0%

DP IB Chemistry: SL

Topic Questions

Home / IB / Chemistry: SL / DP / Topic Questions / 9. Redox Processes / 9.1 Redox Processes / Structured Questions: Paper 2


9.1 Redox Processes

Question 1a

Marks: 3
a)
A student sets up a titration to determine the amount of iron(II) sulfate in an iron tablet. They titrate the iron(II) sulfate solution with potassium manganate(VII) solution.

i)
Write the balanced, ionic half equations to show the reduction of the manganate(VII) ion and the oxidation of the Fe2+.
[2]

ii)
Use your answers to part (i) to write an overall redox equation for the titration of iron(II) sulfate with potassium manganate(VII) solution.
[1]
    Assess your score
      

    Question 1b

    Marks: 2
    b)
    The iron(II) sulfate solution is acidified before titration to stop the manganate ion forming unwanted manganese dioxide. 

    Explain the effect that not acidifying the iron(II) sulfate would have on the final 
    calculation of the estimated mass of iron.
     [2]
      Assess your score
        

      Question 1c

      Marks: 5
      c)
      The student dissolved the iron tablet in excess sulfuric acid and made the solution up to 250 cm3 in a volumetric flask. 25.0 cm3 of this solution was titrated with 0.0100 mol dm-3 potassium manganate(VII) solution. The average titre was found to be 26.65 cm3 of potassium manganate(VII) solution. 

      i)
      Calculate the amount, in moles, of iron(II) ions in the 250 cm3 solution.
      [3]
      ii)
      Calculate the mass of iron, in mg, in the tablet. 
      [2]
        Assess your score
          
        Key Concepts
        Redox Titrations

        Question 1d

        Marks: 1
        d)
        Iron sulfate reacts with chromium to produce chromium(III) sulfate, Cr2(SO4)3 , and iron

        Deduce the overall ionic equation for the reaction occurring 
        [1]

          Assess your score
            

          Question 2a

          Marks: 5
          a)
          Molten potassium bromide can be electrolysed using graphite electrodes.

          i)
          Draw the essential components of this electrolytic cell.
          [3]
          ii)
          Identify the products at each electrode.
          [2]

            Assess your score
              
            Key Concepts
            Electrolytic cells

            Question 2b

            Marks: 3
            b)
            State the half equations for the oxidation and reduction processes and deduce the overall cell reaction, including state symbols. 

            Oxidation half equation …………………

            Reduction half equation ……………….

            Overall equation ……………………………
            [3]

              Assess your score
                

              Question 2c

              Marks: 1
              c)
              Explain why solid potassium bromide does not conduct electricity. 
              [1]

                Assess your score
                  
                Key Concepts
                Electrolytic cells

                Question 2d

                Marks: 3
                d)
                A voltaic cell is made from a half-cell containing a magnesium electrode in a solution of magnesium nitrate and a half-cell containing a silver electrode in a solution of silver(I) nitrate.

                9-1-ib-sl-sq-hard-q2d-mg-and-ag-voltaic-cell
                i)
                Use section 25 of the data booklet to determine which electrode is positive and to write the equation for the reaction at the positive electrode, including state symbols. 
                [1]
                ii)
                Compare the processes at the positive electrodes in voltaic and electrolytic cells. 
                [2]

                  Assess your score
                    

                  Question 3a

                  Marks: 3
                  a)
                  State the oxidation state of phosphorus in the following compounds.

                  H2PO4………………………………………………………..

                  HPO………………………………………………………..

                  H3PO………………………………………………………..
                  [3]
                    Assess your score
                      

                    Question 3b

                    Marks: 2
                    b)
                    The tetrathionate ion is shown below:
                    1-20

                    i)

                    Determine the oxidation state of sulfur in the ion.
                    [1]

                     

                    ii)
                    Justify your answer to part ii).
                    [1]
                      Assess your score
                        

                      Question 3c

                      Marks: 3
                      c)
                      Sodium tetrathionate can be formed by reacting sodium thiosulfate, Na2S2O3, with iodine.

                      i)
                      State the balanced symbol equation for this reaction.
                      [2]
                      ii)
                      Identify the oxidising agent in this reaction.
                      [1]
                        Assess your score
                          

                        Question 3d

                        Marks: 1
                        d)
                        Describe the expected observation to show that this reaction had gone to completion.
                        [1]
                          Assess your score
                            
                          Key Concepts
                          Redox Titrations

                          Question 4a

                          Marks: 3
                          a)
                          A 150.0 cm3 sample of pond water was analysed using the Winkler method to determine its biological oxygen demand (BOD). Initially it took 29.40 cm3 of 0.010 mol dm-3 Na2S2O3 to react with iodine.

                          After five days it required 13.70 cmof 0.010 mol dm-3 Na2S2O3 to react with iodine.

                          The unbalanced equations for the Winker method are shown below.

                          ......Mn2+ (aq) + ......OH- (aq) + O2 (aq) → ......MnO2 (s) + ......H2O (l) 

                          MnO2 (s) + ......I(aq) + ......H(aq) → Mn2+ (aq) + I2 (aq) + ......H2O (l) 

                          ......S2O32- (aq) + I2 (aq) → S4O62- + ......I- (aq)  

                          Balance the equations for the Winkler method. 
                          [3]
                            Assess your score
                              

                            Question 4b

                            Marks: 3
                            b)
                            Deduce the reducing agent in the reaction between S2O32- and I2. Justify your answer. 

                              Assess your score
                                

                              Question 4c

                              Marks: 3
                              c)
                              Use the information in part a) and section 6 in your data booklet to determine the initial concentration, in ppm, of oxygen. 
                                Assess your score
                                  

                                Question 4d

                                Marks: 3
                                d)
                                Use the information in part a) and section 6 in the data booklet to determine the concentration, in g dm-3, of oxygen after five days. 
                                [3]
                                  Assess your score
                                    

                                  Question 4e

                                  Marks: 2
                                  e)
                                  Determine the BOD of the pond water in ppm. 
                                  [2]

                                    Assess your score
                                      

                                    Question 5a

                                    Marks: 3
                                    a)
                                    15.00 cm3 of ethanedioic acid, H2C2O4 (aq), requires 10.30 cm3 of a 0.250 mol dm-3 solution of sodium hydroxide, NaOH (aq), for complete neutralisation using a phenolphthalein indicator for the first permanent colour change.

                                    15.00 cm3 of the same H2C2O4 solution required 12.35 cm3 of potassium permanganate solution, KMnO4 (aq), solution for complete oxidation to carbon dioxide and water in the presence of dilute sulfuric acid to further acidify the H2C2O4 solution for the first permanent colour change. 

                                    i)
                                    Using the following equation, calculate the amount, in moles, of H2C2O4 (aq).

                                    H2C2O4 (aq) + 2NaOH (aq) → Na2C2O4 (aq)+ 2H2O (l) 

                                    [2]

                                    ii)
                                    Calculate the concentration, in mol dm-3, of H2C2O4 (aq). 
                                    [1]
                                      Assess your score
                                        

                                      Question 5b

                                      Marks: 3
                                      b)
                                      Deduce the following half equations and overall redox equation for the reaction outlined in part a).

                                      MnO4- (aq) to Mn2+ (aq) .........................

                                      H2C2O4 (aq) to CO2 (g) ...........................

                                      Overall equation ......................................

                                      [3]

                                        Assess your score
                                          
                                        Key Concepts
                                        Redox Titrations

                                        Question 5c

                                        Marks: 2
                                        c)
                                        Calculate the concentration, in mol dm-3of the potassium manganate(VII), KMnO4, solution.
                                          Assess your score