SUBDOMAIN 204.3
THE OXIDATION STATES OF MANGANESE
SCA4/5 Task Late Nite Lab
By
Nienke Adamse
12/3/10
ABSTRACT
In this experiment the various oxidation states that are formed by
the redox reaction of permanganate ion, MnO4  and the bisulfite
ion, HSO4  have been studied. The reducing agent that was used
was sodium bisulfate, NaHSO3 .
The redox reaction was studied inacidic, basic and neutral
 aqueous solutions.

In the acidic solution
the oxidation state of manganese was
+2,and the oxidation state of sulfur was +6, in neutral solution
the oxidation state of manganese was +3 and the oxidation state
of sulfur was +6, and in basic solution the oxidation state of
manganese was +6 and the oxidation state of sulfur was +6.
EXPERIMENT
Tools:
In this experiment the following tools and glassware were used:
3 pH meters
5 test tubes
Chemicals:
H2O
H2SO4



KMnO4
NaHSO3


NaOH
MnO2
Procedure:

1. Take 5 clean test tubes and place them on the workbench.
2. Add 5 mL of water to the first test tube. This is your color
standard against which the pale pink Mn+2 ion can be compared.
3. Add 5 mL of KMnO4 to the second test tube. This is your color
standard for the purple permanganate ion.
4. Add 2 mL of KMnO4 to test tubes 3, 4 and 5.
5. Add 1 mL of NaOH to test tube 3
6. Add 1 mL of H2SO4 to test tube 5.
7. Take 3 pH meters and place them into test tubes 3, 4 and 5.
Record the pH in the test tubes. You will see that test tube 3 is the
basic solution, test tube 4 is neutral, and test tube 5 is acidic.
8. Add five 1 mL increments of NaHSO3 to test tube 3. Observe
and record the results of the reaction, color and precipitation,
after each addition of 1 mL.
9. Add five 1 mL increments of NaHSO3 to test tube 4. Observe
and record the results of the reaction, color and precipitation,
after each addition of 1 mL.
10. Add five 1 mL increments of NaHSO3 to test tube 5. Observe
and record the results of the reaction, color and precipitation,
after each addition of 1 mL.
RESULTS
Table 1: color of solution and precipitation:
Color of:
1ml
2 ml
3 ml
4 ml
5 ml
#3
NaHSO3
green
NaHSO3
green
NaHSO3
green
NaHSO3
green
NaHSO3
green
solution
#3 
No 
No 
No 

No precip
No
precip.
precip.
precip.
precip.
#4
pink
pink
clear
clear
Clear
#4
No
brown
brown
brown
brown
precip.
precip.
#5
pink
pink
pink
pink
Very
precip.
solution
solution
light
pink
#5
no
no
no
no
no
precip
Table 2: pH values solution
pH

1ml
2 ml
3 ml
4 ml
5 ml
NaHSO3
NaHSO3
NaHSO3
NaHSO3
NaHSO3




#3
13.65
13.56
13.48
13.41
13.35
#4
7.00
7.38
7.41
7.38
7.35
#5
0.00
0.00
0.01
0.08
0.14
ANALYSIS
Test tube #3:
The reaction between NaHSO3 and KMnO4 (after adding 5 ml of
NaHSO3 ) in a basic solution (test tube #3) can be described with
the following equation:



2KMnO4  3NaHSO3  2NaOH  2H2O  NaOH  Na2 MnO4  NaHMnO4  K2SO4  NaHSO3  3H2O
The green solution indicates that the oxidation state of manganese

is +6, it shows the existence of the manganate ion, MnO42 in the
basic solution.
The oxidation state of sulfur in the NaHSO3 in this test tube is +4.

The sodium bisulfate functions here as a reducing agent and the

oxidation state of sulfur increases from +4 to +6. HSO3 is converted
to the sulfite ion SO32 .

Test tube #4:

The reaction between NaHSO3 and KMnO4 (after adding 5 ml of
NaHSO3 ) in a neutral solution (test tube #4) can be described with
the following equation:



KMnO4  NaHSO3  H2O  KMnO4  MnO2  K2SO4  Na2SO4  NaHSO3  H2O
The clear solution with the brown precipitation shows that the

oxidation state of manganese is +4, it shows that the manganese
dioxide, MnO2 has been formed in the reaction in the neutral
solution, this is a black solid. The reducing agent here is sodium
bi sulfate and the oxidation state of the sulfur increases from +4
to+6. It is being oxidized to the bisulfate ion HSO  .
3
Test tube #5:

The reaction between NaHSO3 and KMnO4 (after adding 5 ml of
NaHSO3 ) in a acid solution (test tube #5) can be described with
the following equation:



KMnO4  H2SO4  NaHSO3  H2O  H2SO4  MnSO4  K2SO4  Na2SO4  NaHSO4  H2O

The light pink solution in the test tube shows that the oxidation
state of manganese is +2, it shows that Mn 2 exists in the acidic
solution. The manganate ion MnO42 has been reduced to Mn 2 .
Sodium bisulfite is the reducing agent in this redox reaction. The

oxidation state of sulfur increases to +6. In this acidic solution


sodium bisulfite is converted into sulfurous acid H2SO3 and is
oxidized into the bisulfate ion HSO4 .


CONCLUSION AND DISCUSSION
Oxidation is the process where a molecule, atom or ion increases
its oxidation state.
Reduction is the process where a molecule, atom or ion decreases
its oxidation state.
In a redox reaction (an oxidation-reduction reaction) , the atoms
change their oxidation number (oxidation state).
An oxidizing agent is the oxidant that gains electrons and is
reduced.
The reducing agent is the reductant that loses electrons and is
oxidized.
Substances, such as the permanganate ion, that have the ability
to oxidize other substances are oxidizers or oxidizing agents. The
oxidizing agent is also called the electron acceptor because it
accepts or removes electrons from other substances and is thus
itself reduced.
Substances, such as sodium bisulfite, that have the ability to
reduce other substances are reducing or reducing agents. The
reducing agent is also called an electron donor because it
transfers electrons to another substance, thus becoming oxidized
itself.
The oxidation states ( or oxidation numbers) concept of the redox
reactions is a way to keep track of the electrons. (Zumdahl, 2009)
defines the oxidations states of the atoms in a covalent bond as: “
the imaginary charges the atoms would have shared if the shared
electrons were divided equally between identical atoms bonded to
each other or, for different atoms, were all assigned to the atom in
each bond that has the greater attraction for electrons.”
In test tube # 5, the +2 oxidation state of Mn results from removal
of the two 4s electrons, leaving a "high spin" ion in which all
five of the 3d orbitals contain a single electron. The pale pink
color of the solution is the result of the absorption of almost all
visible light by this ion
In test tube #3, manganese exists in the +6 oxidation state as the
manganate ion, MnO42 , this ion is green in color and is only
stable in basic solution,.
In test tube #4, the manganese ion exists in the +4 oxidation

state as manganese dioxide, MnO2 . This a solid that is fairly
stable, Mn 4 does not exist in aqueous solutions.
The reducing agent inthis reaction was sodium bisulfite: NaHSO3 .

The oxidation state for sulfur in sodium bisulfite is +4 and
increases to +6. In neutral solutions the bisulfate ion HSO3 exists
 SO 2 . In an
and in basic solutions it is oxidized to the sulfate ion
4
acidic solution it is oxidized to sulfuric acid, H2SO3 .



REFERENCES
Late Nite labs: Laboratory Simulations for Science Education.
(2006)- Oxidation States of Manganese.
http://www.latenitelabs.com/
Zumdahl, S.S and Zumdahl, S.A (2009) Chemistry. Seventh
Edition
Boston, MA: Houghton Mifflin Company