Mr Cole Chemistry

Variable Oxidation State Questions

  • Questions
  • Answers
  1. State the oxidation number on the following complexes.
    1. [Cu(H2O)6]2+
    2. [Ag(NH3)2]+
    3. Pt(NH3)2Cl2
    4. [Fe(H2O)4(OH)2]+
    5. [Al(OH)4]–
    6. [Fe(CN)6]3-
    7. [Co(C2O4)3]4-
    8. [Cr(H2O)5SO4]+
  2. Which of the following combinations will react? For those that do react, write the equation for the reaction.
    1. Lead and Lead (IV) ions.
    2. MnO2 and Fe2+
    3. MnO2 and Pb4+
    4. Co2+ and Cu+
    5. Cobalt and tetraamminecopper complex
    6. Hexacyanoferrate (III) and Mn2+
  3.  State the changes you can make to a transition metal ion that can change the ease at which it is oxidised or reduced.
  4. For the following substances, choose another species that will successfully cause the reaction to occur.
    1. Co –> Co2+
    2. Fe3+ –> Fe
    3. Cr2O72- –> Cr2+
    4. Mn –> Mn2+
    5. VO3– –> V3+
  5. Analyse the following pairs using the electrode potentials data sheet provided.
    1. Out of MnO4– and H2O2, which is the better oxidising agent?
    2. Out of Sn4+ and Ag, which is the better oxidising agent?
    3. Out of Co2+ and Cu, which is the better reducing agent?
    4. Out of Fe2+ and Sn2+, which is the better reducing agent?
  1. State the oxidation number on the following complexes.
    1. [Cu(H2O)6]2+
      +2
    2. [Ag(NH3)2]+
      +1
    3. Pt(NH3)2Cl2
      +2
    4. [Fe(H2O)4(OH)2]+
      +3
    5. [Al(OH)4]–
      +3
    6. [Fe(CN)6]3-
      +3
    7. [Co(C2O4)3]4-
      +2
    8. [Cr(H2O)5SO4]+
      +3
  2. Which of the following combinations will react? For those that do react, write the equation for the reaction.
    1. Lead and Lead (IV) ions.
      Yes
      Pb + Pb4+ –> 2Pb2+
    2. MnO2 and Fe2+
      Yes
      MnO2 + 4H+ + 2Fe2+ –> Mn2+ + 2H2O + 2Fe3+  
    3. MnO2 and Pb4+
      Yes
      MnO2 + 2H2O –> MnO4– + 4H+ + 3e–
      Pb4+ + 2e– –> Pb2+
      2MnO2 + 4H2O + 3Pb4+ –> 2MnO4– + 8H+ + 3Pb2+
    4. Co2+ and Cu+
      No
    5. Cobalt and tetraamminecopper complex
      Yes
      [Cu(NH3)4]2+ + 2e– –> Cu + 4NH3
      Co –> Co2+ + 2e–
      [Cu(NH3)4]2+ + Co –> Cu + 4NH3 + Co2+
      OR
      [Cu(NH3)4]2+ + Co –> Cu + [Co(NH3)4]2+
    6. Hexacyanoferrate (III) and Mn2+
      No
  3.  State the changes you can make to a transition metal ion that can change the ease at which it is oxidised or reduced.
    Oxidation State, ligand, coordination number, pH
  4. For the following substances, choose another species that will successfully cause the reaction to occur.
    1. Co –> Co2+
      Anything with an Eo higher than -0.28 but lower than 1.82 and is an oxidising agent (must be on the left side of the table), such as Br2.
    2. Fe3+ –> Fe
      Anything with an Eo lower than -0.44 and is a reducing agent (must be on the right side of the table), such as Ca.
    3. Cr2O72- –> Cr2+
      Anything with an Eo -0.41 but higher than -0.91 and is a reducing agent (must be on the right side of the table), such as Zn.
    4. Mn –> Mn2+
      Anything with an Eo higher than -1.18 but lower than 1.23 and is an oxidising agent (must be on the left side of the table), such as Fe3+
    5. VO3– –> V3+
      Anything with an Eo lower than 0.34 but higher than -0.26, and is a reducing agent (must be on the right side of the table), such as Sn2+
  5. Analyse the following pairs using the electrode potentials data sheet provided here.
    1. Out of MnO4– and H2O2, which is the better oxidising agent?
      MnO4– has an Eo of +1.67 and SO42- has an Eo of +0.17. MnO4– is a better oxidising agent.
    2. Out of Sn4+ and Ag, which is the better oxidising agent?
      Sn4+ has an Eo of +0.15 and Ag has an Eo of +0.8. However, Ag is not an oxidising agent, it is a reducing agent. Sn4+ is the better oxidising agent.
    3. Out of Co2+ and Cu, which is the better reducing agent?
      Co2+ has an Eo of -0.128 but that is it behaving as an oxidising agent. It has an Eo value of +1.82 when it acts as a reducing agent. Cu has an Eo of +0.34. Cu is the better reducing agent.
    4. Out of Fe2+ and Sn2+, which is the better reducing agent?
      Fe2+ has an Eo of -0.44 but that is it behaving as an oxidising agent. It has an Eo value of +0.77 when it is behaving as a reducing agent. Sn2+ has an Eo value of +0.15 when it is behaving as a reducing agent. Fe2+ is the better reducing agent.
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