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International A LevelChemistryEdexcelExam Questions5: Transition Metals and Organic Nitrogen Chemistry5.1 Redox Equilibria

Redox Equilibria (Edexcel International A Level Chemistry)

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5.1 Redox Equilibria

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5.1 Redox Equilibria

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11 mark

The standard hydrogen electrode uses an electrode of platinum coated in a finely divided form of the metal called platinum black.

What is the purpose of this coating?

  • to increase the rate of the equilibrium between the hydrogen gas and the hydrogen ions

  • to provide an inert protective coating for the electrode

  • to increase the electrical conductivity of the electrode

  • to ensure that the conditions remain standard

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1a1 mark

The apparatus shown was used to measure the standard electrode potential for the reduction of Cr2straight O subscript 7 superscript 2 minus end superscript ions to Cr3+ ions in acid solution:

Cr2straight O subscript 7 superscript 2 minus end superscript(aq) + 14H+(aq) + 6e–→ 2Cr3+(aq) + 7H2O(l)

q1-paper-5-oct-2021-edexcel-ial-chemistry

a)
Which material should be used for each electrode?

      Electrode 1 Electrode 2
  ☐ A Na2Cr2O7 Cr2O3
  ☐ B H2 Cr
  ☐ C Pt Cr
  ☐ D Pt Pt

    Choose your answer

    1b1 mark
    b)
     Solution 1 is

    • 0.33 mol dm–3 H3PO4 (aq)

    • 0.50 mol dm–3 H2SO4 (aq)

    • 1.00 mol dm–3 HCl (aq)

    • 1.00 mol dm–3 CH3COOH (aq)

    Choose your answer

    1c
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    c)
    Solution 2 contains 14.71g of K2Cr2O7 .

    What mass of Cr2(SO4)3⋅18H2O should also be used?

    [Mr values: K2Cr2O7 = 294.2 Cr2(SO4)3⋅18H2O = 716.3]

    • 8.95 g

    • 17.91 g

    • 19.62 g

    • 35.82 g

    Choose your answer

    1d1 mark
    d)
    Solution 2 is best acidified with

    • H2SO4

    • HCl

    • HBr   

    • H2CrO4

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    2a1 mark

    A hydrogen‐oxygen fuel cell is used to provide electrical energy for an electric motor in a car.

    a)
    The electrolyte in the fuel cell is acidic. What is the half‐equation at the anode?

    • 1⁄2O2 (g) + 2H+ (aq) + 2e−→ H2O (l)

    • H2O (l) → 1⁄2O2 (g) + 2H+ (aq) + 2e−

    • H2 (g) → 2H+ (aq) + 2e−

    • 2H+ (aq) + 2e−→ H2 (g)

    Choose your answer

    2b1 mark
    b)
    Hydrogen‐oxygen fuel cells have advantages over methanol‐oxygen fuel cells in vehicles.

    Which of these is an advantage of the hydrogen‐oxygen fuel cell?

    • more energy is released per mole of fuel used

    • emissions do not contribute to climate change

    • hydrogen is easier to store than methanol

    • only hydrogen can be obtained from renewable resources

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    31 mark

    The equation for a redox reaction is

    5Fe2+(aq) + Mnbegin mathsize 16px style O subscript 4 to the power of minus sign end style(aq) + 8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)

    Which is the correct cell diagram to measure Eθcell for this reaction?

    • Fe | Fe2+, Fe3+ || [MnO4– + 8H+], [Mn2+ + 4H2O] | Mn

    • Fe | Fe2+, Fe3+ || [Mn2+ + 4H2O], [MnO4– + 8H+] | Mn

    • Pt | Fe2+, Fe3+ || [MnO4– + 8H+], [Mn2+ + 4H2O] | Pt

    • Pt | Fe2+, Fe3+ || [Mn2+ + 4H2O], [Mnstraight O subscript 4 superscript minus+ 8H+] | Pt

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    4a
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    This question is about the reaction

    2Fe3+ (aq) + Ti (s) → 2Fe2+ (aq) + Ti2+ (aq)        E subscript cell superscript ⦵ space equals space plus 2.40 straight V

    a)
    The electrode potential for the Fe3+/ Fe2+ electrode system is +0.77 V.

    What is the electrode potential for the Ti2+/Ti electrode system?

    • −3.17V

    • −1.63V

    • +1.63V

    • +3.17V

    Choose your answer

    4b1 mark

    What metals should be used for the electrodes in the cell for this reaction?

        Metals used for the electrode
        Fe3+/ Fe2+ electrode system Ti2+/ Ti electrode system
    □ A iron titanium
    □ B iron platinum
    □ C platinum titanium
    □ D platinum platinum

      Choose your answer

      4c
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      c)
      The half-cell for the Fe3+/ Fe2+ electrode system is prepared by mixing equal volumes of solutions of iron(II) sulfate, FeSO4, and iron(III) sulfate, Fe2(SO4)3.

      What concentrations of the original solutions are needed for the resulting mixture to be standard?

          Concentration of the original solution
          FeSO4 Fe2(SO4)3
      □ A 1 mol dm–3 0.5 mol dm–3
      □ B 1 mol dm–3 1 mol dm–3
      □ C 2 mol dm–3 1 mol dm–3
      □ D 2 mol dm–3 2 mol dm–3

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        5a1 mark

        An electrochemical cell is set up to measure E subscript cell superscript ⦵ for the reaction

        Fe (s) + Sn2+ (aq) → Fe2+ (aq) + Sn (s)

        a)
        What is the cell diagram for this cell?

        • Fe(s) | Fe2+(aq) || Sn(s) | Sn2+(aq)

        • Fe2+(aq) | Fe(s) || Sn2+(aq) | Sn(s)

        • Fe(s) | Fe2+(aq) || Sn2+(aq) | Sn(s)

        • Fe2+(aq) | Fe(s) || Sn(s) | Sn2+(aq)

        Choose your answer

        5b
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        b)
        The standard electrode potential for the Fe / Fe2+ electrode system is −0.44 V and E subscript cell superscript ⦵ for the reaction is +0.30 V.

        What is the standard electrode potential for the Sn / Sn2+ electrode system?

        • −0.74 V

        • −0.14 V

        • +0.14 V

        • +0.74 V

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        61 mark

        Hydrogen-oxygen fuel cells can operate in acidic or alkaline conditions.

        What is the reaction at the anode in an alkaline hydrogen-oxygen fuel cell?

        • O2 (g) + 2H2O (l) + 4e− → 4OH− (aq)

        • 4OH− (aq) → O2 (g) + 2H2O (l) + 4e−

        • 2H2O (l) + 2e− → H2 (g) + 2OH− (aq)

        • H2 (g) + 2OH− (aq) → 2H2O (l) + 2e−

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        1a1 mark

        An electrochemical cell is made from the electrode systems shown by these half‐equations.

           Ag+ (aq) + e−       ⇌  Ag (s)      E to the power of ⦵ = +0.80V

          Vbegin mathsize 16px style O subscript 2 to the power of plus sign end style (aq) + 2H+ (aq) + e−       ⇌  VO2+ (aq) + H2O (l)   E to the power of ⦵= +1.00V

        The apparatus used to measure the value for space E subscript cell space end subscript superscript ⦵ under standard conditions is shown.

        q3-paper-5-jan-2022-edexcel-ial-chemistry

        a)
        Which silver compound could be used as the electrolyte in the left‐hand half‐cell?

        • silver nitrate

        • silver hydroxide

        • silver chloride

        • silver carbonate

        Choose your answer

        1b1 mark
        b)
        The electrolyte in the right‐hand half‐cell is prepared using equal volumes of

        • 1 mol dm−3 acidified VO2+ (aq) and 1 mol dm−3 acidified VO2+ (aq)

        • 2 mol dm−3 acidified VO2+ (aq) and 2 mol dm−3 acidified VO2+ (aq)

        • 1 mol dm−3 VO2+ (aq) and 1 mol dm−3 HCl (aq)

        • 1 mol dm−3 VO2+ (aq) and 1 mol dm−3  HCl (aq)

        Choose your answer

        1c1 mark
        c)
        Which is the equation for the overall cell reaction under standard conditions?

        • VO2+(aq) + Ag+(aq) + H2O(l) rightwards arrow begin mathsize 16px style V O subscript 2 to the power of plus sign open parentheses aq close parentheses end style + Ag(s) + 2H+(aq)

        • VO subscript 2 superscript plus left parenthesis aq right parenthesis + Ag(s) + 2H+(aq) rightwards arrowVO2+(aq) + Ag+(aq) + H2O(l) 

        • VO2+(aq) + 3Ag(s) + 2H+(aq) rightwards arrow VO subscript 2 superscript plus left parenthesis aq right parenthesis + 3Ag+(aq) + H2O(l)

        • VO subscript 2 superscript plus left parenthesis aq right parenthesis + 3Ag+(aq) + H2O(l) rightwards arrowVO2+(aq) + 3Ag(s) + 2H+(aq)

        Choose your answer

        1d
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        d)
        Which is the value of E subscript cell superscript ⦵ in volts?

        • −1.80

        • −0.20

        • +0.20

        • +1.80

        Choose your answer

        1e1 mark

        Which is the cell diagram for this cell, using the conventional representation of half‐cells?

        • Ag(s) | Ag+(aq) || [ begin mathsize 16px style V O subscript 2 to the power of plus sign open parentheses aq close parentheses end style + 2H+(aq)] | [VO2+(aq) + H2O(l)] | Pt(s)

        • Ag(s) | Ag+(aq) || [ VO subscript 2 superscript plus open parentheses aq close parentheses + 2H+(aq)] , [VO2+(aq) + H2O(l)] | Pt(s)

        • Ag(s) | Ag+(aq) || [ VO2+(aq)  + H2O(l)] | [begin mathsize 16px style V O subscript 2 to the power of plus sign open parentheses aq close parentheses end style + 2H+(aq)] | Pt(s)

        • Ag(s) | Ag+(aq) || [ VO2+(aq)  + H2O(l)] , [begin mathsize 16px style V O subscript 2 to the power of plus sign open parentheses aq close parentheses end style + 2H+(aq)] | Pt(s)

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        21 mark

        Some standard electrode potentials are shown.

        Electrode system E to the power of ⦵ / V
        Bk3+ + e– ⇌ Bk2+ –2.80
        Cu2+ + e– ⇌ Cu+ +0.15
        Bk4+ + e– ⇌ Bk3+ +1.67
        Au+ + e– ⇌ Au +1.69
        Au2+ + e– ⇌ Au+ +1.80
        Ag3+ + e– ⇌ Ag2+ +1.80
        Ag2+ + e– ⇌ Ag+ +1.98
        Cu3+ + e– ⇌ Cu2+ +2.40


        Which of these disproportionation reactions is thermodynamically feasible under standard conditions?

        • 2Bk3+ → Bk2+ + Bk4+

        • 2Cu2+ → Cu++ Cu3+

        • 2Au+ → Au + Au2+

        • 2Ag2+ → Ag++ Ag3+

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        31 mark

        Which is true of a hydrogen‐oxygen fuel cell?

        • the cathode has a more positive potential than the anode

        • hydrogen is oxidised at the cathode

        • oxygen is reduced at the negative electrode

        • the cell potential is different when operating under alkaline or acidic conditions

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