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CHEM 124 > CHEM 124 Ch. 21(3,4,7) > Flashcards

CHEM 124 Ch. 21(3,4,7) Flashcards

Relative redox strength, Gibbs energy and cell potential, and electrolysis

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1
Q

Given Ni2+ (aq) + 2e– → Ni (s), classify each species according to its ability to act as an oxidizing or reducing agent.
Ni2+ (aq)
Ni (s)

  • reducing agent
  • oxidizing agent
A

Ni2+ (aq): oxidizing agent
Ni (s): Reducing agent

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2
Q

If a substance acts as a strong oxi agent, it will appear on a table of standard reduction potentials as the ____ in a 1/2 reaction w/ a ____ standard reduction potential.

  • reactant; negative
  • reactant; positive
  • product; positive
  • product; negative
A
  • reactant; positive
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3
Q

As listed in the table of standard electrode potentials, the reactant in the 1/2 reactions are potentials ___ agents, while the products of the 1/2 reactions are potential ____ agent.

  • oxidizing; reducing
  • reducing; oxidizing
A
  • oxidizing; reducing
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4
Q

Given that the redox Fe (s) + 2Ag+ (aq) → Fe2+ (aq) + Ag (s) occurs spontaneously as written, match each species w/ the appropriate identification.
Fe(s)->
Ag+(aq)->
Fe2+->
Ag(s)->

  • weaker oxidizing agent
  • stronger reducing agent
  • weaker reducing agent
  • stronger oxidizing agent
A

Fe(s)-> Stronger RA
Ag+(aq)-> Stronger OA
Fe2+(aq)-> Weaker OA
Ag(s)-> Weaker RA

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5
Q

When predicting the spon. reaction btwn 2 different 1/2 cells, the reaction w/ the most negative cell potential will be the ____ reaction, while the reaction w/ the most positive cell potential will be the ____ reaction.

  • oxi;red
  • red; oxi
A
  • oxi;red
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6
Q

A species acts as a(n) ____ agent if it gains e- in a 1/2 reaction. Converesley, it could potentially act as a(n) ____ agent if it loses e- in a 1/2 reaction

  • oxi;red
  • red;oxi
A
  • oxi;red
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7
Q

Given that the standard potential for Ag+ (aq) + e– → Ag (s) is +0.80 V, find the standard reaction potential for 2Ag+ (aq) + 2e– → 2Ag (s).

  • .64V
  • .8 V
  • 1.6 V
  • -.8 V
A
  • .8V
    Reason: Std cell potentials are intensive so changing the substance quantity doesn’t change the cell potential.
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8
Q

If a substance acts as a strong red agent, it will appear on a table of standard reduction potentials as the ____ in a 1/2 reaction w/ a ____ standard reduction potential.

  • reactant; negative
  • reactant; positive
  • product; positive
  • product; negative
A
  • product; negative
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9
Q

Ag+ (aq) + e– → Ag (s); Eo = +0.799 V
Co2+ (aq) + 2e– → Co (s); Eo = –0.277 V
Fe2+ (aq) + 2e– → Fe (s); Eo = –0.440 V
Rank the species in order of increasing strength to act as an reducing agent from weakest to strongest

  • Fe(s)
  • Co (s)
  • Ag (s)
A

In order: Ag<Co<Fe
Reason: the more negative the value the stronger the RA is ( or less likely to be oxidized as it get’s stronger)

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10
Q

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

  • The reactants in a half-reaction with a positive standard cell potential will always be reduced in an electrochemical cell.
  • If Eo for a given half-reaction is large and positive, the reaction is spontaneous from left to right as written.
  • The best reducing agents will be reactants with the most negative cell potentials.
  • The best oxidizing agents will be reactants in half-reactions with the most positive cell potentials.
A
  • If Eo for a given half-reaction is large and positive, the reaction is spontaneous from left to right as written.
  • The best oxidizing agents will be reactants in half-reactions with the most positive cell potentials.
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11
Q

What is the spon reaction that occurs when the 2 1/2 cells are combined?
Fe3+ (aq) + e– → Fe2+ (aq); Eo = 0.77 V
Ag+ (aq) + e– → Ag (s); Eo = 0.80 V

  • Fe2+ (aq) + Ag (s) → Fe3+ (aq) + Ag+ (aq)
  • Ag (s) + Fe3+ (aq) → Ag+ (aq) + Fe2+ (aq)
  • Ag+ (aq) + Fe3+ (aq) → Fe2+ (aq) + Ag (s)
  • Ag+ (aq) + Fe2+ (aq) → Ag (s) + Fe3+ (aq)
A
  • Ag+ (aq) + Fe2+ (aq) → Ag (s) + Fe3+ (aq)
    Reason: reaction that’s the most negative/ least positive reduction potential is reversed.
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12
Q

True or False: For a spon redox reaction, the products are stronger oxi and red agents than the reactants

A

False
Reason: The strongest agents are reactants on spon reactions

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13
Q

Ag+ (aq) + e– → Ag (s); Eosilver = +0.799 V. A high, positive reduction potential for a metal cation like Ag+ indicated that silver metal is ____ active.

  • very
  • not very
A

Not very
Reason: the lower it is the stronger the RA (it’s higher up)

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14
Q

Given the 2 1/2 reactions,
Cr3+ + 3e– → Cr; Eo = –0.74 V
Ni2+ + 2e– → Ni; Eo = –0.28 V
which reaction will be the reduction reaction in the spon reaction that would occur btwn them?

  • Ni2+ + 2e– → Ni
  • Cr3+ + 3e– → Cr
  • Ni → Ni2+ + 2e–
  • Cr → Cr3+ + 3e–
A
  • Ni2+ + 2e– → Ni
    Reason: most positive cell potential
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15
Q

Given that the std. potential for Ca2+ (aq) + 2e– → Ca (s) is –2.87 V, what is the std. potential for 2Ca2+ (aq) + 4e– → 2 Ca (s)?

  • 8.24 V
    – -5.74 V
    – -2.87 V
A
  • -2.87 V
    Reason: changing the coefficient’s don’t change the Eo 1/2 cell
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16
Q

K+ (aq) + e– → K (s); Eo = –2.925 V
Hg2+ (aq) + 2e– → Hg (l); Eo = +0.854 V
I2 (s) + 2e– → 2I– (aq); Eo = +0.536 V
Rank the species in order of increasing strength to act as an oxidizing agent from weakest to strongest

  • K+(aq)
  • Hg2+ (aq)
  • I2 (s)
A

K+<I2<Hg2+

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17
Q

Consider:
Cu (s) → Cu2+ (aq) + 2e–; Eo = –0.337 V
Cd (s) → Cd2+ (aq) + 2e–; Eo = 0.403 V
Ag (s) → Ag+ (aq) + e–; Eo = –0.799 V
What’s the most active metal?

  • Cd
  • Cu
  • Ag
A
  • Cd
    Reason: The weaker the RA the more likely it can be oxi
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18
Q

What’s the spon reaction that occurs when Zn2+ (aq) + 2e– → Zn (s); Eo = –0.76 V
Na+ (aq) + e– → Na (s); Eo = –2.71 V are combined.

  • 2Na (s) + Zn2+ (aq) → 2Na+ (aq) + Zn (s)
  • Na (s) + Zn2+ (aq) → Na+ (aq) + Zn (s)
  • 2Na+ (aq) + Zn (s) → 2Na (s) + Zn2+ (aq)
  • Na+ (aq) + Zn (s) → Na (s) + Zn2+ (aq)
A
  • 2Na (s) + Zn2+ (aq) → 2Na+ (aq) + Zn (s)
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19
Q

The Faraday constant is the charge (in coulombs) of

  • any and all electrons when ΔG = 0.00
  • one electron
  • one gram of electrons
  • one mole of electrons
A
  • one mole of electrons
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20
Q

Highly active metals are easily ____. Therefore, they are generally found as products in the 1/2 reactions with ___ std. reduction potentials.

  • reduced; negative
  • oxidized; positive
  • oxidized; negative
  • reduced; positive
A
  • oxidized; negative
    Reason: lower the metal= stringer RA. If Eocell for H+ reduction is more + w/ metal A than B, metal A is s stronger RA and is a active metal
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21
Q

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

  • more negative; smaller
  • more negative; larger
  • more positive; smaller
  • more positive; larger
A
  • more positive; smaller
    Reason: Eo and gibbs free are inverses of each other. AG get’s more + Keq is smaller
22
Q

If ΔGo < 0, the reaction is ____ as written: K<1, the reaction is ____ as written.

  • spontaneous; spontaneous
  • spontaneous; nonspontaneous
  • nonspontaneous; spontaneous
  • nonspontaneous; nonspontaneous
A
  • spontaneous; nonspontaneous
    Reason: If K < 1, the reaction favors the reactants and will therefore not be spontaneous as written.
23
Q

The Nernst equation is used to find the cell potental 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).

A

nonstandard; quotient

24
Q

Rank the following metals in order of decreasing activity based on the information given. Place the MOST active metal at the top of the list.

Ag+ + e– → Ag; Eo = 0.799 V
Cd+2 + 2e– → Cd; Eo = –0.403 V
Sn2+ + 2e– → Sn; Eo = –0.136 V

  • Cd
  • Sn
  • Ag
A

In that order

25
Q

The Farday’s constant allows 1 to convert btwn moles of ____ and the equivalent amount of charge in units of ____.

A

electrons; coulombs

26
Q

Common forms of ____ are:
E = Eo – 0.0592V/n log Q (at 298 K)
E = Eo – RTnF ln Q

  • the standard cell potential
  • the Faraday constant
  • the standard free energy of an electrochemical cell
  • the Nernst equation
A
  • the Nernst equation
27
Q

Free energy is related to the cell potential through ΔG = –nFE. Match each symbol in this equation to the correct quantity.
n->
F->
E->

  • Cell potential
  • Moles of e- exchanged in overall reaction
  • Faraday constant
A

n-> Moles of e- exchanged in overall reaction
F-> Faraday constant
E-> Cell potential

28
Q

1 mol of Zn and 0.500 moles of Zn2+ ions in 1 L of solution are used to form one half-reaction cell, while 2 moles of Cu and 3 moles of Cu+ in 1 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 = 0.87 V
  • Q = 0.167
  • E= 0.95 V
  • Q = 0.222
  • Q = 0.0556
A
  • Q = 0.0556
  • E= 0.95 V
29
Q

If DeltaGo for a reaction is = to 0, what must be true regarding the =m constant?

  • K<0
  • K=0
  • K<1
  • K=1
A
  • K=1
    Reason:
    Spon: DeltaGo<0, K>1, Eocell>0
    At Equilibrium: DeltaGo=0, K=1, Eocell=0
    Nonspon: DeltaGo>0, K<1, and Eocell<0
30
Q

Match the relative values of Q and K to the associated values of the nonstandard cell potential
Q<K ->
Q=K ->
Q>K ->

  • Ecell<0
  • Ecell=0
  • Ecell >0
A

Q<K -> Ecell>0
Q=K -> Ecell=0
Q>K -> Ecell <0

31
Q

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
  • ΔGo
  • Q, the reaction coefficient
  • q, the heat change for the reaction
A
  • n (the number of electrons in the balanced reaction)
  • E°, the standard cell potential
  • Q, the reaction coefficient
32
Q

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

A

concentration

33
Q

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 – RT/nF log Q
  • E = Eo – 0.0592/n ln Q
  • E = Eo – 0.0592V/n log Q (at 298 K)
  • E = Eo – RT/nF ln Q
  • E = Eo + RT/nF ln Q
A
  • E = Eo – RT/nF ln Q
  • E = Eo – 0.0592V/n log Q (at 298 K)
34
Q

True or False: The emf of a concentration cell is derived from a concentration gradient wherein the less concentrated cell acts as the anode and the more concentrated cell acts as the cathode.

A

True

35
Q

Ecell = Ecello – RT/nF ln Q
Based on the Nernst equation, how does the magnitude of Q affect the cell potential (reactant </>/= product)?
Q<1->
Q>1->
Q=1->

  • Ecell<Ecello
  • Ecell>Ecello
  • Ecell=Ecello
A

Q<1->Ecell>Ecello
Q>1->Ecell<Ecello
Q=1->Ecell=Ecello

36
Q

Calculate Ecell for the concentration cell:Zn (s)|Zn2+ (aq, 0.100 M)||Zn2+ (aq, 1.00 M)|Zn (s)

  • –0.030 V
  • +0.059 V
  • –0.059 V
  • +0.030 V
A
  • +.030
37
Q

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
  • Ecell < Ecello
  • Ecell ≈ Ecello
A

Ecell > Ecello

38
Q

Select applications for concentration cells. Select all that apply.

  • Ion-selective electrodes
  • pH meters
  • Nerve cell membranes
  • Primary batteries
  • Rechargeable batteries
A
  • pH meters
  • Ion-selective electrodes
  • Nerve cell membranes
39
Q

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

A

electrolysis

40
Q

Select the statements that correctly describe a concentration cell. Select all that apply.

  • The cell emf is generated because of a difference in concentration.
  • A concentration cell spontaneously generates electricity.
  • The electrode and the electrolyte are the same materials in both half-cells.
  • The electrode and the electrolyte may be different materials as long as the electrolytes are at different concentrations.
  • The anode and cathode half-cells cannot reach the same concentration.
A
  • The electrode and the electrolyte are the same materials in both half-cells
    The cell emf is generated because of a difference in concentration.
  • A concentration cell spontaneously generates electricity.
41
Q

Match each type of electrochemical cell w/ the appropriate description.
For a voltaic cell->
For an electrolytic cell ->
Nonspon ->
Spon->

  • electrolytic cell
  • voltaic cell
  • DeltaG>0
  • DeltaG<0
A

For a voltaic cell-> DeltaG<0
For an electrolytic cell -> DeltaG>0
Nonspon -> electrolytic cell
Spon-> voltaic cell

42
Q

If one were to construct an electrochemical cell consisting on 2 Zn2+/Zn at 2 different conc., the more conc, cell will be the ____.

  • Cathode
  • Anode
A

Cathode
Reason: the anode (diluted) is more concentrated (ions in the solution). The cathode (concentrated) is the opposite.

43
Q

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

  • volt; min
  • coulombs; min
  • volts; sec
  • coulumbs; sec
A
  • coulumbs; sec
44
Q

A concentration cell: Ag+ (1.0 M) + Ag (s) → Ag (s) + Ag+ (x M). When a silver electrode is immersed into this cell at 25C and it is tested against a 1M AgNO3/Ag electrode, a .250-V cell potential develops. Calculate the concentration of the electrolyte in the anode compartment.
E = E°cell – 0.0592/n log Q

  • 1.47 x 10–2 M
  • 6.03 x 10–5 M
  • 1.67 x 104 M
  • 3.58 x 10–9 M
A
  • 6.03 x 10–5 M
    Reason: .250 = 0 – 0.0592/1 log x/1= –0.0592 log x
    log x: –(0.2500/.0592)= –4.22
    x = 10^–4.22 = 6.03 x 10–5
45
Q

pH meters, ion selective electrodes, and nerve cells are all examples of the application of ____.

A

concentration

46
Q

When Ca^2+ are electrolytically reduced to Ca(s), what is the relationship btwn the moles of e- transferred and the moles of Ca(s) produced?

  • 2 mol of e– will be transferred for every 1 mol Ca (s) produced.
  • The ratio of electrons to Ca (s) is 1:1.
  • 1 mol of e– will be transferred for every 2 mol Ca (s) produced.
A
  • 2 mol of e– will be transferred for every 1 mol Ca (s) produced.
47
Q

Match each electrode in an electrolytic cell.
Oxi ->
Red->

  • Anode
  • Cathode
A

Oxi -> anode
Red-> cathode

48
Q

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 sec at using a current of 2.0 A?

  • (2.0A)(40.1g/mo) / (96,500C/1mol e−)(2mol e−/1mol Ca)(30s)
  • (2.0A)(30.0s)(40.1g Ca/mol Ca) / (96,500C/1mol e−)(2mol e/−1mol Ca)
  • (96,500C/1mol e−)(2mol e−/1mol Ca) / (2.0A)(30s)(40.1g/mo)
A
  • (2.0A)(30.0s)(40.1g Ca/mol Ca) / (96,500C/1mol e−)(2mol e/−1mol Ca)
49
Q

A(n) ____ cell exploits a spon redox reaction to generate electricity, whereas a(n) ____ cell required a cont. electricity.

  • electrolytic; voltaic
  • voltaic; electrolytic
A
  • voltaic; electrolytic
50
Q

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
  • C = V x s
  • C = A×s/F
A
  • current (A) = charge/time
  • C = A x s
51
Q

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

  • The total charge is 2 x 96,500 = 1.93 x 10^5 C.
  • 3 mol e– per mole of Cr (s)
  • 2 mol e– per mole of Cr (s)
  • The total charge is 3 x 96,500 = 2.90 x 10^5 C.
  • The total charge is 96,500/3= 3.22 x 10^4 C.
A
  • 3 mol e– per mole of Cr (s)
  • The total charge is 3 x 96,500 = 2.90 x 10^5 C.
52
Q

It is easy to forget to consider the number of e- that take part in an electrochemical reaction when solving for the product of electrolysis. If 6 moles of e- are consumed during the reduction of Fe3+ to form Fe (s), how many moles of iron are formed?

  • 2 moles Fe
  • 1 mole Fe
  • 6 moles Fe
  • 3 moles Fe
A
  • 2 moles Fe
    Reason: It takes 3 mol of e- to make 1 mol of Fe

CHEM 124 (4 decks)

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