Metal Activity and Potential Lab
The activity or electromotive series of metals is a listing of the metals in decreasing order
of their reactivity with hydrogen-ion sources such as water and acids. In the reaction with
a hydrogen-ion source, the metal is oxidized to a metal ion, and the hydrogen ion is
reduced to H2. The ordering of the activity series can be related to the standard reduction
potential of a metal cation.
The more positive the standard reduction potential of the cation, the more difficult it is to
oxidize the metal to a hydrated metal cation and the later that metal falls in the series.
Although this correlation cannot give precise ordering of elements of very similar
electronegativities (Pauling electronegativity values have uncertainties of +/- 0.05 units),
elements can be placed into activity groups based on Pauling electronegativities.
1. Very Electropositive Metals
Most active metals have low electronegativities (EN < 1.4). These cations
generally have reduction potentials of -1.6 V or below.
Group Reactivity Features
o
o
o
o
react with water to release hydrogen
goods reducing agents
not very good oxidizing agents
ions can't be reduced to the metal in aqueous
solution
2. Electropositive Metals
Metals in this group have electronegativities that fall between 1.4 and 1.9. Cations
of these metals generally have standard reduction potentials between 0.0 and -1.6
V.
Group Reactivity Features
o
o
do not react very readily with water to release
hydrogen
react with H+
3. Electronegative Metals
Metals in this group have electronegativities between 1.9 and 2.54. Cations of
these metals generally have positive standard reduction potentials.
Group Reactivity Features
o
o
o
o
Metals are not oxidized by H+
These are good oxidizing agents
Oxidize H2 producingH+ and depositing the metal
from an aqueous solution
Cations of these less active metals will oxidize more
active metals to a cation. The less active metal is deposited
as the metal.
Other Oxidizing Agents
The activity groups also apply to oxidizing agents such as O2 or oxidizing oxo acids.
1. Very Electropositive
Metals in this group readily ignite in air (burn) forming the oxides. Fires which
result can't be extinguished with water (produces flammable H), CCl4 (an
oxidizing agent) or CO2. These fires are best extinguished with sand which
smothers the flames and does not react.
2. Electropositive
These metals do not burn as readily in air. The surfaces of these metals will
tarnish in the presence of oxygen forming a protective oxide coating. This coating
protects the bulk of the metal against further oxidation (the metal is passivated).
If the surface of the metal is in contact with both oxygen and water, corrosion can
occur. In corrosion, the metal acts as an anode and is oxidized.
Fe (s)
Fe2+ + 2e-
Some other point on the surface acts as a cathode where oxygen is reduced to OH. Hydroxide or other ions migrate back to the Fe2+ completing the electrochemical
circuit. The ferrous ions precipitate as Fe(OH)2 which further oxidizes and
dehydrates to form rust. Corrosion occurs at pH and pE's within the predominance
area of Fe2+. Corrosion doesn't occur well in basic solutions due to the coating
FeO or Fe(OH)2.
3. Electronegative Metals
Since many metals in this group are not corroded by oxygen, they are called
"nobel metals" and are used in coinage and jewelry. Some in this group are slowly
oxidized. The oxides formed are not very stable and can be decomposed by
heating.
Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
Place into a clean Petri dish 10 drops of a 1.0 M Pb 2+ solution.
Place into another Petri dish 10 drops of a 1.0 M Cu2+ solution.
Add 9 mls of a 1M Acetic acid solution to each dish
Add 10 mls of Silica Solution to each dish
Wait for gel solution to set.
Clean with sand paper the following metals: Ni, Fe, Pb, Al, Sn, Cu, Mg
Place each of the metals into the Gel.
Wait 15 minutes and record any change to the surface of the metals
immersed into the gel.
Note: The gels contain the metal ions and Hydrogen ions placed in step 1-3.
Data: Draw pictures of gel before and after the metals were placed into them.
Conclusion:
Determine the Red ox reactions taking place in each of the gels.
Explain any gas formation or coloration changes that take place in the gels.
Explain why or why not the metals did or did not react with the ions in the gel