MICROCHEM
KIT SAMPLE EXPERIMENT:
MicroChem Kit Experiment #6
6. SINGLE REPLACEMENT REACTIONS: OXIDATION-REDUCTION
GOALS
1. To become familiar with single replacement reactions.
2. To gain a better understanding of oxidation, reduction and oxidation-reduction
reactions.
3. To better understand the reactivities of some metals.
BACKGROUND
Single replacement reactions are a common type of chemical reaction.
In the case of metals, a more reactive metal will replace a less
reactive metal. For example, elemental nickel will oxidize and force
copper ions to reduce to form elemental copper. One equation for
this is:
Ni(s) + Cu(NO3)2(aq) > Cu(s) + Ni(NO3)2(aq)(1)
Consider only the nickel and the copper:
&Ni(s) + Cu2+(aq) > Cu(s) + Ni2+(aq) (2)
Nickel is more reactive than copper and replaces the copper in this
reaction. Since only one element replaces another this is a single
replacement reaction.
Consider only the elemental nickel and the nickel cations:
Ni > Ni2+ + 2e- (3)
The nickel atoms each lose two electrons and are now cations with
a charge of 2+. Nickel is oxidized since its oxidation number has
increased. Ionic copper is the oxidizing agent since it takes part
in the oxidation of nickel. Note that oxygen does not take part
in this oxidation reaction.
Now consider only the copper cations and the elemental copper:
Cu2+ + 2e- > Cu (4)
The copper cations gain two electrons and are now elemental copper
with a charge of zero. Copper is reduced in this reaction since
its oxidation state is reduced from 2+ to zero. Nickel is the reducing
agent since it takes part in the reduction of ionic copper.
In this reaction NO3- is unchanged. It is
a spectator ion.
| Materials |
Equipment |
Reagents:
0.1M copper nitrate, Cu(NO3)2
0.1M lead nitrate, Pb(NO3)2
0.1M zinc nitrate, Zn(NO3)2
Copper metal
Lead metal
Zinc metal |
96 well reaction plate
Cotton swabs
Plastic toothpick |
PROCEDURE
1. Put a small piece of copper in each well from A1 through A3,
a small piece of lead in each well from B1 through B3, and a small
piece of zinc in each well from C1 through C3.
2. Put five drops of Cu(NO3)2 in wells A1
through C1 (the first column), five drops of Pb(NO3)2
in wells A2 through C2, and five drops of Zn(NO3)2
in wells A3 through C3. The pieces of metal may tend to "float"
on the surface tension of the solution and need to be pushed down
with a plastic toothpick.
3. It will take a few minutes for the reactions to take place.
4. Record which wells have a reaction in Table 1.
5. Record the metals that were oxidized and the respective oxidizing
agents in Table 2.
RESULTS, Single Replacement Reactions
Table 1
| Metals/Solutions
| Cu(NO3)2
| Pb(NO3)2
| Zn(NO3)2
|
| Cu
|
|
| |
| Pb
|
|
| |
| Zn
|
|
| |
Table 2
| Metals
| Was the metal oxidized?
| Oxidizing agent(s)
|
| Cu
|
| |
| Pb
|
| |
| Zn
|
| |
1. Which metal is the most reactive? How do you know this?
2. Rank the metals in order of increasing reactivity.
3. Give the chemical equations for each single replacement reaction
that took place.
4. Was Pb2+ reduced? If so, what metal(s) acted as a
reducing agent?
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