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A LevelChemistryOCRExam Questions5. Physical Chemistry & Transition Elements (A Level Only)5.5 Redox & Electrochemistry

Redox & Electrochemistry (OCR A Level Chemistry)

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5.5 Redox & Electrochemistry

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5.5 Redox & Electrochemistry

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11 mark

Which row correctly describes oxidation and reduction in terms of the transfer of electrons and changes in oxidation state?

  Transfer of electrons Change in oxidation state
  oxidation reduction oxidation reduction
A gain loss increase decrease
B loss gain increase decrease
C loss gain decrease increase
D gain loss decrease increase

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    21 mark

    Which row describes the most common oxidation numbers of fluorine, oxygen and hydrogen in compounds?

      F O H
    A +7 -1 -1
    B +1 +2 +1
    C -7 -1 -1
    D -1 -2 +1

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      31 mark

      Below is a diagram of a voltaic cell. When the cell is running, what is happening in the salt bridge?

      electrochemical-cell-set-up-ocr-mcq

      • K+ ions flow to the zinc half-cell and NO3− ions flow to the copper half-cell

      • K+ ions flow to the copper half-cell and NO3− ions flow to the zinc half-cell

      • K+ and NO3− ions flow to the copper half-cell

      • K+ and NO3− ions flow to the zinc half-cell

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      41 mark

      Which is the correct equation to calculate electromotive force?

      • EӨcell = EӨreduction + EӨoxidation

      • EӨcell = EӨreduction – EӨoxidation

      • EӨcell = EӨhydrogen + EӨreduction

      • EӨcell = EӨoxidation – EӨreduction

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      51 mark

      Use the data below to help you answer this question.

      Half-equation

      Eθ / V

      Co3+ (aq) + e– ⇌ Co2+ (aq) 

      +1.82

      Cr3+ (aq) + e– ⇌ Cr2+ (aq)

      –0.41

      Fe3+ (aq) + e– ⇌ Fe2+ (aq)

      +0.77

      S2O82– (aq) + 2e– ⇌ 2SO42– (aq)

      +2.01

      Which is the most powerful oxidising agent from all the species in the table?

      • Co3+ (aq)

      • Cr3+ (aq)

      • Fe3+ (aq)

      • SO42– (aq)

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      11 mark

      Which reaction shows hydrogen behaving as an oxidising agent?

      • H2 + CuO → Cu + H2O

      • 2Na + H2 → 2NaH

      • H2 + Cl2 → 2HCl

      • C2H4 + H2 → C2H6

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      2
      Sme Calculator      1 mark

      1.50 g of impure iron wire was dissolved in 30 cm3 of sulfuric acid. The resulting iron(II) sulfate solution was made up to 250 cm3 with distilled water. 25.0 cm3 of the resulting solution was acidified and titrated with 0.020 mol dm-3 potassium manganate(VII) solution.

      20.0 cm3 of potassium manganate(VII) solution was required to reach the end-point of the titration.

      5Fe2+ (aq) + MnO4– (aq) + 8H+ (aq) → 5Fe3+ (aq) + Mn2+ (aq) + 4H2O (l)

      What is the percentage purity of the iron wire?

      • 7.44

      • 14.9

      • 74.4

      • 85.1

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      3
      Sme Calculator      1 mark

      A cell is constructed from the two redox systems below.

         Cu2+ (aq) + 2e– ⇌ Cu (s)   Eθ = +0.34 V

         Fe2+ (aq) + 2e– ⇌ Fe (s)   Eθ = -0.77 V

      Which statement(s) is / are correct for the cell?

      1. The cell potential is 1.11 V
      2. The reaction at the iron electrode is Fe (s) → Fe2+ (aq) + 2e– 
      3. The copper electrode increases in mass

      • 1, 2 and 3

      • Only 1 and 2

      • Only 2 and 3

      • Only 1

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      41 mark

      The redox equilibria for a hydrogen-oxygen fuel cell in acidic conditions are shown below.

         2H+ (aq) + 2e– ⇌ H2 (g)   Eθ = 0.00 V

         ½O2 (g) + 2H+ (aq) + 2e– ⇌ H2O (l)   Eθ = +1.23 V

      What is the equation for the overall cell reaction?

      • ½O2 (g) + 4H+ (aq) + 4e– → H2 (g) + H2O (l)

      • H2 (g) + H2O (l) → ½O2 (g) + 4H+ (aq) + 4e– 

      • H2O (l) → H2 (g) + ½O2 (g)

      • H2 (g) + ½O2 (g) → H2O (l) 

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      5
      Sme Calculator      1 mark

      A cell is constructed from the two redox systems below.

         Sn2+ (aq) + 2e– ⇌ Sn (s)   Eθ = -0.14 V

         Fe3+ (aq) + e– ⇌ Fe2+ (aq)   Eθ = +0.77 V

      What is the value of the electromotive force, in V?

      • -0.91

      • +0.63

      • +1.68

      • +0.91

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      61 mark

      Which descriptions about the different systems used in batteries / cells are correct?

        Lead-acid Nickel-cadmium Hydrogen-oxygen
      A Fuel Rechargeable Fuel
      B Rechargeable Fuel Rechargeable
      C Fuel Fuel Rechargeable
      D Rechargeable Rechargeable Fuel

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        71 mark

        The overall equation for iodine-thiosulfate titrations is shown below.

        2S2O32- (aq) + I2 (aq) → 2I– (aq) + S4O62- (aq)

        Which statement(s) is / are correct for iodine-thiosulfate titrations?

        1. Starch is added as an indicator at the start of the titration
        2. The thiosulfate ion acts as a reducing agent
        3. Iodine-thiosulfate titrations can be used to determine the copper content in alloys

        • 1, 2 and 3

        • Only 1 and 2

        • Only 2 and 3

        • Only 1

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        11 mark

        If a dilute acid is added to an aqueous solution containing nitrate ions, NO2-, two different nitrogen compounds are released as gases.

        2H+ (aq) + 2NO2- (aq) rightwards arrow H2O (l) + NO (g) + NO2 (g)

        Which of the three statements below correctly describe(s) the process?

        1. The H+ (aq) ion is oxidised by NO2- (aq)

        2. Some nitrogen atoms are oxidised, and some nitrogen atoms are reduced

        3. The H+ (aq) ion acts as a catalyst

        • 1 and 2 only

        • 2 only

        • 2 and 3 only

        • 1, 2 and 3

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        21 mark

        A voltaic cell consisting of zinc and silver is set up. The following overall reaction takes place:

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

        What are the correct half-equations at each electrode?

         

        Anode (negative electrode)

        Cathode ( positive electrode)

        A

        Ag (s) → Ag+ (aq)  + e-

        Zn2+ (aq) + 2e- → Zn (s)

        B

        Ag+ (aq)  + e- → Ag (s) 

        Zn (s) → Zn2+ (aq) + 2e-

        C

        Zn (s) → Zn2+ (aq) + 2e-

        Ag+ (aq)  + e- → Ag (s) 

        D

        Zn2+ (aq) + 2e- → Zn (s)

        Ag (s) → Ag+ (aq)  + e-

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          31 mark

          Below are four descriptions about the movements of electrons in voltaic cells.

          Which is the correct statement?

          • Electrons flow through the external wire from the cathode (positive electrode) to the anode (negative electrode)

          • Electrons flow through the external wire from the anode (negative electrode) to the cathode (positive electrode)

          • Electrons flow through the salt bridge from the oxidizing agent to the reducing agent

          • Electrons flow through the salt bridge from the reducing agent to the oxidizing agent

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          41 mark

          Some standard electrode potential data is shown in the table.

          Electrode half-equation 

          EӨ / V

          Co3+ (aq) + e– → Co2+ (aq) 

          +1.82

          Cu2+ (aq) + 2e- ⇋ Cu (s) 

          +0.34

          Fe3+ (aq) + e– → Fe2+ (aq)

          +0.77

          I2 (s) + 2e– → 2I– (aq) 

          +0.54

          S2O82– (aq) + 2e– → 2SO42– (aq)

          +2.01

          Which species cannot catalyse the reaction between iodide ions, I– (aq), and peroxodisulfate ions, S2O82– (aq)?

          • Co2+

          • Cu2+

          • Fe3+

          • Fe2+

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          51 mark

          What happens to the hydrogen in a hydrogen-oxygen fuel cell?

          • It is oxidised at the cathode

          • It is reduced at the cathode

          • It is oxidised at the anode

          • It is reduced at the anode

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