Syllabus Edition

First teaching 2014

Last exams 2024

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Redox Processes (DP IB Chemistry: SL)

Exam Questions

3 hours46 questions
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

B

C

D

gain

loss

loss

gain

loss

gain

gain

loss

increase

increase

decrease

decrease

decrease

decrease

increase

increase

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    21 mark

    The heptahydrate mineral of magnesium sulfate is used in Epsom Salts for preparing therapeutic baths. Magnesium sulfate is also used in some medical applications.

    What is the oxidation state of MgSO4?

    • -2

    • +2

    • +7

    • 0

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    31 mark

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

     

    F

    O

    H

    A

    B

    C

    D

    +7

    +1

    -7

    -1

    -1

    +2

    -1

    -2

    -1

    +1

    -1

    +1

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      41 mark

      Solutions containing chlorate(I) ions decompose on heating as shown:                    

                  3ClO-  →  ClO3- + 2Cl- 

      Which row is correct for the oxidation state of the chlorine in each ion? 

       

      ClO-

      ClO3-

      Cl-

      A

      B

      C

      D

      +1

      +1

      -1

      -1

      +5

      +3

      +5

      +3

      -1

      +1

      -1

      +1

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        51 mark

        A student added a solution of iodine to a solution of sodium bromide. Which statement correctly describes what happens?

        • No reaction occurs

        • The bromide ions are oxidised

        • The iodine atoms are oxidised

        • Both the bromide and iodide ions undergo changes in their oxidation state

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        61 mark

        In which of the following reactions is the change in oxidation number the smallest for nitrogen?

        • N2 + 3H2 → 2NH3

        • 3Mg + N2 → Mg3N2

        • 4NH3 + 5O2 → 4NO + 6H2O

        • 2NO + O2 → 2NO2

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        71 mark

        In the compound [ICl2]+[SbCl6], the oxidation number of chlorine is −1.

        What are the oxidation numbers of I and Sb in the compound?

         

        I

        Sb

        A

        B

        C

        D

        +1

        +1

        +3

        +3

        +5

        +7

        +5

        +7

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          81 mark

          Titanium dioxide is obtained from the ore ilmenite, Fe(II)TiO3

                                         FeTiO3 → TiO2 

          What is the change in the oxidation number of titanium in the reaction?

          • +4 to +5

          • +3 to +4

          • No change in oxidation number occurs

          • +6 to +4

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          91 mark

          Below are four statements about voltaic and electrolytic cells. Identify the statement that is correct for voltaic cells but not for electrolytic cells

          • An electrolyte is needed in the cell

          • Ions are moving in the electrolyte

          • Oxidation occurs at the anode

          • Electrons flow from the negative to the positive electrode 

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          101 mark

          What substance will be obtained at the positive electrode (anode) when molten KBr is electrolysed?

          • K(l)

          • Br(l)

          • Br2(l)

          • K(s)

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          11 mark

          Oxidation numbers can be used to balance equations. Chlorine and hot aqueous sodium hydroxide react to produce chloride ions, chlorate ions and water. 

          What are the values of the coefficients p, r and s in the equation?                                     

                               pCl2(g) + qOH-(aq)  →  rCl-(aq) + sClO3-(aq) + tH2O(l) 

           

          p

          r

          s

          A

          B

          C

          D

          3

          3

          2

          2

          5

          6

          5

          4

          1

          2

          1

          2

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            21 mark

            The chemistry of the Group VII elements often involves redox processes.

            Which of the following statements is correct?

            • Bromine can oxidise chloride ions

            • Iodide ions are the weakest reducing agent of the first four Group VII ions

            • In reactions with water, chlorine is oxidised and reduced

            • Fluorine is a weaker oxidising agent than chlorine

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            31 mark

            Four reactions are shown below. In which reaction is the species shown in bold acting as an oxidising agent?

            • Cr2O72- + 8H+ + 3SO32- → 2Cr3+ + 4H2O + 3SO42-

            • Mg + Fe2+ → Mg2+ + Fe

            • Cl2 + 2Br- → 2Cl- + Br2

            • Fe2O3 + 3CO → 2Fe + 3CO2

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            41 mark

            In which compound are there two different elements with the same oxidation number?

            • Mg(OH)2

            • Na2SO4

            • HClO

            • NH4Cl

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            51 mark

            When sulfuric acid and sodium iodide react, one of the reactions that takes place is shown by the equation below: 

                        8NaI  +  9H2SO4  →  8NaHSO4  +  4I2  +  H2S  +  4H2

            Which species has been oxidised in this reaction?

            • I

            • SO42−

            • Na+

            • H+

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            61 mark

            The following reaction can be used to determine the mass of titanium dioxide in an ore. 

                        3TiO2  +  4BrF3  →  3TiF4  +  2Br2  +  3O2 

            Which element increases in oxidation number in this reaction?

            • fluorine

            • bromine

            • titanium

            • oxygen

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            71 mark

            In which reaction does hydrogen behave as an oxidizing agent?

            • 2Na  +  H2  →  2NaH

            • N2  +  3H2  →  2NH3 

            • H2  +  Cl2  →  2HCl

            • C2H4  +  H2  →  C2H6

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            81 mark

            When solid potassium halides are added to concentrated sulfuric acid, the following reactions take place: 

            reaction 1

            2KBr  +  2H2SO4  →  K2SO4  +  SO2  +  Br2  +  2H2O

            reaction 2

            8KI  +  5H2SO4  →  4K2SO4  +  H2S  +  4I 2  +  4H2O

            reaction 3

            2KCl  +  H2SO4  →  K2SO4  +  2HCl

            In each reaction, what is the largest change in the oxidation number of sulfur? 

             

            Reaction 1

            Reaction 2

            Reaction 3

            A

            B

            C

            D

            1

            2

            2

            4

            4

            4

            8

            8

            1

            0

            0

            1

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              91 mark

              What is formed at the electrodes during the electrolysis of molten potassium iodide? 

               

              Positive electrode

              Negative electrode

              A

              K+

              I-

              B

              K

              I2

              C

              I-

              K+

              D

              I2

              K

               

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                101 mark

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

                9-1-mcq-q10-ib-chemistry

                • 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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                11 mark

                When heated ammonium nitrate, NH4NO3, can decompose explosively.

                         NH4NO3 → N2O + 2H2

                The nitrogen atoms in NH4NO3 have different oxidation numbers. 

                What are the changes in oxidation numbers for each of the N atoms when this reaction proceeds?

                • +4, –4

                • –2, –4

                • +4, –6

                • +2, +6

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                21 mark

                In winemaking, to prevent the oxidation of ethanol by air, sulfur dioxide (SO2) is added. In order to calculate the amount of SO2, a sample is titrated with iodine (I2). The reaction is a one to one ratio for SO2 and I2 to produce H2SO4 as well as another product. 

                What is the change in the oxidation number of sulfur in this reaction?

                • +2 to +6

                • +4 to +6

                • +2 to +4

                • +4 to +5

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                31 mark

                20 cm3 of a 0.60 mol dm–3 solution of thallium nitrate (TlNO3) requires 40 cm3 of
                0.20 mol dm–3 acidified ammonium metavanadate (NH4VO3) to produce Tl3+(aq) ions. 

                Vanadium is the only element reduced in this reaction. What is the change in oxidation number of vanadium?

                • +1

                • +2

                • +3

                • +4

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                41 mark

                If a solution contains both bromine and chlorine, BrO3 ions are produced. 

                The reactions leading to the production of BrO3 ions are shown below: 

                Reaction 1:     Br2  +  H2O  →  HBr  +  HBrO 

                Reaction 2:     3HBrO  +  Cl2  →  2Cl   +  BrO3  +  Br2  +  3H+ 

                1

                Chlorine is reduced in reaction 2

                2

                Bromine is reduced in both reaction 1 and reaction 2

                3

                Bromine is oxidised in both reaction 1 and reaction 2

                Which statements about these reactions are correct?

                • 1 only 

                • 1 and 2 only

                • 2 and 3 only

                • 1, 2 and 3

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                51 mark

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

                                     2H+(aq)  +  2NO2(aq)  →  H2O(l)  +  NO(g)  +  NO2(g) 

                Which of the three statements below correctly describe 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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                61 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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                  71 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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                  81 mark

                  When molten magnesium chloride is electrolysed using graphite electrodes what are the products? 

                   

                  Product at cathode

                  (negative electrode)

                  Product at anode

                  ( positive electrode)

                  A

                  magnesium

                  chlorine

                  B

                  chlorine

                  magnesium

                  C

                  magnesium ions

                  chloride ions

                  D

                  chloride ions

                  magnesium ions

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                    91 mark

                    Use the information given about four reactions of metals to determine the order of reactivity from most reactive to least reactive

                       W(s) + X2+(aq) → W2+(aq) + X(s)

                       Y(s) + W2+(aq) → No Reaction

                       X(s) + Y2+(aq) → X2+(aq) + Y(s)

                       Z(s) + Y2+(aq) → No Reaction

                    • W > Y > X > Z

                    • X > W > Z > Y

                    • Z > Y > W > X

                    • W > X > Y > Z

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                    101 mark

                    Below are three statements about voltaic cells. 

                      1.    A redox reaction takes place which produces electrical energy
                      2.    At the cathode an oxidation reaction occurs
                      3.    Electrons move from the anode to the cathode 

                    The correct statements are

                    • I and II only  

                    • I and III only  

                    • II and III only 

                    • I, II and III

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