Oxidation Reduction Reactions Worksheet - Answer Key

 

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  1. What is an oxidation-reduction (or redox) reaction?

    This is a reaction in which electrons are transferred between reactants. 

    2.  

     

  2. What do the following terms mean?

      3.  

    • Oxidation

      Oxidation is a loss of electrons

      •  

    • Reduction

      Reduction is a gain of electrons

      •  

    • What is a helpful way to remember this?
                             
      A mnemonic device  to help you remember:

      OIL RIG  (Oxidation Is Loss Reduction Is Gain)

     

     

  3. What is an oxidation number?

    An oxidation number allows one to keep track of electron flow in a reaction.

    4.  

     

  4. Assign the oxidation number for the following
    • KMnO4

       Oxidation Numbers
      K:        +1
      Mn:    +7
      O:        –2 (for each oxygen)
    • (NH4)2HPO4

      Oxidation Numbers
      N:        –3
      H:        +1 (for each hydrogen)
      P:        +5
      O:        –2 (for each oxygen)
    • Fe3O4

      Oxidation Numbers
      Fe:      +8/3
      O:        –2 (for each oxygen)
    • XeOF4

      Oxidation Numbers
      Xe:      +6
      O:        –2
      F:         –1 (for each fluorine)

     

     

  5. What are the practical applications of oxidation numbers?

    They allow us to determine what has been oxidized and what has been reduced.

    6.  

     

  6. Consider:

    CH4 (g)     + 2O2 (g) → CO2 (g) + 2H2O (g)

    Determine what was oxidized and what was reduced.

    C:  -4     → +4           Carbon became less negative (lost electrons, oxidized)
    H: +1     → +1              Hydrogen didn’t undergo change (unimportant)
    O: 0     → -2                 Oxygen gained negativity (gained electrons, reduced)

    7.  

     

  7. What is an
    • Oxidizing agent?

      The oxidizing agent is the reactant that contains the species that gets reduced.
    • Reducing agent?

      The reducing agent is the reactant that contains the species that gets oxidized.

     

  8. Consider:



    Cu: +1     → +2        Lost electrons → oxidized
    Cl: -1     → -1           Nothing
    Cu: +1     → 0           Gained electrons → reduced

    determine the following:

      9.  

    • What was oxidized?

      Copper
    • What was reduced?

      Copper
    • What was the reducing agent?

      CuCl
    • What was the oxidizing agent?

      CuCl

     

     

  9. Consider:




    Zn:  0     → +2         Lost electrons → oxidized
    H: +1     →  0           Gained electrons→ reduced
    Cl: -1     → -1           Nothing
    • What was oxidized?

      Zinc
    • What was reduced?

      Hydrogen
    • What was the reducing agent?

      Zn
    • What was the oxidizing agent?

      HCl

     

     

  10. What are the steps to balancing a redox reaction using the ½ reaction method?

    1.  Break the reaction up into two half reactions.  One for is the
    reduction and the other is the reduction.

    2.  Balance all elements in the reaction except for oxygen and hydrogen.

    3.  Balance the oxygen by adding H2O.

    4.  Balance the hydrogen by adding H+.

    5.  Balance charge by adding electrons.

    6.  Equalize the number of electrons coming out of one reaction with
    those going into the other.

    7.  Add up the two reactions.  Make sure to cancel out where necessary.
    .                                                                                                                                .

    If you asked to balance under acidic conditions – you can stop after this step.  If you are asked to balance under basic conditions, you will need to proceed onto step 8.
    .                                                                                                                                .

    8.  Neutralize the H+ by adding in the same number of moles of  –OH.  Make sure to add the –OH to both sides of the reaction.

    11.  

     

  11. Balance the following redox reaction using the ½ reaction method just described  under both acidic and basic conditions.

    MnO4 (aq) + H2C­2O4 (aq)­     → Mn2+(aq) + CO2 (g)

    Acidic Conditions:
    6 H+ + 2MnO4- + 5 H2C2O4    → 2 Mn2+ + 8 H2O + 10 CO2

    Basic Conditions:
    2MnO4- + 5 H2C2O4    → 2 Mn2+ + 2 H2O + 10 CO2 + 6 -OH

    12.  

     

  12. A 45.20 mL sample of sol’n containing Fe2+ ions is titrated with a 0.225M KMnO4 sol’n.  It required 23.51 mL of KMnO4 sol’n to oxidize all the Fe2+ ions to Fe3+ by the following reaction

    MnO4- (aq) + Fe2+(aq)     → Mn2+(aq) + Fe3+(aq)   

    What was the concentration of Fe2+ in the sol’n?

    0.0585 M Fe2+

    13.  

     

  13. Consider:

    Na2SO4 (aq) + Pb(NO3)2 (aq)    →

      14.  

    • What are the three types of reaction equations that can be used to describe this reaction?
      •  
      •  

    • What products, if any, form? How could you tell if no product was formed?

     

     

  14. Consider the reaction between silver nitrate and calcium chloride
    1. How many grams of silver chloride can be prepared by the reaction of 100.0 mL of 0.20M silver nitrate with 100.0 mL of 0.15 M calcium chloride?
    2. Calculate the concentration, in M, for each of the ions remaining in sol’n after reaction has gone to completion.

    15.  

     

  15. What volume of 0.900M Na3PO4 is required to precipitate all the lead (II) ions from 160.0 mL of 0.650M Pb(NO3)2?

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