Hard Oxidation-Reduction Reactions Quiz
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Questions and Answers

What is the primary characteristic of an oxidation-reduction reaction?

  • One reactant is oxidized while another is reduced. (correct)
  • No change occurs in the reactants.
  • Both reactants are oxidized.
  • Only one reactant is oxidized.

    • In an oxidation-reduction reaction, the reducing agent is the species that is reduced.

    False

    What happens to the color of a silver nitrate solution when copper wire is added?

    The solution turns blue.

    In the reaction of copper with silver nitrate, copper is ______ and silver cations are ______.

    <p>oxidized, reduced</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Reducing agent = Species that donates electrons and is oxidized Oxidizing agent = Species that accepts electrons and is reduced Oxidation = Loss of electrons Reduction = Gain of electrons</p> Signup and view all the answers

    Which ion is formed when copper undergoes oxidation?

    <p>Cu2+</p> Signup and view all the answers

    In a galvanic cell, the chemical reaction that occurs is spontaneous and generates electric current.

    <p>True</p> Signup and view all the answers

    How many electrons does the silver cation Ag+ accept during the reaction with copper?

    <p>One</p> Signup and view all the answers

    What happens at the cathode during the reaction in a galvanic cell?

    <p>Cations are removed from the solution</p> Signup and view all the answers

    The electromotive force (EMF) is unrelated to the work obtainable from an electrochemical cell.

    <p>False</p> Signup and view all the answers

    What is the role of a salt bridge in a galvanic cell?

    <p>To close the circuit and prevent charge buildup.</p> Signup and view all the answers

    In galvanic corrosion, exposure of __ to air and moisture results in rapid corrosion.

    <p>tin-plated steel</p> Signup and view all the answers

    Match the types of corrosion with their descriptions:

    <p>Galvanic corrosion = Occurs between two different metals Uniform corrosion = Involves a single metal corroding uniformly Electrochemical corrosion = Involves electrons and redox reactions Localized corrosion = Occurs in small areas that corrode faster</p> Signup and view all the answers

    Which factor can facilitate uniform corrosion?

    <p>Presence of ionic salts</p> Signup and view all the answers

    Iron can corrode in the absence of moisture.

    <p>False</p> Signup and view all the answers

    What must occur at the anode of a galvanic cell?

    <p>Oxidation of metal.</p> Signup and view all the answers

    What occurs at the cathode in an electrochemical cell?

    <p>Reduction of species</p> Signup and view all the answers

    In an electrochemical cell, the anode is the negative terminal.

    <p>True</p> Signup and view all the answers

    What happens to the hydrogen ion (H+) when the SHE is connected to the cathode?

    <p>It is reduced to H2.</p> Signup and view all the answers

    Electrons flow from the anode to the ______.

    <p>cathode</p> Signup and view all the answers

    Match the following terms with their correct description:

    <p>Anode = Site of oxidation Cathode = Site of reduction Standard Reduction Potential = Measure of tendency to gain electrons SHE = Standard Hydrogen Electrode</p> Signup and view all the answers

    What does a positive standard reduction potential indicate?

    <p>The SHE is located at the anode</p> Signup and view all the answers

    Reversing the leads of the voltmeter will change the flow of current in the circuit.

    <p>False</p> Signup and view all the answers

    What happens to the sign of half-reaction potential when it is reversed for oxidation?

    <p>The sign of the cell potential must be changed.</p> Signup and view all the answers

    What does a large positive value for the standard reduction potential indicate?

    <p>The substance is readily reduced.</p> Signup and view all the answers

    The half-reaction with the more negative reduction potential serves as the cathode in a galvanic cell.

    <p>False</p> Signup and view all the answers

    What is the standard reduction potential for a galvanic cell composed of copper and iron that yields a potential of 0.462 V?

    <p>0.462 V</p> Signup and view all the answers

    The standard reduction potential for the anode is designated as E°______.

    <p>ox</p> Signup and view all the answers

    In a galvanic cell, which equation is used to calculate cell potential under nonstandard conditions?

    <p>Nernst equation</p> Signup and view all the answers

    Corrosion is a spontaneous process that has a positive Gibbs free energy change.

    <p>False</p> Signup and view all the answers

    What is the value of Faraday's constant in J V-1 mol-1?

    <p>96485 J V-1 mol-1</p> Signup and view all the answers

    What type of corrosion occurs evenly over a large portion of a metal's surface area?

    <p>Uniform corrosion</p> Signup and view all the answers

    Aluminum tends to corrode more than iron, but corrosion of aluminum is problematic.

    <p>False</p> Signup and view all the answers

    What are oxidation-reduction reactions commonly referred to as?

    <p>Redox reactions</p> Signup and view all the answers

    Crevice corrosion occurs when two pieces of metal touch each other, leaving a small ______ between the metals.

    <p>gap</p> Signup and view all the answers

    Match the type of corrosion with its description:

    <p>Uniform corrosion = Even degradation over a large surface area Galvanic corrosion = Occurs between two different metals in electrolyte Crevice corrosion = Happens where there is a small gap between metals Pitting corrosion = Localized corrosion leading to small holes or pits</p> Signup and view all the answers

    The corrosion product of aluminum forms a protective layer called:

    <p>Aluminum oxide</p> Signup and view all the answers

    Galvanic corrosion can occur between the same type of metal.

    <p>False</p> Signup and view all the answers

    What is one technique for preventing corrosion?

    <p>Galvanization</p> Signup and view all the answers

    What is one major goal of the design of the Boeing Dreamliner?

    <p>Minimize weight</p> Signup and view all the answers

    High temperatures improve the lifespan of lithium-ion batteries.

    <p>False</p> Signup and view all the answers

    What material is used as the anode in lithium-ion batteries?

    <p>Graphite</p> Signup and view all the answers

    Lithium-ion batteries have high energy density because Li+/Li has one of the largest standard reduction ______.

    <p>potentials</p> Signup and view all the answers

    Match the following components of the lithium-ion battery with their roles:

    <p>Anode = Graphite with intercalated lithium Cathode = Cobalt oxide with lithium Lithium = Component that provides high energy capacity Carbon = Material contributing to low weight</p> Signup and view all the answers

    What occurs during the oxidation of copper in the reaction with silver nitrate?

    <p>Copper loses two electrons</p> Signup and view all the answers

    The species that gets oxidized in a redox reaction is called the oxidizing agent.

    <p>False</p> Signup and view all the answers

    What is the color change observed when copper wire is placed in a silver nitrate solution?

    <p>The solution turns blue.</p> Signup and view all the answers

    In a galvanic cell, the process that generates electric current is a __________ reaction.

    <p>spontaneous</p> Signup and view all the answers

    During the redox reaction between copper and silver nitrate, which statement is true?

    <p>Cu is oxidized and serves as the reducing agent.</p> Signup and view all the answers

    Match the following terms to the correct definitions:

    <p>Reducing agent = Species that is oxidized Oxidizing agent = Species that is reduced Galvanic cell = Spontaneous chemical reaction that generates electric current Half-reaction = Shows oxidation or reduction separately</p> Signup and view all the answers

    In a redox reaction, oxidation and reduction can occur independently.

    <p>False</p> Signup and view all the answers

    What is the unit of current measured in an electric circuit?

    <p>Ampere</p> Signup and view all the answers

    What is formed on the surface of the copper wire when it reacts with silver nitrate?

    <p>Silver metal</p> Signup and view all the answers

    Electroplating is primarily used to enhance the conductivity of metals.

    <p>False</p> Signup and view all the answers

    What constant is used to calculate the number of moles of electrons in electroplating?

    <p>Faraday's constant</p> Signup and view all the answers

    The SI unit for power is the ______.

    <p>watt</p> Signup and view all the answers

    Match the following processes with their respective electrical parameters:

    <p>Current = Measured in amperes Charge = Measured in coulombs Power = Measured in watts Voltage = Measured in volts</p> Signup and view all the answers

    If a current of 2.50 x 10^3 A flows for 5.00 minutes, what is the charge?

    <p>75000 C</p> Signup and view all the answers

    Kilowatt-hours is a measure of electrical power consumption over time.

    <p>True</p> Signup and view all the answers

    What is the energy cost determined by if a company uses 0.15 V and 15.0 A for plating?

    <p>$0.0500 per kWh</p> Signup and view all the answers

    What happens at the cathode of an electrochemical cell?

    <p>Reduction occurs</p> Signup and view all the answers

    When the standard reduction potential is positive, the half-reaction proceeds as an oxidation.

    <p>False</p> Signup and view all the answers

    Describe the direction of electron flow in a galvanic cell.

    <p>From the anode to the cathode.</p> Signup and view all the answers

    In a galvanic cell, the half-reaction that is ______ is one that appears as a reduction in the standard reduction potential table.

    <p>oxidation</p> Signup and view all the answers

    If the SHE is connected to the positive terminal of a voltmeter, what does a negative potential indicate?

    <p>The SHE is the anode.</p> Signup and view all the answers

    Reversing the leads of the voltmeter influences the flow of current in the circuit.

    <p>False</p> Signup and view all the answers

    What does a large positive value of standard reduction potential indicate about the half-reaction?

    <p>It has a strong tendency to gain electrons and undergo reduction.</p> Signup and view all the answers

    What happens to charged ions at the cathode during electrochemical reactions?

    <p>Reduction occurs</p> Signup and view all the answers

    The presence of a salt bridge is necessary for charge buildup at the electrodes in a galvanic cell.

    <p>True</p> Signup and view all the answers

    What is the potential for electrical work produced by an electrochemical cell called?

    <p>Electromotive force (EMF)</p> Signup and view all the answers

    In uniform corrosion of iron, iron is oxidized, and oxygen from the air is ______.

    <p>reduced</p> Signup and view all the answers

    Which of the following components speeds up the corrosion reaction in iron?

    <p>Ionic salts</p> Signup and view all the answers

    Match the types of corrosion to their examples:

    <p>Galvanic corrosion = Occurs between metals in contact Uniform corrosion = Even corrosion over a surface Pitting corrosion = Localized corrosion that creates small pits Crevice corrosion = Occurs in confined spaces between two surfaces</p> Signup and view all the answers

    What is created when the tin coating of a tin-plated steel can is scratched?

    <p>Rapid corrosion of iron</p> Signup and view all the answers

    The equation for the maximum work obtainable from an electrochemical cell is expressed as ______.

    <p>w = qE</p> Signup and view all the answers

    What is a major reason for the Boeing Dreamliner requiring higher electrical power than conventional aircraft?

    <p>Replacing the hydraulic system with an all-electronic alternative</p> Signup and view all the answers

    Lithium-ion batteries are known for their high energy capacity and high weight.

    <p>False</p> Signup and view all the answers

    What materials make up the anode and cathode of lithium-ion batteries?

    <p>The anode is made of graphite and the cathode is made of cobalt oxide.</p> Signup and view all the answers

    Lithium-ion batteries degrade quickly at ______ temperatures.

    <p>high</p> Signup and view all the answers

    Match the following components of lithium-ion batteries with their roles:

    <p>Anode = Graphite containing lithium Cathode = Cobalt oxide containing lithium Lithium ions = Charge carriers Electrolyte = Conducts ions between anode and cathode</p> Signup and view all the answers

    What primary process does electrolysis provide in refining aluminum?

    <p>Separating aluminum from its oxide</p> Signup and view all the answers

    The anode becomes the negative electrode during electrolysis.

    <p>False</p> Signup and view all the answers

    What type of coating is applied during electroplating?

    <p>A thin coat of metal</p> Signup and view all the answers

    In the Hall-Heroult process, aluminum is separated from ______.

    <p>Al2O3</p> Signup and view all the answers

    What is a common application of silver plating in electroplating?

    <p>Improving conductivity</p> Signup and view all the answers

    Barrel plating is typically used to coat large components.

    <p>False</p> Signup and view all the answers

    What is the purpose of controlling the flow of electrons in electroplating?

    <p>To limit the amount of material deposited</p> Signup and view all the answers

    Which type of corrosion occurs when two different metals are in contact in the presence of an electrolyte?

    <p>Galvanic corrosion</p> Signup and view all the answers

    Aluminum oxide forms a protective layer that helps prevent further corrosion of aluminum.

    <p>True</p> Signup and view all the answers

    What is the primary difference between galvanic and electrolytic cells?

    <p>Galvanic cells generate electric current from spontaneous chemical reactions, while electrolytic cells require an external voltage to drive non-spontaneous reactions.</p> Signup and view all the answers

    Corrosion is the degradation of metals through chemical reactions with the __________.

    <p>environment</p> Signup and view all the answers

    What is a common technique for preventing corrosion of metals?

    <p>Coating the metal with paint</p> Signup and view all the answers

    What chemical reaction occurs in a redox process?

    <p>A transfer of electrons between reactants, with one species being oxidized and another being reduced.</p> Signup and view all the answers

    The corrosion product of iron forms a protective layer that prevents further corrosion.

    <p>False</p> Signup and view all the answers

    What happens to the sign of the measured voltage when the poles of a battery are reversed with respect to a voltmeter?

    <p>The measured voltage changes sign</p> Signup and view all the answers

    The standard hydrogen electrode (SHE) is assigned a potential of exactly one volt.

    <p>False</p> Signup and view all the answers

    What is the function of the platinum wire or foil in the standard hydrogen electrode?

    <p>It serves as the electrode.</p> Signup and view all the answers

    The cell potential of a copper/silver cell when measured was __________ V.

    <p>0.462</p> Signup and view all the answers

    Match the electrochemical cell components with their functions:

    <p>Anode = Site of oxidation Cathode = Site of reduction Voltmeter = Measures electric potential Half-cell = Contains the reactants for half-reactions</p> Signup and view all the answers

    When connecting the copper half-cell to a reducing iron(III)/iron(II) half-cell, what cell potential is measured?

    <p>0.434 V</p> Signup and view all the answers

    The half-cell notation for the standard hydrogen electrode is Pt(s) | H2(g, 1 atm) | H+ (1 M).

    <p>True</p> Signup and view all the answers

    The behavior of cell potentials is akin to __________ functions.

    <p>state</p> Signup and view all the answers

    What happens at the cathode in a galvanic cell?

    <p>Reduction occurs.</p> Signup and view all the answers

    A positive cell potential indicates that the standard hydrogen electrode (SHE) is acting as the anode.

    <p>False</p> Signup and view all the answers

    What does a negative standard reduction potential indicate about the half-reaction?

    <p>It indicates that the half-reaction proceeds as oxidation.</p> Signup and view all the answers

    In a galvanic cell, the direction of electron flow is from the ______ to the ______.

    <p>anode, cathode</p> Signup and view all the answers

    Match the following terms to their correct meanings:

    <p>Anode = Site of oxidation Cathode = Site of reduction Standard Reduction Potential = Measured with respect to SHE Galvanic cell = Spontaneous electrochemical reaction</p> Signup and view all the answers

    What happens when the leads of the voltmeter are reversed?

    <p>It changes the sign of the potential reading.</p> Signup and view all the answers

    In a standard reduction potential table, all half-reactions are listed as reductions.

    <p>True</p> Signup and view all the answers

    What indicates that H2 gas is being reduced?

    <p>When the SHE is connected to the cathode with a positive potential reading.</p> Signup and view all the answers

    What is the primary component of a lithium battery that serves as the anode?

    <p>Lithium</p> Signup and view all the answers

    A primary cell can be recharged multiple times.

    <p>False</p> Signup and view all the answers

    What occurs at the anode of an alkaline battery?

    <p>Oxidation</p> Signup and view all the answers

    In a zinc-air battery, zinc acts as the ______.

    <p>anode</p> Signup and view all the answers

    Which of the following statements regarding the equilibrium constant and cell potential is true?

    <p>The equilibrium constant increases as cell potential increases.</p> Signup and view all the answers

    Galvanic corrosion cannot occur between different types of metals.

    <p>False</p> Signup and view all the answers

    Match the following types of primary cells with their characteristics:

    <p>Alkaline battery = Has zinc as anode, manganese(IV) oxide as cathode Lithium battery = Used in medical devices like pacemakers Zinc-air battery = Zinc as anode, oxygen at cathode Silver oxide battery = Common in watches and cameras</p> Signup and view all the answers

    What is the role of Faraday's constant in electrochemical reactions?

    <p>It relates the amount of electric charge to the amount of substance reacted.</p> Signup and view all the answers

    What reactant does a zinc-air battery use from the environment?

    <p>Oxygen</p> Signup and view all the answers

    Nickel-metal-hydride batteries are considered primary cells.

    <p>False</p> Signup and view all the answers

    What type of acid is used in lead-acid storage batteries?

    <p>sulfuric acid</p> Signup and view all the answers

    In a fuel cell, hydrogen is ______ at the anode.

    <p>oxidized</p> Signup and view all the answers

    What is one major limitation affecting the performance of batteries?

    <p>Corrosion</p> Signup and view all the answers

    Match the type of electrolysis with its characteristics:

    <p>Passive electrolysis = Electrodes are chemically inert Active electrolysis = Electrodes participate in the reaction</p> Signup and view all the answers

    Lithium-ion batteries function more effectively at high temperatures.

    <p>False</p> Signup and view all the answers

    In electrolysis, the cathode is where oxidation occurs.

    <p>False</p> Signup and view all the answers

    What is the primary reason for using lithium-ion batteries in the Boeing Dreamliner?

    <p>They provide high energy capacity and low weight.</p> Signup and view all the answers

    The anode in a lithium-ion battery is primarily made up of ______.

    <p>graphite</p> Signup and view all the answers

    A fuel cell continuously supplies reactants and removes ______.

    <p>products</p> Signup and view all the answers

    Match the following factors with their impact on lithium-ion battery performance:

    <p>High temperatures = Degrade battery quickly Low weight = Improves fuel efficiency High energy capacity = Supports electrical power demands Graphite anode = Facilitates electron movement</p> Signup and view all the answers

    What role does the salt bridge play in a galvanic cell?

    <p>It allows ion migration to maintain charge neutrality.</p> Signup and view all the answers

    The electrode where reduction occurs is known as the anode.

    <p>False</p> Signup and view all the answers

    What is the measured voltage potential for the described copper-silver galvanic cell?

    <p>0.46 V</p> Signup and view all the answers

    In galvanic cells, oxidation occurs at the ______.

    <p>anode</p> Signup and view all the answers

    Match the following components of a galvanic cell to their functions:

    <p>Anode = Electrode where oxidation occurs Cathode = Electrode where reduction occurs Salt Bridge = Maintains charge neutrality Half-cell = Contains metal and electrolyte solution</p> Signup and view all the answers

    Which ion migrates into the Ag+ solution in a galvanic cell using NH4Cl salt bridge?

    <p>NH4+</p> Signup and view all the answers

    A metal wire can be used in a galvanic cell to transport ions.

    <p>False</p> Signup and view all the answers

    What is the general form of cell notation for a galvanic cell?

    <p>Anode | Anion || Cation | Cathode</p> Signup and view all the answers

    What is the significance of the Standard Hydrogen Electrode (SHE)?

    <p>It provides a reference point for measuring cell potentials.</p> Signup and view all the answers

    Reversing the polarity of a battery affects the electrochemical reaction in the battery.

    <p>False</p> Signup and view all the answers

    What potential is assigned to the Standard Hydrogen Electrode (SHE)?

    <p>0 volts</p> Signup and view all the answers

    At the anode of a galvanic cell, __________ occurs.

    <p>oxidation</p> Signup and view all the answers

    Match the half-cell notations to their characteristics:

    <p>Pt(s) | H2(g, 1 atm) | H+ (1 M) = Standard Hydrogen Electrode Cu2+ | Cu(s) = Copper half-cell Ag+ | Ag(s) = Silver half-cell Fe3+ | Fe2+ = Iron(III)/iron(II) half-cell</p> Signup and view all the answers

    The behavior of cell potentials is similar to state functions.

    <p>True</p> Signup and view all the answers

    The electrochemical reaction that occurs at the __________ results in a positive terminal on a voltmeter.

    <p>cathode</p> Signup and view all the answers

    What happens to the charge on the cathode as reduction occurs during an electrochemical reaction?

    <p>The charge becomes positive</p> Signup and view all the answers

    A salt bridge in a galvanic cell is necessary to prevent local charge build-up and maintain the circuit.

    <p>True</p> Signup and view all the answers

    What is the potential called that indicates the maximum work obtainable from an electrochemical cell?

    <p>Electromotive force (EMF)</p> Signup and view all the answers

    What role does water play in the corrosion of iron?

    <p>It enhances ion mobility</p> Signup and view all the answers

    The buildup of charge on an electrode does not affect the performance of an electrochemical cell.

    <p>False</p> Signup and view all the answers

    Iron is oxidized, and oxygen from the air is _____ during the corrosion process.

    <p>reduced</p> Signup and view all the answers

    What is the unit of current in an electric circuit?

    <p>Ampere</p> Signup and view all the answers

    Galvanic corrosion can be prevented through electroplating.

    <p>True</p> Signup and view all the answers

    What is Faraday's constant?

    <p>96485 C mol-1</p> Signup and view all the answers

    Match the following concepts with their definitions:

    <p>Coulomb = Unit of electric charge Ampere = Unit of electric current Volt = Unit of electric potential Watt = Unit of power</p> Signup and view all the answers

    How is energy consumption usually measured by electrical utilities?

    <p>Kilowatt-hours</p> Signup and view all the answers

    Electrolysis can be used to calculate the mass of material plated based on current and time.

    <p>True</p> Signup and view all the answers

    If a current of 2.30 A operates for 15.0 minutes, what is the first step in calculating the mass of gold deposited?

    <p>Determine the total charge passed through the cell.</p> Signup and view all the answers

    When the SHE is connected to the positive terminal, it indicates that the SHE is acting as the cathode.

    <p>True</p> Signup and view all the answers

    What is indicated by a negative standard reduction potential?

    <p>Oxidation occurs.</p> Signup and view all the answers

    In a galvanic cell, electrons flow from the ______ to the cathode.

    <p>anode</p> Signup and view all the answers

    What happens when the leads of the voltmeter are reversed in a galvanic cell?

    <p>The sign of the voltage reading changes</p> Signup and view all the answers

    All half-reactions in electrochemistry tables are written for oxidation.

    <p>False</p> Signup and view all the answers

    What does a positive standard reduction potential mean for a half-reaction?

    <p>The half-reaction proceeds as written (reduction occurs).</p> Signup and view all the answers

    What is the primary chemistry constituent of an alkaline battery?

    <p>Zinc electrode and manganese(IV) oxide</p> Signup and view all the answers

    Zinc-air batteries have oxygen acting as the anode during the reaction.

    <p>False</p> Signup and view all the answers

    What happens to the equilibrium constant as the cell potential increases?

    <p>The equilibrium constant increases.</p> Signup and view all the answers

    Lithium batteries provide a stable current and electrical potential for long periods because they react with ______ ions.

    <p>lithium</p> Signup and view all the answers

    Match the following batteries with their descriptions:

    <p>Alkaline Battery = Single-use battery with zinc and manganese(IV) oxide Lithium Battery = Long-lasting, stable current for medical devices Zinc-Air Battery = Uses zinc as the anode and reacts with oxygen Primary Cells = Batteries that cannot be recharged</p> Signup and view all the answers

    What statement best describes primary cells?

    <p>They cannot be recharged and are used once.</p> Signup and view all the answers

    The cell potential can be used to calculate the standard free energy change for an electrochemical reaction.

    <p>True</p> Signup and view all the answers

    What component is used in the anode of lithium batteries?

    <p>Lithium</p> Signup and view all the answers

    Which type of corrosion occurs when two different metals contact each other in the presence of an electrolyte?

    <p>Galvanic corrosion</p> Signup and view all the answers

    Iron tends to corrode less aggressively than aluminum.

    <p>False</p> Signup and view all the answers

    Name one common technique for preventing corrosion.

    <p>Galvanization</p> Signup and view all the answers

    Corrosion occurs as a result of chemical reactions between metals and the __________.

    <p>environment</p> Signup and view all the answers

    Electrolytic cells operate on spontaneous chemical processes.

    <p>False</p> Signup and view all the answers

    What is the corrosion product of aluminum that forms a protective layer?

    <p>Aluminum oxide</p> Signup and view all the answers

    What is one of the primary materials used in the anode of lithium-ion batteries?

    <p>Graphite</p> Signup and view all the answers

    Lithium-ion batteries perform well in high temperatures.

    <p>False</p> Signup and view all the answers

    Why was the Boeing Dreamliner designed to require lithium-ion batteries?

    <p>To achieve higher electrical power and minimize weight for increased fuel efficiency.</p> Signup and view all the answers

    The cathode in lithium-ion batteries is primarily composed of ________ oxide.

    <p>cobalt</p> Signup and view all the answers

    Match the reasons for the high energy density of lithium-ion batteries with the corresponding explanations:

    <p>Li+/Li has a high standard reduction potential = This allows for a strong driving force in reactions Both lithium and carbon are light = Helps to minimize the overall weight of the battery</p> Signup and view all the answers

    What happens to the charges at the electrodes without a salt bridge?

    <p>Local charges build up and inhibit electrode reactions.</p> Signup and view all the answers

    Galvanic corrosion can occur when two metals are in contact with each other.

    <p>True</p> Signup and view all the answers

    What is the role of water in the corrosion of iron?

    <p>Ion mobility</p> Signup and view all the answers

    The potential for electrical work in an electrochemical cell is called ______.

    <p>electromotive force</p> Signup and view all the answers

    Match the types of corrosion with their characteristics:

    <p>Galvanic Corrosion = Occurs between dissimilar metals in contact Uniform Corrosion = Occurs evenly across a metal's surface Pitting Corrosion = Localized corrosion that leads to holes Crevice Corrosion = Occurs in small spaces between metals</p> Signup and view all the answers

    Which equation represents the maximum work obtainable from an electrochemical cell?

    <p>w = q E</p> Signup and view all the answers

    Cations are removed from solution at the anode during a redox reaction.

    <p>False</p> Signup and view all the answers

    The oxidation half-reaction equilibrium is established when metals are in contact with a __________.

    <p>solution</p> Signup and view all the answers

    What flows through a salt bridge to maintain charge neutrality in a galvanic cell?

    <p>Cations or anions</p> Signup and view all the answers

    Current in a galvanic cell flows through a metal wire connecting the half-cells.

    <p>False</p> Signup and view all the answers

    What is the role of the anode in a galvanic cell?

    <p>The anode is where oxidation occurs.</p> Signup and view all the answers

    The voltage potential measured for the copper and silver galvanic cell is ______ V.

    <p>0.46</p> Signup and view all the answers

    Which ion flows into the Ag+ beaker from the salt bridge during operation?

    <p>NH4+</p> Signup and view all the answers

    The cathode is written on the left side of cell notation.

    <p>False</p> Signup and view all the answers

    Before the half-cells are connected, a small buildup of ______ occurs at the interface between the electrode and the electrolyte.

    <p>charge</p> Signup and view all the answers

    The primary unit used to measure electrical energy consumption is the joule.

    <p>False</p> Signup and view all the answers

    If a current of 3 A flows for 10 minutes, what is the total charge that has passed through the circuit?

    <p>1800 coulombs</p> Signup and view all the answers

    The process of depositing gold from Au+ involves electro_____.

    <p>plating</p> Signup and view all the answers

    How much energy is required to run an electrolytic bath at 15.0 A for 2 hours?

    <p>7.2 kWh</p> Signup and view all the answers

    What is Faraday’s constant, and what does it represent?

    <p>96,485 C mol-1, it represents the charge of one mole of electrons.</p> Signup and view all the answers

    To deposit a desired mass of plated material, one must know the current, time, stoichiometry, and the number of _____ required to reduce a metal cation.

    <p>electrons</p> Signup and view all the answers

    When the SHE is connected to the positive terminal, a negative potential indicates that it is the anode.

    <p>False</p> Signup and view all the answers

    At the cathode, _____ ions are reduced to form hydrogen gas (H2).

    <p>hydrogen</p> Signup and view all the answers

    What happens to the sign of the potential when a half-reaction is reversed from reduction to oxidation?

    <p>It becomes negative</p> Signup and view all the answers

    Electrons flow from the cathode to the anode in a galvanic cell.

    <p>False</p> Signup and view all the answers

    What effect does reversing the leads of the voltmeter have on the flow of current?

    <p>It changes the sign of the reading but does not influence the flow of current.</p> Signup and view all the answers

    Study Notes

    Chapter Objectives

    • Describe at least three types of corrosion and identify chemical reactions responsible for corrosion.
    • Define oxidation and reduction.
    • Write and balance half-reactions for simple redox processes.
    • Describe the differences between galvanic and electrolytic cells.
    • Use standard reduction potentials to calculate cell potentials under both standard and nonstandard conditions.
    • Use standard reduction potentials to predict the spontaneous direction of a redox reaction.
    • Calculate the amount of metal plated, the amount of current needed, or the time required for an electrolysis process.
    • Distinguish between primary and secondary batteries.
    • Describe the chemistry of some common battery types and explain why each type of battery is suitable for a particular application.
    • Describe at least three common techniques for preventing corrosion.

    Corrosion

    • Corrosion is the degradation of metals by chemical reactions with the environment.
    • Uniform corrosion occurs evenly over a large portion of the surface area of a metal.
    • Galvanic corrosion occurs when two different metals contact each other in the presence of an appropriate electrolyte.
    • Crevice corrosion occurs when two pieces of metal touch each other, leaving a small gap or crevice between the metals.
    • Different metals corrode differently.
    • Aluminum has a greater tendency to corrode than iron, but corrosion of aluminum is not problematic compared to iron.
    • The aluminum oxide corrosion product forms a protective layer on the surface of aluminum metal.
    • The iron oxide corrosion product flakes off the surface of iron, exposing fresh iron to corrosion.
    • Corrosion occurs in a variety of forms. The chain shows uniform corrosion. The grill cover shows crevice corrosion where the handle is attached.

    Oxidation-Reduction Reactions and Galvanic Cells

    • Special conditions must be present before iron reacts with oxygen to form iron(III) oxide.
    • Rust formation is a slow process, so the basics of electrochemistry must be investigated using more easily observed reactions.
    • Reactions that transfer electrons between reactants are known as oxidation-reduction or redox reactions.
    • Oxidation is the loss of electrons from some chemical species.
    • Reduction is the gain of electrons to some chemical species.
    • For an oxidation-reduction reaction to occur, one reactant must be oxidized and one reactant must be reduced.
    • Oxidation cannot occur without reduction.
    • When copper wire is placed in a silver nitrate solution, a redox reaction occurs.
    • A reaction is observed to occur because the solution changes color and crystals form on the surface of the copper wire.
    • The solution's blue color is indicative of Cu²⁺ ions in solution.
    • Cu²⁺ is formed when a copper atom loses two electrons.
    • The copper metal is oxidized.
    • The crystals forming on the surface of the copper wire are silver metal.
    • Silver is formed when a silver cation gains an electron.
    • The silver cation is reduced.
    • For the reaction between silver cation and copper metal, two half-reactions are written.
    • One for the oxidation of copper and one for the reduction of silver.
    • Neither half-reaction can occur without the other.
    • The half-reactions as written indicate that Ag⁺ only accepts one electron whereas Cu loses two electrons.
    • The electron transfer must balance, so the reduction half-reaction is multiplied by 2.
    • Add the two half-reactions together, the electrons cancel out, leaving the net ionic equation for the redox reaction.
    • The species undergoing oxidation is referred to as a reducing agent.
    • The Cu was oxidized and is the reducing agent.
    • The Cu facilitated the reduction of Ag⁺ by losing electrons.
    • The species undergoing reduction is referred to as an oxidizing agent.
    • The Ag⁺ was reduced and is the oxidizing agent.
    • The Ag⁺ facilitated the oxidation of Cu by gaining electrons.

    Building a Galvanic Cell

    • A galvanic cell is any electrochemical cell in which a spontaneous chemical reaction can be used to generate an electric current.
    • The name electrochemistry comes from the observation of electric currents in galvanic cells.
    • To harness electricity from a galvanic cell, each half-reaction is prepared separately in half-cells.
    • Cu metal immersed in Cu²⁺ solution is one half-cell.
    • Ag metal immersed in Ag⁺ solution is the second half-cell.
    • A salt bridge is crucial to a galvanic cell. The salt bridge allows ions to flow between each half-cell, completing the circuit.
    • Current flows by the migration of ions in solution.
    • To transfer current between the half-cells, a salt bridge is used.
    • The salt bridge contains a strong electrolyte that allows either cations or anions to migrate into the solution where they are needed to maintain charge neutrality.
    • A metal wire cannot transport ions and cannot be used.
    • For a salt bridge composed of NH₄Cl: NH₄⁺ will flow into the Ag⁺ beaker to offset the removal of Ag⁺ from solution. Cl⁻ will flow into the Cu²⁺ beaker to offset the production of Cu²⁺ in solution.
    • The circuit is completed by connecting wires to each metal strip.
    • A voltage potential of 0.46 V will be measured for the described cell.

    Terminology for Galvanic Cells

    • Electrodes are the electrically conducting sites at which either oxidation or reduction occurs.
    • Oxidation occurs at the anode.
    • Reduction occurs at the cathode.
    • Cell notation - a shorthand notation for the specific chemistry of an electrochemical cell.
    • Cell notation lists the metals and ions involved in the reaction.
    • A vertical line, |, denotes a phase boundary.
    • A double vertical line, ||, denotes a salt bridge.
    • The anode is written on the left, the cathode on the right.
    • General form of cell notation anode | anode electrolyte || cathode electrolyte | cathode

    Standard Reduction Potentials

    • To compare the oxidation-reduction trends of species used in electrochemistry, all half-cell potentials are written as reductions.
    • A table of standard reduction potentials lists the potential of any half-reaction when connected to a SHE.
    • All materials are 1 M for aqueous species and 1 atm partial pressure for gases.
    • Although the half-reactions are listed as reductions in the table, one half-reaction in any electrochemical cell must be an oxidation and, therefore, reversed from what appears in the table.
    • The cell potential sign must be changed when writing the half-reaction as an oxidation.
    • Some half-reactions have positive potentials, whereas others have negative potentials.
    • All potentials are measured with a SHE connected to the positive terminal.
    • If the voltage is positive, the SHE is the anode, the oxidation site.
    • A positive standard reduction potential means the half-reaction proceeds as written (reduction occurs).
    • If the voltage is negative, the SHE is the cathode, the reduction site.
    • A negative standard reduction potential means the half-reaction proceeds as an oxidation.
    • The tendency for the chemicals involved in a half-reaction to be an oxidation or reduction depends on the value of the reduction potential.
    • A large, positive value for the standard reduction potential implies the substance is reduced readily and a good oxidizing agent.
    • A large, negative value for the standard reduction potential implies the substance is oxidized readily and a good reducing agent.
    • For a galvanic cell, the half-reaction with the more positive reduction potential will be the cathode. The half-reaction with the more negative reduction potential will be the anode.
    • The standard reduction potential for any pair of half-reactions, E°cell, is calculated from the standard reduction potentials for the cathode and anode.
    • E°cell = E°red - E°ox

    Example Problem 13.1

    • Use standard reduction potentials to identify the anode and cathode and determine the cell potential for a galvanic cell composed of copper and iron. Assume standard conditions.
    • Confirm that the potential of the following galvanic cell is 0.462 V: Cu(s) | Cu²⁺ (1 M) || Ag⁺ (1 M) | Ag(s)

    Nonstandard Conditions

    • The cell potential at nonstandard conditions is calculated using the Nernst equation.
    • E=E° - (RT/nF) lnQ
    • Q is the reaction quotient, F is the Faraday constant, and n is the number of electrons transferred in the reaction.
    • F = 96,485 J V⁻¹ mol⁻¹ or 96,485 C mol⁻¹

    Example Problem 13.2

    • Assume that you have a cell that has an iron(II) concentration of 0.015 M and an H⁺ concentration of 1.0 × 10⁻³ M. The cell temperature is 38°C, and the pressure of hydrogen gas is maintained at 0.04 atm. What would the cell potential be under these conditions?

    Cell Potentials and Free Energy

    • Corrosion is a spontaneous process and has a negative Gibbs free energy change.
    • The Gibbs free energy change for an electrochemical reaction can be calculated from the standard reduction potential.
    • ΔG° = -nFE°
    • n is the number of electrons transferred and F is Faraday's constant

    Example Problem 13.3

    • Suppose that we wish to study the possible galvanic corrosion between zinc and chromium, so we set up the following cell: Cr(s) | Cr²⁺(aq) || Zn²⁺(aq) | Zn(s).
    • What is the chemical reaction that takes place and what is the standard free energy change for that reaction?

    Equilibrium Constants

    • The cell potential can be used to calculate the equilibrium constant for an electrochemical reaction.
    • E = (RT/nF) ln K
    • n is the number of electrons transferred, R is the universal gas law constant, and F is Faraday's constant.
    • The relationship between the cell potential and the equilibrium constant can be re-written in terms of the common (base 10) log.
    • E = (2.303RT/nF) log K
    • The equation can be simplified for reaction carried out at standard temperature, 25°C (298 K).
    • E° = (0.0592/n) log K

    Example Problem 13.4

    • In a process called flash electroplating, a current of 2.50 × 10³ A passes through an electrolytic cell for 5.00 minutes. How many moles of electrons are driven through the cell?

    Example Problem 13.5

    • Suppose that a batch of parts is plated with copper in an electrolytic bath running at 0.15 V and 15.0 A for exactly 2 hours. What is the energy cost of this process if the electric utility charges the company $0.0500 per kWh?

    Calculations Using Masses of Substances in Electrolysis

    • A knowledge of current, how long the current flows, stoichiometry, and the number of electrons required to reduce a metal cation are used to answer the following questions.
    • How much material is plated given a specific current for an allotted time or electrical energy expenditure?
    • How long must a given current to pass through the cell to yield a desired mass of plated material?

    Example Problem 13.6

    • An electrolysis cell that deposits gold (from Au³⁺(aq)) operates for 15.0 minutes at a current of 2.30 A. What mass of gold is deposited?

    Example Problem 13.7

    • Suppose that you have a part that requires tin coating. You've calculated that you need to deposit 3.60 g of tin to achieve an adequate coating. If your electrolysis cell (using Sn²⁺) runs at 2.00 A, how long must you operate the cell to obtain the desired coating?

    Batteries in Engineering Design

    • Lithium-ion batteries have recently come under scrutiny because of a high-profile fire during the first commercial flight of the Boeing Dreamliner 787.
    • What factors led to the Dreamliner's problems?
      • The Dreamliner requires higher levels of electrical power than conventional aircraft due to replacing the traditional hydraulic system for controlling the flight with an all-electronic alternative.
      • Increased fuel efficiency was a major goal, so it was important to minimize weight. Lithium-ion batteries have high energy capacity and low weight.
    • The anode is a form of graphite into which lithium atoms have been incorporated, or “intercalated."
    • The cathode is cobalt oxide that also has lithium incorporated into it.
    • Two reasons energy density is high:
      • Li⁺/Li has one of the largest standard reduction potentials
      • Both lithium and carbon are relatively light
    • High temperatures cause lithium-ion batteries to degrade fairly quickly, so engineering designs that use them generally must account for this.

    Primary Cells

    • Single-use batteries that cannot be recharged are primary cells.
    • The most prevalent type of primary cell is the alkaline battery.
    • An alkaline battery has a zinc electrode at which oxidation occurs.
    • The cathode is derived from manganese(IV) oxide.
    • The chemistry of an alkaline dry cell battery. The net reaction is shown above.
    • The alkaline battery is termed a dry cell because the KOH electrolyte is in the form of a paste or gel.
    • Lithium batteries are small and long lasting. They are used for medical devices like pacemakers.
    • Lithium is the anode
    • Manganese(IV) oxide is the cathode, but in this case the MnO₂ reacts with lithium ions.
    • The lithium battery provides a stable current and electrical potential for long periods.
    • Zinc-air batteries are also primary cells.
    • Zinc is the anode.
    • Oxygen reacts at the cathode.

    Secondary Cells

    • Rechargeable batteries are secondary cells or secondary batteries.
    • Nickel-metal-hydride batteries are an example of secondary cells.
    • The anode reaction is MH(s) + OH⁻(aq) → M⁺ + H₂O(l) + e⁻.
    • The complex cathode reaction can be represented as NiO(OH)(s) + H₂O(l) + e⁻ → Ni(OH)₂(s) + OH⁻(aq)
    • Nickel is converted from NiO(OH) to Ni(OH)₂ at the cathode.
    • The cathode and anode materials are separated by an insulator throughout the battery.
    • Water reacts with a metal alloy to form an absorbed hydrogen atom and hydroxide ion at the anode.
    • The negative collector is in contact with the anode material.
    • Nickel-metal-hydride batteries have become popular as rechargeable cells.
    • The lead-acid storage battery found in cars is a secondary cell.
    • The anode for a lead-acid battery is lead metal.
    • The cathode for a lead-acid battery is lead oxide.
    • The lead-acid storage battery consists of Pb anodes alternating with PbO₂ cathodes, all immersed in sulfuric acid.

    Fuel Cells

    • A fuel cell is a voltaic cell in which the reactants can be supplied continuously and the products of the cell reaction are continuously removed.
    • Most common type is based on the reaction of hydrogen and oxygen to produce water.
    • Oxygen is reduced at the cathode.
    • Hydrogen is oxidized at the anode.

    Limitations of Batteries

    • Corrosion is a major cause for the loss of performance in batteries.
    • Protective plating of materials used in batteries is an attempt to limit the performance-diminishing effects of corrosion on batteries.

    Electrolysis

    • Electrolysis is the process of passing an electric current through an ionic solution or molten salt to produce a chemical reaction.
    • Electrolytic cells are divided into two categories based on the nature of the electrodes used.
      • Passive electrolysis: the electrodes are chemically inert materials that simply provide a path for electrons.
      • Active electrolysis: the electrodes are part of the electrolytic reaction.
    • Electrolysis changes the polarity of the electrodes in a system. For reduction, electrons are forced to the cathode. The cathode becomes the negative electrode. For oxidation, electrons are pulled from the anode. The anode becomes the positive electrode.
    • In electrolysis, an external source of current drives a redox reaction that would otherwise not be spontaneous. The flow of ions completes the circuit.

    Passive Electrolysis in Refining Aluminum

    • Electrolysis provides the means to overcome the nonspontaneous reaction to separate aluminum from its oxide.
    • The Hall-Heroult refining process uses carbon electrodes as inert sites for passive electrolysis.

    Active Electrolysis and Electroplating

    • The process of depositing a thin coat of metal on another metal by using electrolysis is electroplating.
    • In some cases, the thin coating is cosmetic, or to provide some vital functionality for the coated piece, such as corrosion resistance or desirable conductive properties.
    • Silver is plated onto electrical devices because silver is a good conductor and resistant to corrosion.
    • The object being electroplated is the cathode.
    • Anode Ag(s) + 2CN⁻(aq) → Ag(CN)₂⁻(aq) + e⁻
    • Cathode Ag(CN)₂⁻(aq) + e⁻ → Ag(s) + 2CN⁻(aq)
    • Silver is transferred from the anode to the cathode, coating the cathode in a thin layer of silver.
    • The zero cell potential is not critical since an external current drives electrolysis.
    • Barrel plating is often used to apply coatings to small parts.

    Electrolysis and Stoichiometry

    • For electroplating, it can be vitally important to use carefully controlled amounts of materials.
    • Controlling the flow of electrons (current) in an electroplating operation provides a method to accurately limit the amount of material deposited.
    • Electroplating is often used to prevent galvanic corrosion in an electrical apparatus in places where different metals come into contact with one another.

    Current and Charge

    • When current is measured in an electric circuit, the observation is the flow of charge for a period of time.
    • The unit of current, the ampere (A), is defined as one coulomb per second: 1 A = 1 C s⁻¹.
    • If a known current flows through a circuit for a known time, the charge can be easily calculated.
    • Charge = current × time, Q = I × t
    • Using Faraday's constant, F = 96,485 C mol⁻¹, and the calculated charge, the number of moles of electrons that pass through the circuit can be calculated.
    • If the number of electrons required to reduce each metal cation is known, the number of moles of material plated can be calculated.
    • Electricity use is often measured in terms of power. The SI unit for power is the watt (1 watt = 1 J s⁻¹).
    • Electrical utilities normally determine consumption in kilowatt-hours, kWh (1 kWh = 3.60 × 10⁶ J).

    Example Problem 13.4

    • In a process called flash electroplating, a current of 2.50 × 10³ A passes through an electrolytic cell for 5.00 minutes. How many moles of electrons are driven through the cell?

    Example Problem 13.5

    • Suppose that a batch of parts is plated with copper in an electrolytic bath running at 0.15 V and 15.0 A for exactly 2 hours. What is the energy cost of this process if the electric utility charges the company $0.0500 per kWh?

    Example Problem 13.6

    • An electrolysis cell that deposits gold (from Au³⁺(aq)) operates for 15.0 minutes at a current of 2.30 A. What mass of gold is deposited?

    Example Problem 13.7

    • Suppose that you have a part that requires tin coating. You've calculated that you need to deposit 3.60 g of tin to achieve an adequate coating. If your electrolysis cell (using Sn²⁺) runs at 2.00 A, how long must you operate the cell to obtain the desired coating?

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    Test your knowledge on oxidation-reduction reactions with this quiz. Explore concepts related to galvanic cells, reducing agents, and the effects of copper on silver nitrate. Understand the fundamental principles that govern these essential chemical processes.

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