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chemistry for engineering students

Chemistry For Engineering Students 4th Edition Lawrence S. Brown, Tom Holme - Solutions

Using values from the table of standard reduction potentials, calculate the cell potentials of the following cells.(a) (b) (c) Fe(s) | Fe²+ (aq) || Hg2+ (aq) | Hg()
Use the Nernst equation to calculate the cell potentials of the following cells at 298 K. (a) 2 Ag+ (aq)(0.50 M) + Ni(s)→2 Ag(s) + Ni²+ (aq)(0.20 M) (b) Cu(s) + PtCl (aq) (0.10 M)→ Cu²+ (aq) (0.20 M) +PtCl (aq)(0.10 M) + 2 Cl(aq)(0.40 M) (aq)(0.30 M) + 2 AgCl(s) → (c) Pb(s) + SO4 PbSO4(s) +
We noted that a tin-plated steel can corrodes more quickly than an unplated steel can. In cases of galvanic corrosion, one cannot expect standard conditions. Suppose that you want to study the galvanic corrosion of tin-plated steel by constructing a cell with low concentrations of the ions. You
You are a chemical engineer in a firm that manufactures computer chips. A new accountant, who understands budgets but not chemistry, sends out the following memo:“Because of the high price of gold, the company should change from gold-plated pins on our computer chips to pins made of copper, which
Calculate the standard free energy change for the followingcells.(a) (b) (c) Ga(s) | Ga³+ (aq) || Ag+ (aq) | Ag(s)
Immediately after a person has his or her ears (or other body parts) pierced, a solid 14K gold post should be used to keep the hole open as it heals.(a) Explain why solid gold is preferred over other metals, such as steel.(b) Why do you think that a gold-plated steel post might not offer the same
In May 2000, a concrete pedestrian walkway collapsed in North Carolina, injuring more than 100 people. Investigation revealed that CaCl2 had been mixed into the grout that filled the holes around the steel reinforcing cables inside the concrete, resulting in corrosion of the cables, thus weakening
Calculate the standard free energy change for the following reactions using the standard cell potentials for the half-reactions that are involved. 2+ (a) Fe(s) + Hg₂+ (aq) → Fe²+ (aq) + 2 Hg(e) (b) Fe³+ (aq) + Ag(s) + Cl (aq) → Fe²+ (aq) + AgCl(s) (c) 2 MnO4 (aq) + 5 Zn(s) + 16 H3O+ (aq)
Suppose that you cannot find a table of standard reduction potentials. You remember that the standard reduction potential of Cu2+ + 2 e– → Cu(s) is 0.337 V. Given that ΔGf°(Cu2+) = 65.49 kJ mol–1 and that ΔGf°(Ni2+) = –45.6 kJ mol–1, determine the standard reduction potential of
Which of the following reactions is (are) spontaneous at standard conditions? 3+ 2+ (a) Zn(s) + 2 Fe³+ (aq) → Zn²+ (aq) + 2 Fe²+ (aq) (b) Cu(s) + 2 H+ (aq) → Cu²+ (aq) + H₂(g) (c) 2 Br (aq) + I₂(s)→ Br₂() +2 I¯(aq)
Consult a table of standard reduction potentials and determine which of the following reactions are spontaneous under standard electrochemical conditions. 2+ (a) Mn(s) + 2 H+ (aq) → H₂(g) + Mn²+ (aq) (b) 2 Al³+ (aq) + 3 H₂(g) → 2 Al(s) + 6 H* (aq) (c) 2 Cr(OH)3(s) + 6 F (aq) → 2 Cr(s) +
Use the potential of the galvanic cell, Co(s)Ι Co2+'IIPb2+IPb(s), to determine ΔGf°(Pb2+), given that ΔGf°(Co2+) = –54.4 kJ mol–1.
The equilibrium constant for a reaction is 3 × 10–15. (a) Without carrying out any calculation, discuss whether ΔG° for the reaction is positive or negative. (b) Calculate ΔG° for this reaction.
Use the standard reduction potentials for the reactions:to calculate the value of Ksp for silver chloride at 298 K. How does your answer compare with the value listed in Table 12.4?Table 12.4 AgCl(s) +eAg(s) + Cl (aq) and Ag+ (aq) + e→Ag(s)
Calculate the equilibrium constant for the following reactions using data from the standard reduction potential tables. (a) Cl₂(g) + 2 Br (aq) → Br₂(g) + 2 Cl¯(aq) (b) Ni(s) + 2 Ag+ (aq) →2 Ag(s) + Ni²+ (aq) (c) I₂(s) + Sn²+ (aq) → 2 I (aq) + Sn++ (aq)
Some calculators cannot display results of an antilog calculation if the power of 10 is greater than 99. This shortcoming can come into play for determining equilibrium constants of redox reactions, which are sometimes quite large. Solve the following expressions for K: (a) log K = 45.63,(b) log K
Hydrogen peroxide is often stored in the refrigerator to help keep it from decomposing according to the reaction:Use information from the standard reduction potentials to determine the equilibrium constant of this reaction. 2 H₂O₂(l) → 2 H₂O(l) + O₂(g)
Calculate the equilibrium constant for the redox reactions that could occur in the following situations and use that value to explain whether or not any reaction will be observed.(a) A piece of iron is placed in a 1.0 M solution of NiCl2(aq).(b) A copper wire is placed in a 1.0 M solution of
A magnesium bar with a mass of 6.0 kg is attached to a buried iron pipe to serve as a sacrificial anode. An average current of 0.020 A flows between the bar and the pipe. (a) What reaction takes place at the surface of the magnesium bar? (b) What reaction takes place at the surface of the iron
An engineer is assigned to design an electrochemical cell that will deliver a potential of exactly 1.52 V. Design and sketch a cell to provide this voltage, detailing the solutions, their concentrations, and the electrodes you will need. Write equations for all relevant reactions.
Zinc is used as a coating for galvanized steel, where it helps prevent corrosion. Explain why zinc would also make an acceptable sacrificial anode for a steel pipeline. Are these two uses related in terms of the science that gives rise to their utility?
Sacrificial anodes are sometimes connected to steel using a copper wire. If the anode is completely corroded away and not replaced, so that only the copper wire remains, what could happen where the copper and iron meet? Explain your answer.
What is the principal difference between a primary and a secondary cell?
Based on the chemistry that takes place, explain why an alkaline battery is called “alkaline.”
If you put a 9-volt battery in a smoke detector in your home or apartment, you are not installing a single galvanic cell. Explain how and why this is so.
If alkaline batteries were not alkaline but rather acidic (as in the older dry cell batteries), what extra difficulties could you envision with corrosion, based on reactions that are part of the table of standard reduction potentials?
What would happen to the voltage of an alkaline battery if the zinc were replaced by steel? Assume that the zinc reaction is simply ZnIZn2+ and that steel is iron.
The electrolyte solution in a zinc-air battery (Figure 13.16) is aqueous KOH. For a zinc-air battery to obtain O2 from the air, there are tiny openings in the battery. However, these openings also allow water vapor to escape and enter the battery as the humidity changes. The optimum relative
What product forms from the lead components of a lead storage battery? Why does mechanical shock (bumps) ultimately degrade the performance of the lead storage battery?
You are an electrical engineer investigating different button batteries for possible use in a design. You obtain the discharge curves shown in the graph for four different batteries under the same conditions and discharge load.(a) Write a paragraph in which you interpret curve (a) and curve (d) to
On the Internet, access the website of a major battery company, such as Rayovac, Duracell, or Eveready (Energizer). Search the site for a battery type not covered in this chapter. Find out all you can about the battery from engineering data or specification (spec) sheets. Print spec sheets that
What is the difference between active and passive electrolysis? Based on the common meanings of the words active and passive, what part of electrolysis is the focus of the name?
When aluminum is refined by electrolysis from its oxide ores, is the process used active or passive electrolysis? Explain your answer.
What complication arises in the electrolytic refining of aluminum because of the production of oxygen?
In an electroplating operation, the cell potential is sometimes 0 V. Why is a zero potential possible in electrolysis but not in a galvanic cell?
When copper wire is placed in a solution of silver nitrate, we say that the silver plates out on the copper, but we don’t call the process electroplating. Explain the difference.
In barrel plating, why is the barrel containing the small parts rotated?
When a coating is plated onto a metal, two different metals are in contact with each other. Why doesn’t galvanic corrosion occur at this interface?
Use the Internet to find electroplating companies that carry out silver plating. Popular impressions are that silver plating is mostly done for cosmetic reasons, making objects (like silverware) more attractive. Based on your Internet research, do you believe this popular impression accurately
Based on the reaction used for silver plating, suggest why there are environmental challenges associated with industrial plating companies. Use the Internet to find out how some electroplating companies address their responsibilities to protect the environment.
If a current of 15 A is run through an electrolysis cell for 2.0 hours, how many moles of electrons have moved?
Suppose somebody in a laboratory doesn’t quite turn off the current in an electrolysis cell so that 4.2 mA of current continues to flow. If the cell is then left untouched for exactly 3 weeks, how many moles of electrons have flowed through the cell in that time?
If a barrel plating run uses 200.0 A for exactly 6 hours for an electroplating application at 0.30 V, how many kilowatt- hours have been used in the run? If the voltage is 0.90 V, what is the power usage (in kWh)?
An electrical engineer is analyzing an electroplating run and wants to calculate the charge that has been used. She knows that the cell voltage is 0.25 V and that 10.3 kWh was expended. What was the charge? If the current of the apparatus is 3.0 A, how long was it running?
In a copper plating experiment in which copper metal is deposited from a copper(II) ion solution, the system is run for 2.6 hours at a current of 12.0 A. What mass of copper is deposited?
A metallurgist wants to gold-plate a thin sheet with the following dimensions: 1.5 in × 8.5 in × 0.0012 in. The gold plating must be 0.0020 in thick.(a) How many grams of gold (d = 19.3 g/cm3) are required?(b) How long will it take to plate the sheet from AuCN using a current of 7.00 A? (Assume
Tin-plated steel is used for “tin” cans. Suppose that in the production of sheets of tin-plated steel, a line at a factory operates at a current of 100.0 A for exactly 8 hours on a continuously fed sheet of unplated steel. If the electrolyte contains tin(II) ions, what is the total mass of tin
If a plating line that deposits nickel (from NiCl2 solutions) operates at a voltage of 0.40 V with a current of 400.0 A and a total mass of 49.0 kg of nickel is deposited, what is the minimum number of kWh consumed in this process?
Chrome is plated from solutions of chromium(III) ions. If a particular application requires 13.7 g of chromium in the coating and the run takes 90 minutes, what current was used?
When a lead storage battery is recharged by a current of 12.0 A for 15 minutes, what mass of PbSO4 is consumed?
A small part with a surface area of 2.62 cm2 is plated with a gold coating that is 5.00 × 10–4 mm thick. The density of gold is 19.32 g cm–3. What mass of gold is in this coating? If a barrel plating run has 5000 of these parts in a single barrel, how long would the run take if the current
An engineer is designing a mirror for an optical system. A piece of metal that measures 1.3 cm by 0.83 cm will have a coating of rhodium plated on its surface to serve as the mirror. The rhodium thickness will be 0.00030 mm, and the electrolyte contains Rh3+ ions. If the operating current of the
What two characteristics of lithium-ion batteries are responsible for their desirability in aerospace applications?
Looking at Figure 13.23, describe how the operation of a lithium-ion battery does not lead to a charge build up on one side of the battery or the other.Figure 13.23 Current Collector Cathode Separator Anode e =C = Co ● = Li =0 Current Collector
Explain why lithium-ion batteries tend to be relatively lightweight.
What characteristic of lithium ions makes it practical to build a semipermeable separator that allows them to flow through in a lithium-ion battery? Why would a sodium-ion battery be harder to design even if the oxidation–reduction reactions were similar?
Use the web to research how Boeing addressed the issue of battery fires in the Dreamliner, and write a short paragraph summarizing the company’s solution to the problem.
What is the role of a salt bridge in the construction of a galvanic cell?
Explain why a substance that is oxidized is called a reducing agent.
If the SHE was assigned a value of 3.00 V rather than 0.00 V, what would happen to all of the values listed in the table of standard reduction potentials?
A chemical engineering student is studying the effect of pH on the corrosion of iron. The following data are collected:Plot corrosion rate vs. pH. ( Label the x axis with decreasing pH.)(a) How would you describe the dependence of corrosion on pH?(b) When the pH goes below 3, bubbles appear in the
Explain why a large negative value for the standard reduction potential indicates a half-cell that is likely to undergo oxidation.
How is the relationship between maximum electrical work and cell potential used to determine the free energy change for electrochemical cells?
If a logarithmic scale had not been used for the graph of Figure 13.13, what would the plots look like?Figure 13.13 log K 120 100 80 60 40- 20- 0 0 0.5 1.0 Cell potential (V) 1.5 n=3 n=2 n=1 2.0
Would nickel make an acceptable sacrificial anode to protect steel? Explain your answer.
Battery manufacturers often assess batteries in terms of their specific energy (or energy capacity). The weight capacity of a battery is defined as q × V/mass. Why would a battery manufacturer be interested in this quantity?
Suppose you had a fresh battery and wanted to measure its weight capacity, as described in the previous problem. Devise and describe an experiment that you could carry out to make this measurement. Do you think performing your experiment on a single battery would yield reliable results?Data fro
Why is it easier to force an oxidation–reduction reaction to proceed in the nonspontaneous direction than it is to force an acid–base reaction in the nonspontaneous direction?
As the voltaic cell shown here runs, the blue solution gradually gets lighter in color and the gray solution gets darker.(a) What species is oxidized and what is reduced?(b) Which electrode is the anode and which is the cathode?(c) Which metal electrode gains mass?(d) In which direction do
In any electrochemical cell, reduction occurs at the cathode. Why does the cathode carry a negative charge, when electrolysis occurs, rather than the positive charge it carries in a galvanic cell?
Suppose that a student mistakenly thinks that copper is plated from solutions that contain copper(I) ions rather than copper(II) ions. How would this mistake affect the answer that student would get for the mass of copper plated out for a given time and current? (Is it too high, too low, and by
For a voltage-sensitive application, you are working on a battery that must have a working voltage of 0.85 V. The half-cells to be used have a standard cell potential of 0.97 V. What must be done to achieve the correct voltage? What information would you need to look up?
For a battery application, you need to get the largest possible voltage per cell. If voltage were the only concern, what chemical reactions would you choose? Use the Internet or your own background to speculate on the likely practical consequences of a choice driven by voltage alone.
An oxidation–reduction reaction using Sn(s) to remove N2O(g) from a reaction vessel has been proposed, and you need to find its equilibrium constant. You cannot find any thermodynamic information on one product of the reaction, NH3OH+(aq). How could you estimate the equilibrium constant of the
You are designing a system for a rather corrosive environment and are using an expensive alloy composed primarily of titanium. How would you choose a sacrificial anode to help protect this expensive component in your design? What information would you have to look up?
You need to use a gold-plated connector in a design to take advantage of the conductivity and corrosion resistance of gold. To justify this choice to the project director, you must devise a cost projection for several levels of plating. What parameters could be varied? What information would you
(a) What happens when a current is passed through a solution of dilute sulfuric acid to carry out electrolysis?(b) A 5.00-A current is passed through a dilute solution of sulfuric acid for 30.0 min. What mass of oxygen is produced?
A current is passed through a solution of copper(II) sulfate long enough to deposit 14.5 g of copper. What volume of oxygen is also produced if the gas is measured at 24°C and 0.958 atm of pressure?
Hydrazine, N2H4, has been proposed as the fuel in a fuel cell in which oxygen is the oxidizing agent. The reactions are(a) Which reaction occurs at the anode and which at the cathode?(b) What is the net cell reaction?(c) If the cell is to produce 0.50 A of current for 50.0 h, what mass in grams of
Given the equilibria:determine the equilibrium expression for the sum of the two reactions.Strategy Write the equilibrium expressions for the two reactions. Multiply them to obtain the equilibrium expression for the sum of the two reactions. Check your answer by adding the two reactions and
When hydrogen gas reacts with iodine gas at elevated temperatures, the following equilibrium is established:A student measured the equilibrium constant as 59.3 at 4008C. If one trial begins with a mixture that includes 0.050 M hydrogen and 0.050 M iodine, what will be the equilibrium concentrations
Write two examples of your own that illustrate the concept in the paragraph above.
The equilibrium constant for the reaction of chlorine gas with phosphorus trichloride to form phosphorus pentachloride is 33 at 250°C. If an experiment is initiated with concentrations of 0.050 M PCl3 and 0.015 M Cl2, what are the equilibrium concentrations of all three gases?Strategy The approach
In Chapter 11, we discussed several factors that can influence chemical kinetics. Use your understanding of those factors to offer an explanation as to why concrete hydration takes days to complete.
With what chemical in concrete does CO2 actually react during carbonation?
A student finds a piece of old concrete that has recently broken off from the curb alongside a road. Describe what she would expect to observe if she sprayed a solution containing phenolphthalein on all the surfaces of this piece of concrete.
Acetic acid, CH3COOH, has the peculiar property of being a retarding agent for concrete at low concentrations and an accelerator at high concentrations. A solution of acetic acid in equilibrium with hydrogen ions and acetate ions, CH3COO–, can be disturbed in several ways. Predict the change in
On your desk is a glass half-filled with water and a square glass plate to use as a cover for the glass.(a) How would you set up a dynamic equilibrium using the glass, water, and glass plate?(b) Once equilibrium is established in part (a), describe the processes that are occurring at the molecular
An equilibrium involving the carbonate and bicarbonate ions exists in natural waters:Assuming that the reactions in both directions are elementary processes:(a) Write rate expressions for the forward and reverse reactions.(b) Write an expression for the equilibrium constant based on the rates of
HCN is an important but potentially dangerous industrial chemical. It can be produced in several ways, including by the reactions shown below. Assuming that each system is initially at equilibrium, predict the direction in which the reaction will shift to respond to the indicated stress.(a) NH3(g)
What is the molar solubility of calcium phosphate, given that Ksp = 2.0 × 10–33?Assuming that the density of the saturated solution is 1.00 g/cm3, what is the solubility in grams of Ca3(PO4)2 per 100 grams of solvent?Strategy This problem asks us to find the equilibrium concentration of ions in
A small quantity of a soluble salt is placed in water. Equilibrium between dissolved and undissolved salt may or may not be attained. Explain.
In the following equilibrium in lake water, which of the inferences below can be drawn from the equation alone?(a) The rate of the forward reaction equals the rate of the reverse reaction.(b) The equilibrium concentrations of all species are equal.(c) Equilibrium was attained by starting with only
The Ksp of Ca3(PO4)2 is 2.0 × 10–33. Determine its molar solubility in 0.05 M (NH4)3PO4. Compare your answer to the molar solubility of Ca3(PO4)2 in water, which we calculated in Example Problem 12.11.Strategy (NH4)3PO4 is reasonably soluble in water, so [PO4 3–] in 0.05 M (NH4)3PO4 is 0.05 M.
Write equilibrium (mass action) expressions for each of the following reactions.(a) H2(g) + I2(g) ⇄ 2 HI(g)(b) 2 NO(g) + O2(g) ⇄ 2 NO2(g)(c) N2(g) + 3 H2(g) ⇄ 2 NH3(g)(d) CO(g) 1 NO2(g) N CO2(g) + NO(g)(e) 2 CO(g) + O2(g) ⇄ 2 CO2(g)
Write equilibrium (mass action) expressions for each of the following reactions.(a) 2 NOBr(g) ⇄ 2 NO(g) + Br2(g)(b) 4 HCl(g) + O2(g) ⇄ 2 H2O(g) + 2 Cl2(g)(c) SO2(g) + ½ O2(g) ⇄ SO3(g)(d) CH4(g) + 2 O2(g) ⇄ CO2(g) + 2 H2O(g)(e) C2H5OH(g) + 3 O2(g) ⇄ 2 CO2(g) + 3 H2O(g)
When dissolved in water, CH3COOH is called acetic acid. Write the equilibrium for its reaction in water and identify the conjugate acid2base pairs.Strategy Because acetic acid is behaving as a Brønsted–Lowry acid, it will require some species to accept a proton. Here the proton acceptor is
The Ka of acetic acid, CH3COOH, is 1.8 × 10–5. Calculate the pH of a 0.10 M acetic acid solution.Strategy We begin as usual, by setting up an equilibrium table and determining the concentrations of all species. Once we know the concentration of H3O+, we can find the pH.
What is the difference between homogeneous equilibrium and heterogeneous equilibrium?
What is the pH of 0.10 M NaOH?Strategy We know that NaOH is a strong base, so it will completely dissociate in solution. This gives us [OH–]. We can use the Kw relationship between [OH–] and [H3O+] to get [H3O+], which will then allow us to find the desired pH.

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