Chapter19

Calcium is plated onto an electrode through the reduction reaction Ca2+ (aq) + 2e- → Ca (s). Which equation would be used to calculate the mass of calcium that is deposited in 30.0 seconds at using a current of 2.0 A?

(2.0A)(30.0s)(40.1gmol)/ (96,485Cmol)(2)

A standard electrochemical cell is constructed from an anode that has a standard reduction potential of -2.0 V and a cathode that has a standard reduction potential of +0.5 V. Which of the following is the correct expression to calculate the standard cell potential?

+0.5 + 2.0

Given the standard potential for the half-reaction Ag+ (aq) + e- → Ag (s); Eo = +0.80 V, determine the standard reduction potential for the half-reaction 2Ag+ (aq) + 2e- → 2Ag (s).

+0.80 V

Co3+ (aq) + Cu (s) → Co2+ (aq) + Cu+ (aq) Calculate the standard cell potential for the reaction above, given the following information: Co3+ (aq) + e- → Co2+ (aq); Eo = 1.842 V Cu+ (aq) + e- → Cu (s); Eo = 0.521 V

+1.321 V

Place the following steps for balancing a redox reaction that occurs in acidic solution in the correct order. Start with the first step at the top of the list.

- separate the unbalanced reaction into half reactions - balance each half-reaction with regard to atoms. add H2O to each half-reaction as needed to balance oxygen, and add H+ as needed to balance hydrogen - balance the charges in each half-reactions by adding electrons where appropriate - multiply the balanced half-reactions by the appropriate factors to set the number of electrons on each side to be equal to each other - add the two half-reactions together and cancel any identical terms that appear on both sides

Given the standard potential for the half-reaction Ca2+ (aq) + 2e- → Ca (s) is -2.87 V, what is the standard potential for the half-reaction 2Ca2+ (aq) + 4e- → 2 Ca (s)?

-2.87 V

Ag(s) + Li+(aq) → Ag+(aq) + Li(s) Calculate the standard cell potential for the above reaction given the following information: Li+ (aq) + e- → Li (s); Eo = -3.045 V Ag+ (aq) + e- → Ag (s); Eo = 0.799 V

-3.844 V

Match the oxidation number of chlorine with the appropriate chemical compound

-NaClO4 +7 -HCl -1 -KClO +1 -RbClO3 +5

During operation of a galvanic cell, electrons flow from the anode to the cathode, resulting in product formation and a decrease in reactant concentrations. At equilibrium there is no net transfer of electrons so E = _____.

0

A concentration cell is constructed with an overall redox equation of Zn2+ (0.50 M) → Zn2+ (0.15 M). What is the cell potential for this concentration cell at 25∘C?

0.015 V

Identify the number of electrons required to balance the following half-reaction. Also indicate whether these electrons must appear as reactants or products. 2H+ + NO3- → NO2 + H2O

1 e-, reactant

Prior to balancing oxygen and hydrogen atoms, identify the missing coefficients in the half-reaction _____ NO2- → _____ NH4+.

1, 1

When the half-reactions below are balanced to each other, the first reaction should be multiplied by _____, and the second reaction should be multiplied by _____. Equation 1: 2H2O → O2 + 4H+ + 4e- Equation 2: Ni2+ + 2e- → Ni

1, 2

When hydrogen atoms are balanced in the following (unbalanced) half-reaction, identify the amount of the substance that must be introduced, and where it will appear in the equation. Assume the reaction occurs in acidic medium. 2ClO3- → Cl2 + 6H2O

12H+ must be added as a reactant.

Given the following (unbalanced) half-reaction, identify the missing coefficient when atoms other than O are balanced. Mn2O3 → _____ MnO2

2

Identify the number of water molecules needed to balance the following half-reaction. Also indicate whether the water will appear as a reactant or a product. MnO4- → MnO2

2 H2O, product

When calcium ions (Ca2+) are electrolytically reduced to calcium metal, what is the relationship between the moles of electrons transferred and the moles of Ca (s) produced?

2 mol of e- will be transferred for every 1 mol Ca (s) produced.

Which of the following are true when the reactions below are added together? Make sure you eliminate species that appear on both sides of the equation. Reaction 1: 2BiO+ + 4H+ + 6e- → 2Bi + 2H2O Reaction 2: 6H2O → 3H2O2 + 6H+ + 6e-

2 moles of H+ appear as a product. 4 moles of H2O appear as a reactant.

The reaction shown below occurs in a basic solution. Select all the options that correctly describe the balanced equation obtained after all resulting species are combined and/or canceled correctly. MnO2 + 4H+ + Zn → Mn2+ + 2H2O + Zn2+

2 moles of H2O appear among the reactants. 4 moles of OH- appear among the products.

When hydrogen and oxygen atoms are balanced in the following half-reaction, which of the following statements are correct? Select all that apply. TiO2 (s) → Ti (s)

2 moles of H2O appear as a product. 4 moles of H+ appear as a reactant.

When the half-reactions below are balanced to each other, the first reaction should be multiplied by _____, and the second reaction should be multiplied by _____. Reaction 1: Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O Reaction 2: S + 3H2O → H2SO3 + 4H+ + 4e-

2, 3

Which of the following electrochemical reactions are spontaneous under standard conditions? Select all that apply.

2Cr (s) + 3Sn4+ (aq) → 2Cr3+ (aq) + 3Sn2+ (aq); Ecello = 0.89 V 2Co (s) + 3Cl2 (g) → 2CoCl3 (aq); Ecello = 1.6 V

Which of the following half-reactions could occur at the cathode of a galvanic cell? Select all that apply.

2H+ (aq) + 2e- → H2 (g) Ni2+ (aq) + 2e- → Ni (s)

An aqueous solution of CuBr2 is placed in an electrolytic cell. Which of the following reactions may occur at the cathode? Select all that apply.

2H2O (l) + 2e- → H2 (g) + 2OH- (aq) Cu2+(aq) + 2e- → Cu (s)

What is the spontaneous reaction that occurs when the following half-cells are combined? Zn2+ (aq) + 2e- → Zn (s); Eo = -0.76 V Na+ (aq) + e- → Na (s); Eo = -2.71 V

2Na (s) + Zn2+ (aq) → 2Na+ (aq) + Zn (s)

A metal object is to be plated with Cr metal by electrolysis of aqueous Cr2(SO4)3. Determine the number of electrons transferred and the total charge per mole of Cr (s) produced.

3 mol e- per mole of Cr (s) The total charge is 3 x 96,500 = 2.90 x 105 C.

When the two half-reactions below are added together (ensuring that the electrons cancel), which of the following is the net reaction? Reaction 1: Cu2+ + 2e- → Cu Reaction 2: Fe → Fe3+ + 3e-

3Cu2+ + 2Fe → 3Cu + 2Fe3+

A concentration cell is constructed based on the equation Ag+ (1.0 M) + Ag (s) → Ag (s) + Ag+ (x M). When a silver electrode is immersed into this cell at 25.0oC and it is tested against a 1.0 M AgNO3/Ag electrode, a 0.250-V cell potential develops. Calculate the concentration of the electrolyte in the anode compartment. E = Eocell - 0.0592n0.0592n log Q

6.03 x 10-5 M

Which of the following are correct regarding the movement of electrons and ions in a galvanic cell?

A salt bridge allows ions to flow from one half-cell to another. Electrons flow from the anode to the cathode, and cations move toward the cathode and anions move toward the anode. Without a salt bridge, positive and negative charge would build up in the half-cells and electrons would cease to flow.

What is the spontaneous reaction that occurs when the two half-cells below are combined? Fe3+ (aq) + e- → Fe2+ (aq); Eo = 0.77 V Ag+ (aq) + e- → Ag (s); Eo = 0.80 V

Ag+ (aq) + Fe2+ (aq) → Ag (s) + Fe3+ (aq)

Which of the following correctly describe the electrolysis of water? Select all that apply.

An electrolyte such as H2SO4 is required for this reaction. Hydrogen gas is generated at the cathode.

The two electrodes of an electrolytic cell are placed in a sample of molten zinc iodide. After a time, reddish-brown I2 (s) begins to form at one electrode while gray Zn (s) deposits on the other. Which of the following options correctly describe the process occurring? Select all that apply.

At the cathode, Zn2+ ions are reduced to form Zn (s). The half-reaction occurring at the anode is represented by 2I- (l) → I2 (s) + 2e-.

Which of the following options correctly describe the processes that occur during electrolysis of an aqueous solution of an electrolyte? Select all that apply.

Both H2O and any negative ions present might be oxidized. The species with the most positive reduction potential will likely be reduced at the cathode. Competing reduction and oxidation reactions are possible.

When molten NaCl undergoes electrolysis, which of the following occurs?

Chlorine ions are oxidized according to the following reaction: 2 Cl-(l) → Cl2(g) + 2e-.

1.00 moles of Zn and 0.500 moles of Zn2+ ions in 1.00 L of solution are used to form one half-reaction cell, while 2.00 moles of Cu and 3.00 moles of Cu+ in 1.00 L of solution are used to form a second half-reaction cell. The equation for the overall cell reaction is given by Zn (s) + 2Cu+ (aq) → Zn2+ (aq) + 2Cu (s). Which of the following values are correct based on the information provided if the temperature is 298 K and Eo = 0.91 V? Select all that apply.

E = 0.95 V Q = 0.0556

Which of the following are valid forms of the Nernst equation, which relates cell potential under nonstandard conditions to the standard cell potential? Select all that apply.

E = Eo - 0.0592V/n log Q (at 298 K) E = Eo - RT/nF ln Q

The Nernst equation relates ______.

E to Eο

Which of the following options describe the additional step(s) required to balance a redox reaction that takes place in a basic solution (as opposed to an acidic solution)? Select all that apply.

Each OH- ion added will combine with one H+ that is on the same side of the equation to form H2O. OH- must be added to each side of the equation in order to react with H+.

In general, when the concentration of the reactants in an electrochemical reaction is large, and the concentration of products is small, which of the following will be true regarding the relationship between Ecell and Ecello?

Ecell > Ecello

True or false: There are no electrons transferred in a redox reaction if there is no wire connecting the two half reactions.

False Reason: Electrons can spontaneously flow between the oxidized and reduced species without a wire. However, to harness the electron flow, a Galvanic cell is setup whereby the two half reactions are separated and connected via wire and salt bridge.

Which of the following are correct regarding the Faraday constant?

Faraday units can be expressed as J/V⋅mol e-. One Faraday is equivalent to 96,500 Coulombs per mole of electrons. The total charge of a cell is equal to the number of moles of electrons times the Faraday constant.

Match each type of electrochemical cell with the appropriate description.

For a voltaic cell - DeltaG < 0 For an electrolytic cell - DeltaG > 0 Work is done on the system in a(n) - Electrolytic cell The system does not work on the surroundings in a(n) - Voltaic cell

The standard hydrogen electrode (SHE) is assembled by immersing a piece of platinum in a 1.00 M acid (H+) solution in the presence of 1.00 atm H2 gas. Identify the role played by each component of this cell.

H+(aq) - Reactant in reduction reaction H2(g) - Product in reduction reactant Pt(s) - Electrode

Na+ + e- → Na; Eo = -2.7 V Cl2 + 2e- → 2 Cl-; Eo = 1.4 V 2H2O + 2e- → H2 + 2OH-; Eo = -0.4 V O2 + 4H+ + 4e- → 2H2O; Eo = -0.82 V An aqueous NaCl solution is electrolyzed. What are the products at the cathode and anode?

H2 and OH- form at the cathode; Cl2 forms at the anode.

To which of the following half-reactions must 2 electrons appear as products in order to balance the equation?

H2O + PbO → PbO2 + 2H+ H2 + 2OH- → 2H2O

For the chemical reaction shown below, which of the following (unbalanced) reactions should be used as the starting point for the reduction half-reaction? 2Na + 2H2O → 2NaOH + H2

H2O → H2

When a redox reaction that takes place in an acidic solution involves an oxygen imbalance, oxygen should be balanced by adding _____ as needed, while hydrogen should be balanced by adding _____.

H2O, H+

Which of the following options correctly describe the standard hydrogen electrode? Select all that apply.

Hydrogen gas at a pressure of 1 atm is bubbled through the electrolyte solution. The electrode is immersed in a 1-M solution of aqueous HCl.

Match each symbol in the cell notation shown below with its correct meaning. Pb (s) Ι Pb+ (1 M) ΙΙ Co3+ (1 M) Ι Co (s)

I - Boundary between two phases in the same half-cell II - The salt bridge Zn(s) - Anode Cu(s) - Cathode

If ΔGo for a reaction is equal to 0, what must be true regarding the equilibrium constant?

K = 1

In which of the following (unbalanced) half-reactions will 1 mole of water appear as a reactant when oxygen atoms are balanced? Select all that apply.

N2O5 → 2NO3 Na → NaOH

Na+ + e- → Na; Eo = -2.7 V Cl2 + 2 e- → 2 Cl-; Eo = 1.4 V Consider the reactions occurring in an electrolytic cell at two inactive electrodes immersed in anhydrous molten sodium chloride. Which products form at the cathode and anode?

Na forms at the cathode; Cl2 forms at the anode.

The reaction below is spontaneous in the forward direction. Which of the statements below provides the best reason for this observation? Ni (s) + 2Ag+ (aq) → Ni2+ (aq) + 2Ag (s)

Ni (s) gives its electrons away more freely than Ag (s).

Given the two half-reactions below, which reaction will be the reduction reaction in the spontaneous reaction that would occur between them? Cr3+ + 3e- → Cr; Eo = -0.74 V Ni2+ + 2e- → Ni; Eo = -0.28 V

Ni2+ + 2e- → Ni

Which of the following must be balanced in order to balance a redox reaction? Select all that apply.

Number of atoms of each type Overall charge

Which of the following options correctly describes how to use a table of standard reduction potentials to write the equation for the half-reaction that occurs at the anode?

Reverse the appropriate reduction half-reaction.

Which of the following statements correctly describes standard electrode potentials?

Standard reduction potentials are measured for solutes at 1 M and gases at 1 atm.

Which of the following options correctly describe the shorthand notation used to represent an electrochemical cell? Select all that apply.

The anode is written first, on the left side of the cell notation. A single vertical line in cell notation represents a phase boundary.

Which of the following statements correctly describe tabulated standard electrode potentials?

The best oxidizing agents will be reactants in half-reactions with the most positive cell potentials.

Which of the following best explains why the following chemical reaction is not balanced? Cu2+ (aq) + Fe (s) → Cu (s) + Fe3+ (aq)

The charge is not balanced

Which of the following are correct regarding the flow of electrons within a galvanic cell?

The flow of electrons in a galvanic cell can be likened to the flow of water down a waterfall. The stronger reducing agent in a galvanic cell supplies electrons spontaneously to create an electrical current. Electrons flow spontaneously in a galvanic cell.

Using a current of 4.75 A, a sculpture is copper plated with 1.50 g of Cu by electrolysis of a CuSO4 solution. Which of the following options correctly reflect the processes required to calculate the time required for this process? Select all that apply.

The half-reaction is Cu2+(aq) + 2e- → Cu(s). The process will take 16.0 minutes. There are 4.72 × 10-2 moles of electrons transferred.

Which of the following are correct regarding the standard hydrogen electrode?

The hydrogen electrode is used as a reference for the measurement of other electrode potentials. The potential value of the hydrogen electrode has been arbitrarily set to zero volts. The potentials of individual half-cells cannot be measured without being coupled to another half-reaction.

When zinc metal is immersed in a 1.0-M solution of copper (II) chloride at 25oC, no electrochemical work may be extracted, even though a spontaneous reaction occurs. What is wrong this this cell design?

The oxidation and reduction reactions must be physically separated.

Which of the following options correctly identify the abbreviation for cell potential and its units? Select all that apply.

The symbol for cell potential is Ecell. The unit of cell potential is the volt, symbol V.

Which of the following options correctly describe the units used to express electrical potential, charge, and electrical energy? Select all that apply.

The volt is the unit for electrical potential. Electrical energy can be measured in joules.

True or false: The overvoltage is the difference between the calculated voltage for a cell and the actual voltage required for electrolysis.

True

Based on the following reaction, identify ALL the species that should be included in the oxidation half-reaction equation. Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s)

Zn2+ (aq) Zn (s)

If we were to solve for the cell potential of the following reaction, which two reactions would we first need to find in a standard reduction table? 2Ag+ (aq) + Zn (s) → 2Ag (s) + Zn2+ (aq)

Zn2+ (aq) + 2e- → Zn (s) Ag+ (aq) + e- → Ag (s)

In a galvanic cell, electrons are generated due to the oxidation reaction at the _____, and flow through the external circuit toward the _____.

anode, cathode

In a galvanic cell, the electrode at which the oxidation reaction occurs is called the _____, while the electrode at which the reduction reaction occurs is called the _____.

anode, cathode

If one were to construct an electrochemical cell consisting of two Zn2+/Zn electrodes at two different concentrations, the more concentrated cell will be the _____.

cathode

The standard cell potential may be solved using the equation Eocell = Eo _____- Eo _____.

cathode, anode

An electrochemical cell that is constructed using the same electrode in both half-cells with different concentrations of electrolyte in each is called a(n) ______cell.

concentration

The SI unit of current is the ampere, which is defined as the flow of charge in units of _____ over a period of time measured in _____.

coulombs, seconds

Which of the following options currently express the relationship between the charge passing through an electrochemical cell and the current flowing? Select all that apply.

current (A) = charge/time C = A x s

The process in which electrical energy is used to drive a nonspontaneous electrochemical reaction is called_____.

electrolysis

The Faraday constant allows one to convert between moles of _____ and the equivalent amount of charge in units of ______.

electron, coulomb

The maximum amount of useful work a chemical system can supply is related to the value of the _____ for the reaction.

free-energy change

The experimental apparatus for generating electricity through the use of a spontaneous chemical reaction is called a ______ cell.

galvanic

A(n) _____ cell exploits a spontaneous redox reaction to generate electrical energy, whereas a(n) _____ cell requires a continuous input of electrical energy.

galvanic; electrolytic

By definition, if one coulomb of charge passes between two electrodes that differ in potential by one ______ volt, one of energy is released. This relationship is correctly expressed as V = ______ /_____. (Fill in units only, without values.)

joule, J/C

Oxidation involves the _____ of electrons, while reduction involves the _____ of electrons.

loss; gain

If due to a change in reaction conditions the standard cell potential (Eo) of an electrochemical reaction becomes more negative, the standard free-energy change (ΔGo) will become _____, and the equilibrium constant (Keq) will become _____.

more positive, smaller

Which of the following is required to solve for the nonstandard cell potential using the Nernst equation? Select all that apply.

n (the number of electrons in the balanced reaction) E°, the standard cell potential Q, the reaction quotient

The Nernst equation is used to calculate the cell potential under _________ conditions. The cell potential is found to differ from the standard cell potential by a factor proportional to the natural log of the reaction ______ (Q).

nonstandard, quotient

The difference between the calculated voltage (based on standard potentials) and the actual voltage required to cause electrolysis is called ______.

overvoltage

When predicting the spontaneous reaction between two different half-cells, the reaction with the most negative cell potential will be the _____ reaction, while the reaction with the most positive cell potential will be the _____ reaction.

oxidation; reduction

If a substance causes another substance to be oxidized, that substance is a(n) ________ agent. Likewise, the substance that is oxidized in an electrochemical reaction is always the _______ agent.

oxidizing, reducing

As listed in a table of standard electrode potentials, the reactants in the half-reactions are potential _____ agents, while the products of the half-reactions are potential _____ agents.

oxidizing; reducing

The measure of energy used in electrochemistry is the cell (Ecell), _________ which is the difference in electrical potential between two electrodes. A common term for this difference in electrical potential is _______ force or emf.

potential, electromotive

The standard ______ potential for a half-reaction is the voltage associated with the reduction reaction at an electrode when all solutes are at a concentration of 1 M and gases are at _____ atm of pressure.

reduction, 1

If ΔGo < 0, the reaction is _____ as written; if K < 1, the reaction is _____ as written.

spontaneous, nonspontaneous

The cell potential for the standard hydrogen electrode (SHE) is by definition equal to ______ volts. If this half-cell is used as the anode and all of the substances in the cathode are under standard conditions, then the potential of the cell is equal to the standard ______ potential of the cathode.

zero, reduction

Which of the following options correctly expresses the relationship between free-energy change and cell potential?

ΔG = -nFEcell

How is the change in free energy (ΔG) of a chemical system related to work?

ΔG represents the maximum useful work that a reaction can supply.