CHEM 112 SB ELECTROCHEMISTRY ASSIGNMENT

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?

(2.0 A)(30.0 s)(40.1g Camol Ca)(96,500Cmol e−)(2mol e-mol Ca)

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

KClO

+1

Na

+1

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 Reason: Eocell = Eocathode - Eoanode. Since Co3+ is reduced it is the cathode, and Eocell = 1.842 - 0.521 = 1.321 V. Using this equation for cell potential one does NOT reverse the sign of the standard potential for the oxidation half-reaction.

Ca

+2

RbClO3

+5

NaClO4

+7

F

-1

HCl

-1

O

-2 (or -1)

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 Reason: Changing the coefficients of a half-reaction does not change the Eohalf-cell.

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 Reason: Since Li+ is reduced, it is the cathode. Eocell = Eocathode - Eoanode. The standard reduction potentials are used in this equation without changing any signs.

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 Reason: There are 2 electrons for this reaction. Therefore, n = 2 as follows: E = 0 - 0.0592V/2 log 0.15/0.50 = 0.015 V.

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 catode are under standard condtions, then the potential of the cell is equal to the standard _____ potential of the cathode.

0; reduction

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) produ

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

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

2Co (s) + 3Cl2 (g) → 2CoCl3 (aq); Ecello = 1.6 V 2Cr (s) + 3Sn4+ (aq) → 2Cr3+ (aq) + 3Sn2+ (aq); Ecello = 0.89 V Reason: A negative cell potential indicates a nonspontaneous reaction.

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) Reason: Only reduction occurs at the cathode, meaning that electrons will be gained (shown on the reactants' side).

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) Reason: Na (s) + Zn2+ (aq) → Na+ (aq) + Zn (s) is not a balanced reaction. Notice that the total charge on the left is +2, while it is +1 on the right.

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 - 0.0592/n log Q

6.03 x 10-5 M Reason: 0.250 = 0 - 0.0592/ log x/1.00 = -0.0592 log x log x = -(0.250/0.0592) = -4.22 x = 10^-4.22 = 6.03 x 10-5

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

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

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) Reason: In order to be spontaneous, the half reactions must be arranged so that the net cell potential is positive. Reason: One of the two reactions must be reversed since there must be an oxidation process.

Which of the following are examples of cathodic protection? (Select all that apply.)

An aluminum anode is attached to a steel beam to keep it from corroding. A coating of zinc is applied to an iron pipeline to keep it from corroding. A magnesium metal bar is connected to a steel ship hull to keep it from rusting.

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. Reason: Since the two gases form at two different electrodes, it is possible separate them.

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

Anode; cathode

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.

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. Reason: Since standard half-reactions are written as reduction half reactions, the reactants are potential oxidizing agents while the products are potential reducing agents.

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-. Reason: Zn2+ ions are reduced at the cathode, which is the negative electrode in an electrolytic cell. Reason: I- ions are oxidized to I2 (s) in this reaction.

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.

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

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

Cathode; anode

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-.

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

Competing reduction and oxidation reactions are possible. 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.

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) _____

Concentration

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

anode

Cu (s) → Cu+ (aq) + e-

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 - 0.0592 V/n log Q E = Eo - RT/nF ln Q

Which of the following is not a variation of the Nernst equation?

E = E° + RT/nF ln Q

Q > K

Ecell < 0

Q > 1

Ecell < Ecello

Q = K

Ecell = 0

Q = 1

Ecell = Ecello

Q < K

Ecell > 0

Q < 1

Ecell > Ecello

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 Reason: Correct, the reaction will be more spontaneous (with a more positive cell potential). Ecell > Ecello Reason: Ecell < Ecello would imply that the reaction would be less spontaneous when compared to standard conditions. Reactions tend to be more spontaneous as reactant concentrations increase.

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

Electrical energy can be measured in joules. The volt is the unit for electrical potential. Reason: 1 joule = 1 V x 1 C Reason: The unit for electrical charge has the symbol C. Reason: The coulomb is the unit for electrical charge. The unit for emf or voltage is the volt.

Pt (s)

Electrode

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 _____

Electrons; coulombs (C)

cathode

Fe3+ (aq) + e- → Fe2+ (aq)

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. Reason: The substance with the least negative reduction potential is reduced (H2O to H2), while the substance with the least positive oxidation potential is oxidized (Cl- to Cl2 at -1.4 V).

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. Reason: The standard reduction potential for the hydrogen cell is defined as 0.00 V.

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

Ecell = Ecello - RT/nF ln Q Based on the Nernst equation (given above), how does the magnitude of Q affect the cell potential?

Look below.

Match each electrode in an electrolytic cell with the correct description.

Look below.

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)

Look below.

Match each type of electrochemical cell with the appropriate description.

Look below.

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

Loss; gain

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). Reason: Even though Ni (s) gives its electrons away more freely than Ag+ (aq), it does not explain the direction of spontaneity for this reaction. We must compare the relative energies of the reactants to the products.

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 Reason: Cr3+ + 3e- → Cr has a more negative cell potential. It will not be the spontaneous reduction reaction. Reason: Cr → Cr3+ + 3e- is an oxidation reaction (in fact, it is the more spontaneous oxidation reaction of the two choices). Reason: Ni → Ni2+ + 2e- is an oxidation reaction.

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 _____.

Nonstandard; quotient

Which of the following are correct regarding the Faraday constant?

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

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

Overall charge Number of atoms of each type

H2 (g)

Product in reduction half-cell

Eocell > 0

Products are favored at equilibrium.

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.

Q = 0.0556 E = 0.95 V

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

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

H+ (aq)

Reactant in reduction half-cell

Eocell < 0

Reactants are favored at equilibrium.

Ecell = 0

Reaction is at equilibrium.

Ecell < 0

Reaction is nonspontaneous.

Ecell > 0

Reaction is spontaneous.

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?

Reason: Eocell = Eocathode - Eoanode = 0.5 - (-2.0) = 0.5 + 2.0

Reason: The table of standard reduction potentials lists all half-reactions as reduction half-reactions. To write the equation for the oxidation half-reaction, the appropriate reduction half-reaction must be reversed.

Reverse the appropriate reduction half-reaction.

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.

Match each element with its most common oxidation number (assuming it is in a polar covalent or ionic bond).

See below

Match the oxidation number of chlorine with the appropriate chemical compound.

See below

Identify the half-reactions that occur at the cathode and the anode in the overall redox reaction Fe3+ (aq) + Cu (s) → Cu+ (aq) + Fe2+ (aq)

See below.

Match each cell potential with its implication for reaction spontaneity and the extent of reaction at equilibrium.

See below.

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.

See below.

Match the relative values of the reaction quotient and equilibrium constant to the associated value of the nonstandard cell potential.

See/Look below.

Which of the following options correctly describe corrosion? Select all that apply.

Some metals oxidize to form a protective coating, which prevents further corrosion. During corrosion the metal surface supplies both the cathode and the anode. During corrosion, a metal is oxidized.

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. Reason: Standard reduction potentials are measured relative to the potential of the standard hydrogen electrode.

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. Reason: Every reaction is reversible, given the proper driving force. Even F- may be oxidized to F2, given enough energy. Reason: Reducing agents are always the products of reduction half-reactions (since they must be oxidized).

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.

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

The electrode is immersed in a 1-M solution of aqueous HCl. Hydrogen gas at a pressure of 1 atm is bubbled through the electrolyte solution. Reason: The standard reduction potential for the hydrogen cell is defined as 0.00 V.

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

The potentials of individual half-cells cannot be measured without being coupled to another half-reaction. 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. Reason: The potential value of the hydrogen electrode half-cell is set to zero, and when paired with another half-cell the standard reduction potential can be measured.

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

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

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.

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

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

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

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.

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

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

True Reason: The calculated voltage for an electrolytic cell sometimes deviates from the actual voltage required. This difference is known as the overvoltage.

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

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

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) Reason: Half-cell potentials are tabulated as reduction reactions, so we must look for the reduction of Ag+ and reverse the reaction to obtain the oxidation half-reaction.

Pb (s)

anode

Oxidation occurs at the

anode.

Co (s)

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 Reason: A concentrated solution will tend to become less concentrated. In this case, concentrated Zn2+ becomes reduced.

Reduction occurs at the

cathode.

The deterioration of metals by an electrochemical process is called _____. The metal is oxidized during this process.

corrosion

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

The system does work on the surroundings in a(n)

electrolytic cell.

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

A sacrificial anode can be used to protect a metal like iron from corrosion. In order for this to work, the anode must be _____ than the metal that it is protecting.

more active

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

Ι

phase boundary

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 (or voltage); electromotve

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

ΙΙ

salt bridge

For an electrolytic cell

voltaic cell.

For a voltaic cell

ΔG < 0.

Work is done on the system in a(n)

ΔG > 0.