44 Oxidation-Reduction Reactions

Background

 The rusting of iron and the combustion of gasoline are common examples of oxidation-reduction reactions. Oxidation reactions are also thought to be partly responsible for the aging of the human body. Every oxidation reaction involves a transfer of electrons from the substance oxidized to the substance reduced. A substance undergoing oxidation gives up, or loses, electrons; a substance undergoing reduction gains electrons. The ease with which a substance oxidizes depends on the substance. For instance, iron oxidizes more easily than either silver or gold.

In this experiment you will study some oxidation-reduction reactions that occur between metals and metals ions. On the basis of your experiments, you will organize these substances into a series according to their relative ease of oxidation.

Goals

· Observe several oxidation-reduction reactions.
· Classify the substances tested in terms of ease of oxidation.

Equipment

safety goggles 1 plastic wash bottle
9 small test tubes 1 10-mL graduated cylinder
1 test tube rack

Materials

3 strips of copper (Cu), each 0.1 M lead (II),nitrate
0.25 m x 0.50 cm x 2.00 cm Pb (No3)2

3 strips of lead (Pb), each 0.1 M zinc nitrate, Zn (No3)2
0.25 mm x 0.50 cm x 2.00 cm steel wool

3 strips of zinc (Zn), each 8 glass-marking pencils
0.25 mm x 0.50 cm x 2.00 cm distilled water

0.1 M copper (II) nitrate,
Cu (NO3)2

Safety

· Note the Safety Symbols used here and in the Procedure section. Review safety information on pages 7-10.
· Always wear safety goggles when working in the lab.
· Copper and lead compounds are toxic.

Procedure

Copy Table 44.1 into your laboratory notebook. As you perform the experiment, record your observations in this table.

1. Polish the small metal strips of copper, lead, and zinc with steel wool.

2. CAUTION: Copper(II) nitrate is toxic. Label three test tubes 0.1 M Cu(NO3)2. Add 3 mL of 0.1 M copper (II) nitrate to each test tube. In one tube place a strip of copper. In another place a strip of lead. In the third place a strip of zinc. Put the tubes in a test-tube rack.

3. CAUTION: Lead nitrate is toxic. Repeat step 2, labeling the tubes 0.1 M Pb(NO3)2 and using 0.1 M lead (II) nitrate in place of copper (II) nitrate.

4. Repeat step 2, labeling the tubes 0.1 M Zn (NO3)2 and using 0.1 M zinc nitrated in place of copper (II) nitrate.

5. Allow the test tubes to stand undisturbed for 5-10 minutes. Record your observations in Table 44.1, briefly describing evidence of any reaction.

6. Return the metal strips for reuse and dispose of the solutions as instructed by your teacher.

Data Record
 

Table 44.1 Part A.

Reactions of 

Metals and

Metal Ions

Cu2+

Pb2+

Zn2+

Cu (s)

Pb (s)

Zn (s)

Conclusions
 
1. Write balanced equations for any reactions that you have observed between solid metals and metal ions.

2. Which metal was oxidized by both of the other two metals?

3. Which metal was oxidized by only one of the other two metals?

4. Which metal was oxidized by neither of the other metals

5. Write balanced half-reactions for the reduction of each of the three metal ions used in this experiment. Write the equations so that the metal ions are shown as reactants and the solid metals are shown as products. List these half-reactions so that the most easily oxidized metal is given last.

Extension
 
1. The relative ease of oxidation of the halogens is in this order: chlorine, bromine, iodine, with iodine the most easily oxidized. Design an experiment that would allow you to determine if the halogens are less or more easily oxidized that the metals used in this experiment.