HW11 - Electrochemical Potential, Free Energy, and Application

Question 11.0 pts

What is the E°cell for

Zn(s) | Zn2+(aq) || Ce4+(aq) | Ce3+(aq)

Zn2+ + 2e- \longrightarrow Zn            E° = -0.76

Ce4+ + e- \longrightarrow Ce3+          E° = +1.61

  1. 2.37 V
  2. 1.61 V
  3. -2.37 V
  4. 0.85 V

Question 21.0 pts

Standard reduction potentials are established by comparison to the potential of which half-reaction?
  1. 2H+ + 2e- \longrightarrow H2
  2. F2 + 2e- \longrightarrow 2F-
  3. Li+ + e- \longrightarrow Li
  4. 2H2O + 2e- \longrightarrow H2 + 2OH-

Question 31.0 pts

What is the standard cell potential of the strongest battery that could be made using these half-reactions?

Br2 + 2e- \longrightarrow 2Br-        E° = +1.07

Fe3+ + 3e- \longrightarrow Fe       E° = -0.04

Co3+ + e- \longrightarrow Co2+     E° = +1.80

Zn2+ + 2e- \longrightarrow Zn       E° = -0.76

  1. 2.56
  2. -2.56
  3. 1.11
  4. 1.84

Question 41.0 pts

What would be the E° of an electrolytic cell made from the half-reactions below?

AgCl(s) + e- \longrightarrow Ag(s) + Cl-(aq)         E° = +0.22 V

Al3+(aq) + 3e- \longrightarrow Al(s)                      E° = -1.66 V

  1. -1.88
  2. 1.88
  3. 1.44
  4. -1.44

Question 51.0 pts

Sodium is produced by the electrolysis of molten sodium chloride. What are the products at the anode and cathode, respectively?
  1. Cl2(g) and Na(l)
  2. Cl2(g) and Na2O(l)
  3. Na(l) and O2(g)
  4. O2(g) and Na(l)

Question 61.0 pts

The electrolysis of an aqueous sodium chloride solution using inert electrodes produces gaseous chlorine at one electrode. At the other electrode gaseous hydrogen is produced and the solution becomes basic around the electrode. What is the equation for the cathode half-reaction in the electrolytic cell?
  1. 2H2O + 2e- \longrightarrow H2 + 2OH-
  2. Cl2 + 2e- \longrightarrow 2Cl-
  3. H2 + 2OH- \longrightarrow 2H2O + 2e-
  4. 2Cl- \longrightarrow Cl2 + 2e-

Question 71.0 pts

The galvanic cell below uses the standard half-cells Mg2+ | Mg and Zn2+ | Zn, and a salt bridge containing KCl(aq).

GenericBatt.png

Identify A and write the half-reaction that occurs in that compartment.

  1. Mg(s); Mg(s) \longrightarrow Mg2+(aq) + 2e-
  2. Zn(s); Zn2+(aq) + 2e- \longrightarrow Zn(s)
  3. Mg(s); Mg2+(aq) + 2e- \longrightarrow Mg(s)
  4. Zn(s); Zn(s) \longrightarrow Zn2+(aq) + 2e-

Question 81.0 pts

Refer to the diagram in question 7. What happens to the size of the electrode A during the operation of the cell?
  1. it increases
  2. it decreases
  3. it doesn't change
  4. There is no way to tell.

Question 91.0 pts

Refer to the diagram in question 7. What should the voltmeter read?
  1. +4.30 V
  2. +3.40 V
  3. +1.60 V
  4. +2.50 V

Question 101.0 pts

How many moles of Cl2(g) are produced by the electrolysis of concentrated sodium chloride if 2.00 A are passed through the solution for 4.00 hours? The equation for this process (the "chloralkali" process) is given below.

2NaCl(aq) + 2H2O(l) \longrightarrow 2NaOH(aq) + H2(g) + Cl2(g)

  1. 0.00248 mol
  2. 0.149 mol
  3. 0.298 mol
  4. 0.0745 mol

Question 111.0 pts

A steel surface has been electroplated with 5.10g of vanadium (V, molar mass = 51 g/mol). If 2.90x104 C of charge were used, what was the original oxidation number of V?
  1. +3
  2. +4
  3. +2
  4. +1

Question 121.0 pts

How long will it take to deposit 0.00235 moles of gold by the electrolysis of KAuCl4(aq) using a current of 0.214 amperes?
  1. 106 min
  2. 70.7 min
  3. 53.0 min
  4. 26.5 min

Question 131.0 pts

Consider 3 electrolysis experiments:

1. One Faraday of electricity is passed through a solution of AgNO3.

2. Two Faradays of electricity are passed through a solution of Zn(NO3)2.

3. Three Faradays of electricity are passed through a solution of Bi(NO3)3.

Which of the following statements is true?

  1. Equal numbers of moles of all three metals are produced.
  2. The reaction producing the smallest mass of metal is that of the silver solution.
  3. Twice as many moles of metallic zinc are produced than metallic silver.
  4. Equal masses of all three metals are produced.

Question 141.0 pts

What is \Delta G^\circ for the half-reaction below?

ClO3- + 6H+(aq) \longrightarrow 0.5Cl2(g) + 3H2O(l)        E° = +1.47

  1. 194 kJ/mol
  2. 194,000 kJ/mol
  3. -709 kJ/mol
  4. -709,000 kJ/mol

Question 151.0 pts

For the reduction of Cu2+ by Zn, \DeltaG° = -212 kJ/mol and E° = +1.10 V. If the coefficients in the chemical equation for this reaction are multiplied by 2, \DeltaG° = -424 kJ/mol. Does this mean E° for the cell would be +2.20V?
  1. It is impossible to know without testing it empirically.
  2. No.
  3. Yes.
  4. Not enough information is given.

Question 161.0 pts

Consider the cell:

Zn(s) | Zn2+(aq) || Fe2+(aq) | Fe(s)

If run at standard conditions, calculate the value of \Delta G^\circ_{rxn} for the reaction that occurs when current is drawn from this cell.

  1. -62 kJ/mol
  2. +62 kJ/mol
  3. -31 kJ/mol
  4. -230 kJ/mol

Question 171.0 pts

Calculate the cell potential for a cell based on the reaction below:

Cu(s) + 2Ag+(aq) \longrightarrow Cu2+(aq) + 2Ag(s)

when the concentrations are as follows:

[Ag+] = 0.7 M

[Cu2+] = 0.9 M

(The temperature is 25°C and E° = 0.4624 V.)

  1. 0.470 V
  2. 0.455 V
  3. 0.447 V
  4. 0.459 V

Question 181.0 pts

Consider the cell:

Pb(s) | PbSO4(s) | SO42-(aq, 0.60 M) || H+(aq, 0.70 M) | H2(g, 192.5 kPa) | Pt

If E° for the cell is 0.36 V at 25°C, write the Nernst equation for the cell at this temperature.

  1. E\:=\:0.36-0.01285\cdot\ln\frac{1.90}{\left(0.70\right)^2\left(0.60\right)}
  2. E\:=\:0.36-0.01285\cdot\ln\frac{192.5}{\left(0.70\right)^2\left(0.60\right)}
  3. E\:=\:0.36-0.02569\cdot\ln\frac{192.5}{\left(0.70\right)^2\left(0.60\right)}
  4. E\:=\:0.36-0.01285\cdot\ln\frac{1.90}{\left(0.70\right)\left(0.60\right)}

Question 191.0 pts

A concentration cell consists of the same redox couples at the anode and the cathode and different concentrations of the ions in the respective compartments. Find the unknown concentration for the following cell:

Pb(s) | Pb2+(aq, ?) || Pb2+(aq, 0.1 M) | Pb(s)      E = 0.065 V

  1. 7.97 x 10-3 M
  2. 1.26 M
  3. 6.35 x 10-4 M
  4. 15.8 M

Question 201.0 pts

What is the ratio of [Co2+] / [Ni2+] when a battery built from the two half-reactions below reaches equilibrium?

Ni2+ \longrightarrow Ni        E° = -0.25 V

Co2+ \longrightarrow Co      E° = -0.28 V

  1. 0.31
  2. 3.20
  3. 0.10
  4. 10.33

Question 211.0 pts

If E° for the disproportionation of Cu+(aq) to Cu2+(aq) and Cu(s) is +0.37 V at 25°C, calculate the equilibrium constant for the reaction.
  1. 3.2 x 1012
  2. 1.3 x 103
  3. 1.8 x 106
  4. 2.4 x 102

Question 221.0 pts

The standard potential of the cell:

Pb(s) | PbSO4(s) | SO42-(aq) || Pb2+(aq) | Pb(s)

is +0.23 V at 25°C. Calculate the equilibrium constant for the reaction of 1 M Pb2+(aq) with 1 M SO42-(aq).

  1. 7.7 x 103
  2. 8.0 x 1017
  3. 1.7 x 10-8
  4. 6.0 x 107

Question 231.0 pts

The standard voltage of the cell:

Ag(s) | AgBr(s) | Br-(aq) || Ag+(aq) | Ag(s)

is +0.73 V at 25°C. Calculate the equilibrium constant for the cell reaction.

  1. 2.2 x 1012
  2. 2.0 x 10-15
  3. 4.6 x 10-13
  4. 5.1 x 1014

Question 241.0 pts

The equilibrium constant for the reaction below:

2Hg(l) + 2Cl-(aq) + Ni2+(aq) \longrightarrow Ni(s) + Hg2Cl2(s)

is 5.6x10-20 at 25°C. Calculate the value of E°cell for this reaction.

  1. -1.14 V
  2. +1.14 V
  3. -0.57 V
  4. +0.57 V

Question 251.0 pts

You turn on a flashlight containing brand new NiCad batteries and keep it lit for a minute or two. Which of the following can be considered TRUE regarding the chemical state of these batteries?

I. \Delta G for the battery reaction is negative.

II. Ecell > 0

III. The batteries are at equilibrium.

IV. Ecell is substantially decreasing during this time.

  1. I and II only
  2. All but III
  3. All are true.
  4. III only
  5. All but IV

Question 261.0 pts

Which of the following batteries are rechargeable?

I. Alkaline Battery

II. NiMH Battery

III. Lithium Battery

IV. Lithium Ion Battery

V. Lead-Acid Battery

  1. I and III only
  2. II, IV, and V only
  3. II and V only
  4. All except I

Question 271.0 pts

Here is the discharge reaction for an alkaline battery:

Zn(s) + 2MnO2(s) + H2O(l)\longrightarrowZn(OH)2(s) + Mn2O3(s)

Which species is reduced as the battery is discharged?

  1. Mn2O3(s)
  2. H2O(l)
  3. Zn(s)
  4. MnO2(s)

Question 281.0 pts

What metal (in various oxidation states) is present at both the cathode and the anode in a typical car battery?
  1. lead
  2. cadmium
  3. lithium
  4. nickel
  5. zinc

Question 291.0 pts

The net redox reaction in a fuel cell is given below:

2H2 + O2 \longrightarrow H2O

What is the reaction at the anode in a fuel cell?

  1. H+ + OH- \longrightarrow H2O
  2. O2 \longrightarrow 2O2+ + 4e-
  3. O2 + 4e- \longrightarrow 2O2-
  4. H2 \longrightarrow 2H+ + 2e-

Question 301.0 pts

Which of the following is NOT an important characteristic of the proton exchange membrane (PEM) in a PEM fuel cell?
  1. It must withstand the high operating temperatures of the fuel cell.
  2. It is coated with catalysts that increase the rates of both the oxidation and reduction reactions.
  3. It physically separates the half-reactions.
  4. It must be stable in an acidic environment.
  5. It is permeable to protons.













CH302 · 50520 Principles of Chemistry II


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