20. Electrochemistry

What are the products of the overall reaction in the elec-trolysis of an aqueous solution of sodium hydroxide? (Refer to Table 19.1 for standard reduction potentials.) (a) Na(s) and O2(g) (b) H2(g) and O2(g) (c) Na(s) and H2(g) (d) Na(s) and H2O2(aq)

During the discharge of an alkaline battery, 4.50 g of Zn is consumed at the anode of the battery. (b) How many coulombs of electrical charge are transferred from Zn to MnO2?

Li-ion batteries used in automobiles typically use a LiMn2O4 cathode in place of the LiCoO2 cathode found in most Li-ion batteries. (c) In a battery that uses a LiCoO2 cathode, approximately 50% of the lithium migrates from the cathode to the anode on charging. In a battery that uses a LiMn2O4 cathode, what fraction of the lithium in LiMn2O4 would need to migrate out of the cathode to deliver the same amount of lithium to the graphite anode?

Li-ion batteries used in automobiles typically use a LiMn2O4 cathode in place of the LiCoO2 cathode found in most Li-ion batteries. (b) Which material has a higher percentage of lithium? Does this help to explain why batteries made with LiMn2O4 cathodes deliver less power on discharging?

Determine the optimum mass ratio of Zn to MnO2 in an alka- line battery.

What mass of lead sulfate is formed in a lead–acid storage bat- tery when 1.00 g of Pb undergoes oxidation?

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron. c. Mn

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron. b. Sn

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron. a. Zn

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron. c. Cu

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron. b. Cr

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron. a. Mg

(d) Why is sodium metal not obtained when an aqueous solution of NaCl undergoes electrolysis?

(c) What process occurs at the anode in the electrolysis of molten NaCl?

(d) Why are active metals such as Al obtained by electrolysis using molten salts rather than aqueous solutions?

(a) A Cr3+1aq2 solution is electrolyzed, using a current of 7.60 A. What mass of Cr(s) is plated out after 2.00 days?

(a) Calculate the mass of Li formed by electrolysis of molten LiCl by a current of 7.5 * 104 A flowing for a period of 24 h. Assume the electrolytic cell is 85% efficient. (b) What is the minimum voltage required to drive the reaction?

What products are obtained in the electrolysis of a molten mix- ture of KI and KBr?

Write equations for the half-reactions that occur at the anode and cathode for the electrolysis of each aqueous solution. a. Ni(NO3)2(aq)

A mixture of copper and gold metals that is subjected to electrorefining contains tellurium as an impurity. The standard reduction potential between tellurium and its lowest common oxidation state, Te4+, is Te4+1aq2 + 4 e- ¡ Te1s2 E°red = 0.57 V Given this information, describe the probable fate of tellurium impurities during electrorefining. Do the impurities fall to the bottom of the refining bath, unchanged, as copper is oxidized, or do they go into solution as ions? If they go into solution, do they plate out on the cathode?

Silver can be electroplated at the cathode of an electrolysis cell by the half-reaction: Ag+(aq) + e- ¡ Ag(s) What mass of silver would plate onto the cathode if a current of 6.8 A flowed through the cell for 72 min?

A major source of sodium metal is the electrolysis of molten so- dium chloride. What magnitude of current produces 1.0 kg of sodium metal in 1 hour?

Calculate the number of kilowatt-hours of electricity required to produce 1.0 * 103 kg (1 metric ton) of aluminum by electrolysis of Al3+ if the applied voltage is 4.50 V and the process is 45% efficient.

A battery relies on the oxidation of magnesium and the reduction of Cu2+. The initial concentrations of Mg2+ and Cu2+ are 1.0 * 10-4 M and 1.5 M, respectively, in 1.0-liter half-cells. c. How long can the battery deliver 5.0 A before going dead?

A rechargeable battery is constructed based on a concentration cell constructed of two Ag/Ag+ half-cells. The volume of each half-cell is 2.0 L, and the concentrations of Ag+ in the half-cells are 1.25 M and 1.0 * 10-3 M. c. Upon recharging, how long would it take to redissolve 1.00 * 102 g of silver at a charging current of 10.0 amps?

A rechargeable battery is constructed based on a concentration cell constructed of two Ag/Ag+ half-cells. The volume of each half-cell is 2.0 L, and the concentrations of Ag+ in the half-cells are 1.25 M and 1.0 * 10-3 M. b. What mass of silver is plated onto the cathode by running at 3.5 A for 5.5 h?

A student designs an ammeter (a device that measures electrical current) that is based on the electrolysis of water into hydrogen and oxygen gases. When electrical current of unknown magnitude is run through the device for 2.00 min, 12.3 mL of water-saturated H21g2 is collected. The temperature of the system is 25.5 °C, and the atmospheric pressure is 768 torr. What is the magnitude of the current in amperes?

A metal forms the fluoride MF3. Electrolysis of the molten fluo- ride by a current of 3.86 A for 16.2 minutes deposits 1.25 g of the metal. Calculate the molar mass of the metal.

A sample of impure tin of mass 0.535 g is dissolved in strong acid to give a solution of Sn2+. The solution is then titrated with a 0.0448 M solution of NO3-, which is reduced to NO(g). The equivalence point is reached upon the addition of 0.0344 L of the NO3- solution. Find the percent by mass of tin in the original sample, assuming that it contains no other reducing agents.

Which of the following describes the process of galvanization that protects steel from rusting? (a) Steel is coated with a layer of paint. (b) Iron in steel is oxidized to form a protective oxide coating. (c) Steel is coated with zinc because zinc is more easily oxidized than iron. (d) A strip of magnesium is attached to steel because the magnesium is more easily oxidized than iron.

A current of 11.3 A is applied to 1.25 L of a solution of 0.552 M HBr converting some of the H+ to H2(g), which bubles out of solution. What is the pH of the solution after 73 minutes?

What is meant by cathodic protection? (a) Steel is coated with a layer of paint. (b) Iron in steel is oxidized to form a protective oxide coating. (c) Steel is coated with zinc because zinc is more easily oxidized than iron. (d) A strip of magnesium is attached to steel because the magnesium is more easily oxidized than iron.

Which of the following metals can offer cathodic protec-tion to iron? Select all the correct choices. Mn, Ni, Pb, Sn, Al

(a) Sketch a cell with inert electrodes suitable for the elec-trolysis of an aqueous solution of sulfuric acid. Label the anode and cathode, and indicate the direction of electron and ion flow. Identify the positive and negative electrodes. (b) Write balanced equations for the anode, cathode, and overall cell reactions.

What products should be formed when the following reac-tants are electrolyzed in a cell having inert electrodes? Account for any differences. (b) Aqueous KCl

Predict the anode, cathode, and overall cell reactions when an aqueous solution of each of the following salts is electrolyzed in a cell having inert electrodes. (c) LiOH

Predict the anode, cathode, and overall cell reactions when an aqueous solution of each of the following salts is electrolyzed in a cell having inert electrodes. (b) CuCl2

Predict the anode, cathode, and overall cell reactions when an aqueous solution of each of the following salts is electrolyzed in a cell having inert electrodes. (a) Ag2SO4

How many hours are required to produce 1.00 * 103 kg of sodium by the electrolysis of molten NaCl with a constant current of 3.00 * 104 A? How many liters of Cl2 at STP will be obtained as a by-product?

What constant current (in amperes) is required to produce aluminum by the Hall–Héroult process at a rate of 40.0 kg/h?

Electrolysis of a metal nitrate solution M(NO3)2(aq) for 325 min with a constant current of 20.0 A gives 111 g of the metal. Identify the metal ion M2+.

Aluminum, titanium, and several other metals can be col-ored by an electrochemical process called anodizing. Anodizing oxidizes a metal anode to yield a porous metal oxide coating that can incorporate dye molecules to give brilliant colors. In the oxidation of aluminum, for instance, the electrode reactions are The thickness of the aluminum oxide coating that forms on the anode can be controlled by varying the current flow during the electrolysis. How many minutes are required to produce a 0.0100-mm thick coating of Al2O3 (density 3.97 g/cm^3) on a square piece of aluminum metal 10.0 cm on an edge if the current passed through the piece is 0.600 A?

In order to charge a lead storage battery (Section 19.10) 500.0 g of PbSO4(s) must be converted into PbO2(s) and Pb(s). (b) How many coulombs of electrical charge are needed?

The sodium–sulfur battery has molybdenum electrodes with anode and cathode compartments separated by b-alumina, a ceramic through which sodium ions can pass. Because the battery operates at temperatures above 300 °C, all the reactants and products are present in a molten solution. The cell voltage is about 2.0 V. (b) How many kilograms of sodium are consumed when a 25 kW sodium–sulfur battery produces current for 32 min?

Experimental solid-oxide fuel cells that use butane (C4H10) as the fuel have been reported recently. These cells contain composite metal/metal oxide electrodes and a solid metal oxide electrolyte. The cell half-reactions are (c) How many grams of butane are required to produce a constant current of 10.5 A for 8.00 h? How many liters of gaseous butane at 20 °C and 815 mm Hg pressure are required?

The half-reactions that occur in ordinary alkaline batteries can be written as In 1999, researchers in Israel reported a new type of alkaline battery, called a 'super-iron' battery. This battery uses the same anode reaction as an ordinary alkaline battery but involves the reduction of FeO42- ion (from K2FeO4) to solid Fe(OH)3 at the cathode. (c) A super-iron battery should last longer than an ordinary alkaline battery of the same size and weight because its cathode can provide more charge per unit mass. Quan-titatively compare the number of coulombs of charge released by the reduction of 10.0 g K2FeO4 to Fe(OH)3 with the number of coulombs of charge released by the reduction 10.0 g of MnO2 to MnO(OH).