Lesson 9: Wrap Up

 

There are a great many important day to day redox reactions that have not been discussed in this lesson. However, from what you have learned, you should be able to start recognizing many of them as you come across them and start learning more about them.

Biological Redox Reactions

Many redox reactions occur in biological systems. For example, food is oxidized to provide energy. Many biological reactions involved in energy production are electron transfer (redox) reactions. Also, plants reduce CO₂ and H₂O to make glucose and other carbohydrates. Oxygen, oddly enough, is oxidized in th photosynthetic process.

Corrosion and Oxidation

Corrosion and oxidation includes such things as rusting of iron and certain types of spoiling of food, such as fats going rancid. These reactions are very natural, but they are generally considered undesirable. Consequently, processes have been developed to stop, slow or divert these electron flow reactions. Those processes include both sacrificial and protective methods.

You may have heard about antioxidants and anodic protection. These are sacrificial methods. The antioxidant or the anode is sacrificed by letting it be oxidized instead of the thing we don't want to be oxidized.

On the other hand, the use of films, coatings and platings are protective methods. These materials are highly resistant to oxidation and are used to cover the thing we don't want to be oxidized so that the oxidizing agent cannot make contact with it.

Have you thought about why we worry about oxidation more than reduction? It is really very simple. We live in an oxidizing atmosphere, made so by the vast presence of oxygen in it.

 

Conclusion

I believe that takes care of everything that we need to cover in this lesson on oxidation-reduction reactions. Again, you should be sure to go back and review the objectives and be able to do everything that is listed there. Take the self quiz and check your answers. Be sure to complete and turn in your problem set. Also, I suggest that you read the text and answer the questions at the end of the chapter, as indicated on the objective sheet. Your laboratory report for this particular experiment need not be a formal report. Instead, turn in the work sheets on the experiment that you did, answering the questions and filling in the blanks and that type of thing. However, do be sure to include the purpose of the experiment at the top of the first page. Also, when you answer questions about which chemicals are reacting, be sure to distinguish between the metallic and ionic forms (or the reduced and oxidized forms) of the chemicals you worked with.

 

If you enjoyed the reactions in lab of the metals with the metal ions, here is a link to some simulations with more combinations.

 

Self Quiz Answers

1. Which of the following chemicals can be oxidized most easily?

*a. Na
b. Mg
c. Cl₂
d. F^-
e. Al³⁺

 

2. Which of the following is/are oxidation-reduction reactions?

a. Mg + 2H⁺ Mg²⁺ + H₂
b. N₂ + O₂ 2NO
c. NaCl + AgNO₃ AgCl + NaNO₃
*d. (a) and (b)
e. (a), (b) and (c)

 

3. Oxidation and reduction must take place at the same time because electrons are:

a. gained.
b. lost.
*c. transferred.

 

4. What voltage could a cell generate (under ideal conditions) using the following reaction?

3 Mg + 2 AlCl₃ 3 MgCl₂ + 2 Al

a. -4.03 v
b. -0.71 v
*c. +0.71 v
d. +3.79 v
e. +4.03 v

 

5. Electrolytic cells:

1. can be used to force reactions that do not occur spontaneously.
2. need an external source of electricity.
3. can be used for electroplating.

a. only one of these
b. 1 and 2
c. 1 and 3
d. 2 and 3
*e. all of these

 

6. Which of the following combinations will react in a spontaneous oxidation-reduction reaction?

a. Zn + Zn²⁺
b. Cr + Fe
*c. Cd + Ni²⁺
d. Sn + Fe²⁺
e. Ag⁺ + Br₂

 

7. The gain of electrons is called:

a. oxidation.
b. oxidation-reduction.
c. redox.
*d. reduction.
e. none of the above.

 

8. If two copper electrodes are put into a silver nitrate solution and a current is run through the cell, what will happen at the anode?

a. Copper will plate out.
b. Silver will plate out.
*c. Copper will go into solution.
d. Silver will go into solution.

 

9. In what kind of cell would this reaction occur?

2 Al + 3 CuCl₂ 2 AlCl₃ + 3 Cu

a. anodic
b. cathodic
c. electrolytic
d. hypnotic
*e. voltaic

 

10. Diagram a voltaic cell using this reaction:  Ni + Pb²⁺ Pb + Ni²⁺.

Indicate the placement of the chemicals, the location of the electron flow, and the half reaction occurring at each electrode.

 

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