the potential when both solutions are 2.5 M in Ni21. For each case, also identify the cathode, anode, and the direction in which electrons flow.

The overall reaction in the lead storage battery is Pb1s2 1 PbO2 1s2 1 2H1 1aq2 1 2HSO4 2 1aq2 h 2PbSO4 1s2 1 2H2O1l2 Calculate at 258C for this battery when [H2SO4] 5 4.5 M, that is, [H1] 5 [HSO4 2] 5 4.5 M. At 258C, % 5 2.04 V for the lead storage battery.

Calculate the pH of the cathode compartment for the following reaction given cell 5 3.01 V when [Cr31] 5 0.15 M, [Al31] 5 0.30 M, and [Cr2O7 22] 5 0.55 M. 2Al1s2 1 Cr2O7 22 1aq2 1 14H1 1aq2 h 2Al31 1aq2 1 2Cr31 1aq2 1 7H2O1l2

Consider the cell described below: Zn 0 Zn21 11.00 M2 0 0 Cu21 11.00 M2 0 Cu Calculate the cell potential after the reaction has operated long enough for the [Zn21] to have changed by 0.20 mol/L. (Assume T 5 258C.)

Consider the cell described below: Al 0 Al31 11.00 M2 0 0 Pb21 11.00 M2 0 Pb Calculate the cell potential after the reaction has operated long enough for the [Al31] to have changed by 0.60 mol/L. (Assume T 5 258C.)

Calculate DG8 and K at 258C for the reactions in Exercises 37 and 41.

Calculate DG8 and K at 258C for the reactions in Exercises 38 and 42.

Consider the galvanic cell based on the following halfreactions: Zn21 1 2e2 h Zn % 5 20.76 V Fe21 1 2e2 h Fe % 5 20.44 V a. Determine the overall cell reaction and calculate 8 cell. b. Calculate DG8 and K for the cell reaction at 258C. c. Calculate cell at 258C when [Zn21] 5 0.10 M and [Fe21] 5 1.0 3 1025 M.

Consider the galvanic cell based on the following halfreactions: Au31 1 3e2 h Au % 5 1.50 V Tl1 1 e2 h Tl % 5 20.34 V a. Determine the overall cell reaction and calculate 8 cell. b. Calculate DG8 and K for the cell reaction at 258C. c. Calculate cell at 258C when [Au31] 5 1.0 3 1022 M and [Tl1] 5 1.0 3 1024 M.

An electrochemical cell consists of a standard hydrogen electrode and a copper metal electrode. a. What is the potential of the cell at 258C if the copper electrode is placed in a solution in which [Cu21] 5 2.5 3 1024 M? b. The copper electrode is placed in a solution of unknown [Cu21]. The measured potential at 258C is 0.195 V. What is [Cu21]? (Assume Cu21 is reduced.)

An electrochemical cell consists of a nickel metal electrode immersed in a solution with [Ni21] 5 1.0 M separated by a porous disk from an aluminum metal electrode. a. What is the potential of this cell at 258C if the aluminum electrode is placed in a solution in which [Al31] 5 7.2 3 1023 M? b. When the aluminum electrode is placed in a certain solution in which [Al31] is unknown, the measured cell potential at 258C is 1.62 V. Calculate [Al31] in the unknown solution. (Assume Al is oxidized.)

An electrochemical cell consists of a standard hydrogen electrode and a copper metal electrode. If the copper electrode is placed in a solution of 0.10 M NaOH that is saturated with Cu(OH)2, what is the cell potential at 258C? [For Cu(OH)2, Ksp 5 1.6 3 10219.]

An electrochemical cell consists of a nickel metal electrode immersed in a solution with [Ni21] 5 1.0 M separated by a porous disk from an aluminum metal electrode immersed in a solution with [Al31] 5 1.0 M. Sodium hydroxide is added to the aluminum compartment, causing Al(OH)3(s) to precipitate. After precipitation of Al(OH)3 has ceased, the concentration of OH2 is 1.0 3 1024 M and the measured cell potential is 1.82 V. Calculate the Ksp value for Al(OH)3. Al1OH2 3 1s2mAl31 1aq2 1 3OH2 1aq2 Ksp 5 ?

Consider a concentration cell that has both electrodes made of some metal M. Solution A in one compartment of the cell contains 1.0 M M21. Solution B in the other cell compartment has a volume of 1.00 L. At the beginning of the experiment 0.0100 mole of M(NO3)2 and 0.0100 mole of Na2SO4 are dissolved in solution B (ignore volume changes), where the reaction M21 1aq2 1 SO4 22 1aq2mMSO4 1s2 occurs. For this reaction equilibrium is rapidly established, whereupon the cell potential is found to be 0.44 V at 258C. Assume that the process M21 1 2e2 h M has a standard reduction potential of 20.31 V and that no other redox process occurs in the cell. Calculate the value of Ksp for MSO4(s) at 258C.

You have a concentration cell in which the cathode has a silver electrode with 0.10 M Ag1. The anode also has a silver electrode with Ag1(aq), 0.050 M S2O3 22, and 1.0 3 1023 M Ag(S2O3)2 32. You read the voltage to be 0.76 V.a. Calculate the concentration of Ag1 at the anode. b. Determine the value of the equilibrium constant for the formation of Ag(S2O3)2 32. Ag1 1aq2 1 2S2O3 22 1aq2mAg1S2O32 2 32 1aq2 K 5 ?

Under standard conditions, what reaction occurs, if any, when each of the following operations is performed? a. Crystals of I2 are added to a solution of NaCl. b. Cl2 gas is bubbled into a solution of NaI. c. A silver wire is placed in a solution of CuCl2. d. An acidic solution of FeSO4 is exposed to air. For the reactions that occur, write a balanced equation and calculate 8, DG8, and K at 258C

A disproportionation reaction involves a substance that acts as both an oxidizing and a reducing agent, producing higher and lower oxidation states of the same element in the products. Which of the following disproportionation reactions are spontaneous under standard conditions? Calculate DG8 and K at 258C for those reactions that are spontaneous under standard conditions. a. 2Cu1 1aq2 S Cu21 1aq2 1 Cu1s2 b. 3Fe21 1aq2 S 2Fe31 1aq2 1 Fe1s2 c. HClO2 1aq2 S ClO3 2 1aq2 1 HClO1aq2 1unbalanced2 Use the half-reactions: ClO3 2 1 3H1 1 2e2 h HClO2 1 H2O % 5 1.21 V HClO2 1 2H1 1 2e2 h HClO 1 H2O % 5 1.65 V

Consider the following galvanic cell at 258C: Pt 0 Cr21 10.30 M2, Cr31 12.0 M2 0 0 Co21 10.20 M2 0 Co The overall reaction and equilibrium constant value are 2Cr21 1aq2 1 Co21 1aq2 h 2Cr31 1aq2 1 Co1s2 K 5 2.79 3 107 Calculate the cell potential, , for this galvanic cell and DG for the cell reaction at these conditions

An electrochemical cell consists of a silver metal electrode immersed in a solution with [Ag1] 5 1.0 M separated by a porous disk from a copper metal electrode. If the copper electrode is placed in a solution of 5.0 M NH3 that is also 0.010 M in Cu(NH3)4 21, what is the cell potential at 258C? Cu21 1aq2 1 4NH3 1aq2mCu1NH32 4 21 1aq2 K 5 1.0 3 1013

Calculate Ksp for iron(II) sulfide given the following data: FeS1s2 1 2e2 h Fe1s2 1 S22 1aq2 % 5 21.01 V Fe21 1aq2 1 2e2 h Fe1s2 % 5 20.44 V

For the following half-reaction, % 5 22.07 V: AlF6 32 1aq2 1 3e2 h Al1s2 1 6F2 1aq2 Using data from Table 18.1, calculate the equilibrium constant at 258C for the reaction Al31 1aq2 1 6F2 1aq2mAlF6 32 1aq2 K 5 ?

Calculate 8 for the following half-reaction: AgI1s2 1 e2 h Ag1s2 1 I 2 1aq2 (Hint: Reference the Ksp value for AgI and the standard reduction potential for Ag1.)

The solubility product for CuI(s) is 1.1 3 10212. Calculate the value of 8 for the half-reaction CuI1s2 1 e2 h Cu1s2 1 I 2 1aq2

How long will it take to plate out each of the following with a current of 100.0 A? a. 1.0 kg Al from aqueous Al31 b. 1.0 g Ni from aqueous Ni21 c. 5.0 moles of Ag from aqueous Ag1

The electrolysis of BiO1 produces pure bismuth. How long would it take to produce 10.0 g Bi by the electrolysis of a BiO1 solution using a current of 25.0 A?

What mass of each of the following substances can be produced in 1.0 h with a current of 15 A? a. Co from aqueous Co21 b. Hf from aqueous Hf 41 c. I2 from aqueous KI d. Cr from molten CrO

Aluminum is produced commercially by the electrolysis of Al2O3 in the presence of a molten salt. If a plant has a continuous capacity of 1.00 million A, what mass of aluminum can be produced in 2.00 h?

An unknown metal M is electrolyzed. It took 74.1 s for a current of 2.00 A to plate out 0.107 g of the metal from a solution containing M(NO3)3. Identify the metal.

Electrolysis of an alkaline earth metal chloride using a current of 5.00 A for 748 s deposits 0.471 g of metal at the cathode. What is the identity of the alkaline earth metal chloride?

What volume of F2 gas, at 258C and 1.00 atm, is produced when molten KF is electrolyzed by a current of 10.0 A for 2.00 h? What mass of potassium metal is produced? At which electrode does each reaction occur?

What volumes of H2(g) and O2(g) at STP are produced from the electrolysis of water by a current of 2.50 A in 15.0 min?

A single HallHeroult cell (as shown in Fig. 18.22) produces about 1 ton of aluminum in 24 h. What current must be used to accomplish this?

A factory wants to produce 1.00 3 103 kg barium from the electrolysis of molten barium chloride. What current must be applied for 4.00 h to accomplish this?

It took 2.30 min using a current of 2.00 A to plate out all the silver from 0.250 L of a solution containing Ag1. What was the original concentration of Ag1 in the solution?

A solution containing Pt41 is electrolyzed with a current of 4.00 A. How long will it take to plate out 99% of the platinum in 0.50 L of a 0.010-M solution of Pt41?

A solution at 258C contains 1.0 M Cd21, 1.0 M Ag1, 1.0 M Au31, and 1.0 M Ni21 in the cathode compartment of an electrolytic cell. Predict the order in which the metals will plate out as the voltage is gradually increased.

Consider the following half-reactions: IrCl6 32 1 3e2 h Ir 1 6Cl2 % 5 0.77 V PtCl4 22 1 2e2 h Pt 1 4Cl2 % 5 0.73 V PdCl4 22 1 2e2 h Pd 1 4Cl2 % 5 0.62 V A hydrochloric acid solution contains platinum, palladium, and iridium as chloro-complex ions. The solution is a constant 1.0 M in chloride ion and 0.020 M in each complex ion. Is it feasible to separate the three metals from this solution by electrolysis? (Assume that 99% of a metal must be plated out before another metal begins to plate out.)

In the electrolysis of an aqueous solution of Na2SO4, what reactions occur at the anode and the cathode (assuming standard conditions)? % S2O8 22 1 2e2 h 2SO4 22 O2 1 4H1 1 4e2 h 2H2O 2H2O 1 2e2 h H2 1 2OH2 Na1 1 e2 h Na 2.01 V 1.23 V 20.83 V 22.71 V

Copper can be plated onto a spoon by placing the spoon in an acidic solution of CuSO4(aq) and connecting it to a copper strip via a power source as illustrated below: Power source Cu2+ a. Label the anode and cathode, and describe the direction of the electron flow. b. Write out the chemical equations for the reactions that occur at each electrode.

What reactions take place at the cathode and the anode when each of the following is electrolyzed? a. molten NiBr2 b. molten AlF3 c. molten MnI2

What reaction will take place at the cathode and the anode when each of the following is electrolyzed? a. molten KF b. molten CuCl2 c. molten MgI2

What reactions take place at the cathode and the anode when each of the following is electrolyzed? (Assume standard conditions.) a. 1.0 M NiBr2 solution b. 1.0 M AlF3 solution c. 1.0 M MnI2 solution

What reaction will take place at the cathode and the anode when each of the following is electrolyzed? (Assume standard conditions.) a. 1.0 M KF solution b. 1.0 M CuCl2 solution c. 1.0 M MgI2 solution

Gold is produced electrochemically from an aqueous solution of Au(CN)2 2 containing an excess of CN2. Gold metal and oxygen gas are produced at the electrodes. What amount (moles) of O2 will be produced during the production of 1.00 mole of gold?

The blood alcohol (C2H5OH) level can be determined by titrating a sample of blood plasma with an acidic potassium dichromate solution, resulting in the production of Cr31(aq) and carbon dioxide. The reaction can be monitored because the dichromate ion (Cr2O7 22) is orange in solution, and the Cr31 ion is green. The unbalanced redox equation is Cr2O7 22 1aq2 1 C2H5OH1aq2 h Cr31 1aq2 1 CO2 1g2 If 31.05 mL of 0.0600 M potassium dichromate solution is required to titrate 30.0 g blood plasma, determine the mass percent of alcohol in the blood.

The saturated calomel electrode, abbreviated SCE, is often used as a reference electrode in making electrochemical measurements. The SCE is composed of mercury in contact with a saturated solution of calomel (Hg2Cl2). The electrolyte solution is saturated KCl. SCE is 10.242 V relative to the standard hydrogen electrode. Calculate the potential for each of the following galvanic cells containing a saturated calomel electrode and the given half-cell components at standard conditions. In each case, indicate whether the SCE is the cathode or the anode. Standard reduction potentials are found in Table 18.1. a. Cu21 1 2e2 h Cu d. Al31 1 3e2 h Al b. Fe31 1 e2 h Fe21 e. Ni21 1 2e2 h Ni c. AgCl 1 e2 h Ag 1 Cl2

Consider the following half-reactions: Pt21 1 2e2 h Pt % 5 1.188 V PtCl4 22 1 2e2 h Pt 1 4Cl2 % 5 0.755 V NO3 2 1 4H1 1 3e2 h NO 1 2H2O % 5 0.96 V Explain why platinum metal will dissolve in aqua regia (a mixture of hydrochloric and nitric acids) but not in either concentrated nitric or concentrated hydrochloric acid individually

Consider the standard galvanic cell based on the following half-reactions: Cu21 1 2e2 h Cu Ag1 1 e2 h Ag The electrodes in this cell are Ag(s) and Cu(s). Does the cell potential increase, decrease, or remain the same when the following changes occur to the standard cell? a. CuSO4(s) is added to the copper half-cell compartment (assume no volume change). b. NH3(aq) is added to the copper half-cell compartment. [Hint: Cu21 reacts with NH3 to form Cu(NH3)4 21(aq).] c. NaCl(s) is added to the silver half-cell compartment. [Hint: Ag1 reacts with Cl2 to form AgCl(s).] d. Water is added to both half-cell compartments until the volume of solution is doubled. e. The silver electrode is replaced with a platinum electrode. Pt21 1 2e2 h Pt % 5 1.19 V

A standard galvanic cell is constructed so that the overall cell reaction is 2Al31 1aq2 1 3M1s2 h 3M21 1aq2 1 2Al1s2 where M is an unknown metal. If DG8 5 2411 kJ for the overall cell reaction, identify the metal used to construct the standard cell

The black silver sulfide discoloration of silverware can be removed by heating the silver article in a sodium carbonate solution in an aluminum pan. The reaction is 3Ag2S1s2 1 2Al1s2m6Ag1s2 1 3S22 1aq2 1 2Al31 1aq2 a. Using data in Appendix 4, calculate DG8, K, and 8 for the above reaction at 258C. [For Al31(aq), DG8f 5 2480. kJ/mol.] b. Calculate the value of the standard reduction potential for the following half-reaction: 2e2 1 Ag2S1s2 h 2Ag1s2 1 S22 1aq

In 1973 the wreckage of the Civil War ironclad USS Monitor was discovered near Cape Hatteras, North Carolina. [The Monitor and the CSS Virginia (formerly the USS Merrimack) fought the first battle between iron-armored ships.] In 1987 investigations were begun to see if the ship could be salvaged. It was reported in Time (June 22, 1987) that scientists were considering adding sacrificial anodes of zinc to the rapidly corroding metal hull of the Monitor. Describe how attaching zinc to the hull would protect the Monitor from further corrosion

When aluminum foil is placed in hydrochloric acid, nothing happens for the first 30 seconds or so. This is followed by vigorous bubbling and the eventual disappearance of the foil. Explain these observations.

Which of the following statements concerning corrosion is(are) true? For the false statements, correct them. a. Corrosion is an example of an electrolytic process. b. Corrosion of steel involves the reduction of iron coupled with the oxidation of oxygen. c. Steel rusts more easily in the dry (arid) Southwest states than in the humid Midwest states. d. Salting roads in the winter has the added benefit of hindering the corrosion of steel. e. The key to cathodic protection is to connect via a wire a metal more easily oxidized than iron to the steel surface to be protected.

A fuel cell designed to react grain alcohol with oxygen has the following net reaction: C2H5OH1l2 1 3O2 1g2 h 2CO2 1g2 1 3H2O1l2 The maximum work that 1 mole of alcohol can do is 1.32 3 103 kJ. What is the theoretical maximum voltage this cell can achieve at 258C?

The overall reaction and equilibrium constant value for a hydrogenoxygen fuel cell at 298 K is 2H2 1g2 1 O2 1g2 h 2H2O1l2 K 5 1.28 3 1083 a. Calculate 8 and DG8 at 298 K for the fuel cell reaction. b. Predict the signs of DH8 and DS8 for the fuel cell reaction. c. As temperature increases, does the maximum amount of work obtained from the fuel cell reaction increase, decrease, or remain the same? Explain

What is the maximum work that can be obtained from a hydrogenoxygen fuel cell at standard conditions that produces 1.00 kg water at 258C? Why do we say that this is the maximum work that can be obtained? What are the advantages and disadvantages in using fuel cells rather than the corresponding combustion reactions to produce electricity?

The overall reaction and standard cell potential at 258C for the rechargeable nickelcadmium alkaline battery is Cd1s2 1 NiO2 1s2 1 2H2O1l2 h Ni1OH2 2 1s2 1 Cd1OH2 2 1s2 % 5 1.10 V For every mole of Cd consumed in the cell, what is the maximum useful work that can be obtained at standard conditions?

An experimental fuel cell has been designed that uses carbon monoxide as fuel. The overall reaction is 2CO1g2 1 O2 1g2 h 2CO2 1g2 The two half-cell reactions are CO 1 O22 h CO2 1 2e2 O2 1 4e2 h 2O22 The two half-reactions are carried out in separate compartments connected with a solid mixture of CeO2 and Gd2O3. Oxide ions can move through this solid at high temperatures (about 8008C). DG for the overall reaction at 8008C under certain concentration conditions is 2380 kJ. Calculate the cell potential for this fuel cell at the same temperature and concentration conditions

The ultimate electron acceptor in the respiration process is molecular oxygen. Electron transfer through the respiratory chain takes place through a complex series of oxidation reduction reactions. Some of the electron transport steps use iron-containing proteins called cytochromes. All cytochromes transport electrons by converting the iron in the cytochromes from the 13 to the 12 oxidation state. Consider the following reduction potentials for three different cytochromes used in the transfer process of electrons to oxygen (the potentials have been corrected for pH and for temperature): cytochrome a1Fe312 1 e2 h cytochrome a1Fe212 % 5 0.385 V cytochrome b1Fe312 1 e2 h cytochrome b1Fe212 % 5 0.030 V cytochrome c1Fe312 1 e2 h cytochrome c1Fe212 % 5 0.254 V In the electron transfer series, electrons are transferred from one cytochrome to another. Using this information, determine the cytochrome order necessary for spontaneous transport of electrons from one cytochrome to another, which eventually will lead to electron transfer to O2.

One of the few industrial-scale processes that produce organic compounds electrochemically is used by the Monsanto Company to produce 1,4-dicyanobutane. The reduction reaction is 2CH2wCHCN 1 2H1 1 2e2 h NCi 1CH22 4iCN The NCO(CH2)4OCN is then chemically reduced using hydrogen gas to H2NO(CH2)6ONH2, which is used in the production of nylon. What current must be used to produce 150. kg NCO(CH2)4OCN per hour?

It took 150. s for a current of 1.25 A to plate out 0.109 g of a metal from a solution containing its cations. Show that it is not possible for the cations to have a charge of 11

It takes 15 kWh (kilowatt-hours) of electrical energy to produce 1.0 kg aluminum metal from aluminum oxide by the HallHeroult process. Compare this to the amount of energy necessary to melt 1.0 kg aluminum metal. Why is it economically feasible to recycle aluminum cans? [The enthalpy of fusion for aluminum metal is 10.7 kJ/mol (1 watt 5 1 J/s).]

In the electrolysis of a sodium chloride solution, what volume of H2(g) is produced in the same time it takes to produce 257 L Cl2(g), with both volumes measured at 50.8C and 2.50 atm?

Which of the following statement(s) is/are true? a. Copper metal can be oxidized by Ag1 (at standard conditions). b. In a galvanic cell the oxidizing agent in the cell reaction is present at the anode. c. In a cell using the half reactions Al31 1 3e2 8n Al and Mg21 1 2e2 8n Mg, aluminum functions as the anode. d. In a concentration cell electrons always flow from the compartment with the lower ion concentration to the compartment with the higher ion concentration. e. In a galvanic cell the negative ions in the salt bridge flow in the same direction as the electrons.

Consider a galvanic cell based on the following half-reactions: 8 (V) La31 1 3e2 8n La 22.37 Fe21 1 2e2 8n Fe 20.44 a. What is the expected cell potential with all components in their standard states?b. What is the oxidizing agent in the overall cell reaction? c. What substances make up the anode compartment? d. In the standard cell, in which direction do the electrons flow? e. How many electrons are transferred per unit of cell reaction? f. If this cell is set up at 258C with [Fe21] 5 2.00 3 1024 M and [La31] 5 3.00 3 1023 M, what is the expected cell potential?

Consider a galvanic cell based on the following theoretical half-reactions: 8 (V) M41 1 4e2 8n M 0.66 N31 1 3e2 8n N 0.39 What is the value of DG8 and K for this cell?

Consider a galvanic cell based on the following half-reactions: 8 (V) Au31 1 3e2 8n Au 1.50 Mg21 1 2e2 8n Mg 22.37 a. What is the standard potential for this cell? b. A nonstandard cell is set up at 258C with [Mg21] 5 1.00 3 1025 M. The cell potential is observed to be 4.01 V. Calculate [Au31] in this cell

An electrochemical cell consists of a silver metal electrode immersed in a solution with [Ag1] 5 1.00 M separated by a porous disk from a compartment with a copper metal electrode immersed in a solution of 10.00 M NH3 that also contains 2.4 3 1023 M Cu(NH3)4 21. The equilibrium between Cu21 and NH3 is: Cu21 1aq2 1 4NH3 1aq2mCu1NH32 4 21 1aq2 K 5 1.0 3 1013 and the two cell half-reactions are: Ag1 1 e2 h Ag % 5 0.80 V Cu21 1 2e2 h Cu % 5 0.34 V Assuming Ag1 is reduced, what is the cell potential at 25C?

An aqueous solution of PdCl2 is electrolyzed for 48.6 seconds, and during this time 0.1064 g of Pd is deposited on the cathode. What is the average current used in the electrolysis?

Balance the following equations by the half-reaction method. a. Fe1s2 1 HCl1aq2 h HFeCl4 1aq2 1 H2 1g2 b. IO3 2 1aq2 1 I 2 1aq2 hAcid I3 2 1aq2 c. Cr1NCS2 6 42 1aq2 1 Ce41 1aq2 hAcid Cr31 1aq2 1 Ce31 1aq2 1 NO3 2 1aq2 1 CO2 1g2 1 SO4 22 1aq2 d. CrI3 1s2 1 Cl2 1g2 hBase CrO4 22 1aq2 1 IO4 2 1aq2 1 Cl2 1aq2 e. Fe1CN2 6 42 1aq2 1 Ce41 1aq2 hBase Ce1OH2 3 1s2 1 Fe1OH2 3 1s2 1 CO3 22 1aq2 1 NO3 2 1aq2

Combine the equations DG 5 2nF% and DG 5 DH 2 TDS to derive an expression for 8 as a function of temperature. Describe how one can graphically determine DH8 and DS8 from measurements of 8 at different temperatures, assuming that DH8 and DS8 do not depend on temperature. What property would you look for in designing a reference half-cell that would produce a potential relatively stable with respect to temperature?

The overall reaction in the lead storage battery is Pb1s2 1 PbO2 1s2 1 2H1 1aq2 1 2HSO4 2 1aq2 h 2PbSO4 1s2 1 2H2O1l2 a. For the cell reaction DH8 5 2315.9 kJ and DS8 5 263.5 J/K. Calculate 8 at 220.8C. Assume DH8 and DS8 do not depend on temperature. b. Calculate at 220.8C when [HSO4 2] 5 [H1] 5 4.5 M. c. Consider your answer to Exercise 71. Why does it seem that batteries fail more often on cold days than on warm days?

Consider the following galvanic cell: Pb Ag 1.8 M Pb2+ ? M Ag+ ? M SO4 2- 0.83 V Ag2SO4 (s) Calculate the Ksp value for Ag2SO4(s). Note that to obtain silver ions in the right compartment (the cathode compartment), excess solid Ag2SO4 was added and some of the salt dissolved.

A zinccopper battery is constructed as follows at 258C: Zn 0 Zn21 10.10 M2 0 0 Cu21 12.50 M2 0 Cu The mass of each electrode is 200. g. a. Calculate the cell potential when this battery is first connected. b. Calculate the cell potential after 10.0 A of current has flowed for 10.0 h. (Assume each half-cell contains 1.00 L of solution.) c. Calculate the mass of each electrode after 10.0 h. d. How long can this battery deliver a current of 10.0 A before it goes dead?

A galvanic cell is based on the following half-reactions: Fe21 1 2e2 h Fe1s2 % 5 20.440 V 2H1 1 2e2 h H2 1g2 % 5 0.000 V where the iron compartment contains an iron electrode and [Fe21] 5 1.00 3 1023 M and the hydrogen compartment contains a platinum electrode, PH2 5 1.00 atm, and a weak acid, HA, at an initial concentration of 1.00 M. If the observed cell potential is 0.333 V at 258C, calculate the Ka value for the weak acid HA

Consider a cell based on the following half-reactions: Au31 1 3e2 h Au % 5 1.50 V Fe31 1 e2 h Fe21 % 5 0.77 V a. Draw this cell under standard conditions, labeling the anode, the cathode, the direction of electron flow, and the concentrations, as appropriate. b. When enough NaCl(s) is added to the compartment containing gold to make the [Cl2] 5 0.10 M, the cell potential is observed to be 0.31 V. Assume that Au31 is reduced and assume that the reaction in the compartment containing gold is Au31 1aq2 1 4Cl2 1aq2mAuCl4 2 1aq2 Calculate the value of K for this reaction at 258C.

The measurement of pH using a glass electrode obeys the Nernst equation. The typical response of a pH meter at 25.008C is given by the equation %meas 5 %ref 1 0.05916 pH where ref contains the potential of the reference electrode and all other potentials that arise in the cell that are not related to the hydrogen ion concentration. Assume that ref 5 0.250 V and that meas 5 0.480 V. a. What is the uncertainty in the values of pH and [H1] if the uncertainty in the measured potential is 61 mV (60.001 V)? b. To what precision must the potential be measured for the uncertainty in pH to be 60.02 pH unit?

You have a concentration cell with Cu electrodes and [Cu21] 5 1.00 M (right side) and 1.0 3 1024 M (left side). a. Calculate the potential for this cell at 25C. b. The Cu21 ion reacts with NH3 to form Cu(NH3)4 21 by the following equation: Cu21 1aq2 1 4NH3 1aq2mCu1NH32 4 21 1aq2 K 5 1.0 3 1013 Calculate the new cell potential after enough NH3 is added to the left cell compartment such that at equilibrium [NH3] 5 2.0 M.

A galvanic cell is based on the following half-reactions: Ag1 1 e2 h Ag1s2 % 5 0.80 V Cu21 1 2e2 h Cu1s2 % 5 0.34 V In this cell, the silver compartment contains a silver electrode and excess AgCl(s) (Ksp 5 1.6 3 10210), and the copper compartment contains a copper electrode and [Cu21] 5 2.0 M. a. Calculate the potential for this cell at 258C. b. Assuming 1.0 L of 2.0 M Cu21 in the copper compartment, calculate the moles of NH3 that would have to be added to give a cell potential of 0.52 V at 258C (assume no volume change on addition of NH3). Cu21 1aq2 1 4NH3 1aq2m Cu1NH32 4 21 1aq2 K 5 1.0 3 1013

Given the following two standard reduction potentials, M31 1 3e2 h M % 5 20.10 V M21 1 2e2 h M % 5 20.50 V solve for the standard reduction potential of the half-reaction M31 1 e2 h M21 (Hint: You must use the extensive property DG8 to determine the standard reduction potential.)

Consider the following galvanic cell: Ni Ag 1.0 M Ni2+ 1.0 M Ag+ Calculate the concentrations of Ag1(aq) and Ni21(aq) once the cell is dead.

A chemist wishes to determine the concentration of CrO4 22 electrochemically. A cell is constructed consisting of a saturated calomel electrode (SCE; see Exercise 115) and a silver wire coated with Ag2CrO4. The 8 value for the following half-reaction is 0.446 V relative to the standard hydrogen electrode: Ag2CrO4 1 2e2 h 2Ag 1 CrO4 22 a. Calculate cell and DG at 258C for the cell reaction when [CrO4 22] 5 1.00 mol/L. b. Write the Nernst equation for the cell. Assume that the SCE concentrations are constant. c. If the coated silver wire is placed in a solution (at 258C) in which [CrO4 22] 5 1.00 3 1025 M, what is the expected cell potential? d. The measured cell potential at 258C is 0.504 V when the coated wire is dipped into a solution of unknown [CrO4 22]. What is [CrO4 22] for this solution? e. Using data from this problem and from Table 18.1, calculate the solubility product (Ksp) for Ag2CrO4.

Consider the following galvanic cell: Ag Cd 1.00 M Ag+ 1.00 M Cd2+ A 15.0-mole sample of NH3 is added to the Ag compartment (assume 1.00 L of total solution after the addition). The silver ion reacts with ammonia to form complex ions as shown: Ag1 1aq2 1 NH3 1aq2mAgNH3 1 1aq2 K1 5 2.1 3 103 AgNH3 1 1aq2 1 NH3 1aq2mAg1NH32 2 1 1aq2 K2 5 8.2 3 103 Calculate the cell potential after the addition of 15.0 moles of NH3.

When copper reacts with nitric acid, a mixture of NO(g) and NO2(g) is evolved. The volume ratio of the two product gases depends on the concentration of the nitric acid according to the equilibrium 2H1 1aq2 1 2NO3 2 1aq2 1 NO1g2m3NO2 1g2 1 H2O1l2 Consider the following standard reduction potentials at 258C: 3e2 1 4H1 1aq2 1 NO3 2 1aq2 h NO1g2 1 2H2O1l2 % 5 0.957 V e2 1 2H1 1aq2 1 NO3 2 1aq2 h NO2 1g2 1 2H2O1l2 % 5 0.775 V a. Calculate the equilibrium constant for the above reaction. b. What concentration of nitric acid will produce a NO and NO2 mixture with only 0.20% NO2 (by moles) at 258C and 1.00 atm? Assume that no other gases are present and that the change in acid concentration can be neglected.

The following standard reduction potentials have been determined for the aqueous chemistry of indium: In31 1aq2 1 2e2 h In1 1aq2 % 5 20.444 V In1 1aq2 1 e2 h In1s2 % 5 20.126 V a. What is the equilibrium constant for the disproportionation reaction, where a species is both oxidized and reduced, shown below? 3In1 1aq2 h 2In1s2 1 In31 1aq2 b. What is DG8f for In1(aq) if DG8f 5 297.9 kJ/mol for In31(aq)?

An electrochemical cell is set up using the following unbalanced reaction: Ma1 1aq2 1 N1s2 h N21 1aq2 1 M1s2 The standard reduction potentials are: Ma1 1 ae2 h M % 5 0.400 V N21 1 2e2 h N % 5 0.240 V The cell contains 0.10 M N21 and produces a voltage of 0.180 V. If the concentration of Ma1 is such that the value of the reaction quotient Q is 9.32 3 1023 , calculate [Ma1]. Calculate wmax for this electrochemical cell.

Three electrochemical cells were connected in series so that the same quantity of electrical current passes through all three cells. In the first cell, 1.15 g chromium metal was deposited from a chromium(III) nitrate solution. In the second cell, 3.15 g osmium was deposited from a solution made of Osn1 and nitrate ions. What is the name of the salt? In the third cell, the electrical charge passed through a solution containing X21 ions caused deposition of 2.11 g metallic X. What is the electron configuration of X?

A silver concentration cell is set up at 25C as shown below: Digital 0.58 voltmeter 1.0 M Cl AgCl ? M Ag+ 1.0 M Ag+ The AgCl(s) is in excess in the left compartment. a. Label the anode and cathode, and describe the direction of the electron flow. b. Determine the value of Ksp for AgCl at 25C.

A galvanic cell is based on the following half-reactions: Cu21 1aq2 1 2e2 h Cu1s2 % 5 0.34 V V21 1aq2 1 2e2 h V1s2 % 5 21.20 V In this cell, the copper compartment contains a copper electrode and [Cu21] 5 1.00 M, and the vanadium compartment contains a vanadium electrode and V21 at an unknown concentration. The compartment containing the vanadium (1.00 L of solution) was titrated with 0.0800 M H2EDTA22, resulting in the reaction H2EDTA22 1aq2 1 V21 1aq2 mVEDTA22 1aq2 1 2H1 1aq2 K 5 ? The potential of the cell was monitored to determine the stoichiometric point for the process, which occurred at a volume of 500.0 mL H2EDTA22 solution added. At the stoichiometric point, cell was observed to be 1.98 V. The solution was buffered at a pH of 10.00. a. Calculate cell before the titration was carried out. b. Calculate the value of the equilibrium constant, K, for the titration reaction. c. Calculate cell at the halfway point in the titration.

The table below lists the cell potentials for the 10 possible galvanic cells assembled from the metals A, B, C, D, and E, and their respective 1.00 M 21 ions in solution. Using the data in the table, establish a standard reduction potential table similar to Table 18.1 in the text. Assign a reduction potential of 0.00 V to the half-reaction that falls in the middle of the series. You should get two different tables. Explain why, and discuss what you could do to determine which table is correct.

An aqueous solution of an unknown salt of ruthenium is electrolyzed by a current of 2.50 A passing for 50.0 min. If 2.618 g Ru is produced at the cathode, what is the charge on the ruthenium ions in solution?