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, and the bisulfite ion, have been studied. The reducing agent that was used was sodium bisulfate, .
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:
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 solution / green / green / green / green / green
#3 precip. / No precip. / No precip. / No precip. / No precip / No precip.
#4 solution / pink / pink / clear / clear / Clear
#4 precip. / No precip. / brown / brown / brown / brown
#5 solution / pink / pink / pink / pink / Very light pink
#5 precip / no / no / no / no / no
Table 2: pH values solution
pH / 1ml / 2 ml / 3 ml / 4 ml / 5 ml#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 and (after adding 5 ml of ) in a basic solution (test tube #3) can be described with the following equation:
The green solution indicates that the oxidation state of manganese is +6, it shows the existence of the manganate ion, in the basic solution.
The oxidation state of sulfur in the in this test tubeis +4. The sodium bisulfate functions here as a reducing agent and the oxidation state of sulfur increases from +4 to +6. is converted to the sulfite ion .
Test tube #4:
The reaction between and (after adding 5 ml of ) in a neutral solution (test tube #4) can be described with the following equation:
The clear solution with the brown precipitation shows that the oxidation state of manganese is +4, it shows that the manganese dioxide, 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 .
Test tube #5:
The reaction between and (after adding 5 ml of ) in a acid solution (test tube #5) can be described with the following equation:
The light pink solution in the test tube shows that the oxidation state of manganese is +2, it shows that exists in the acidic solution. The manganate ion has been reduced to .
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 and is oxidized into the bisulfate ion .
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 agentis 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, , 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, . This a solid that is fairly stable, does not exist in aqueous solutions.
The reducing agent in this reaction was sodium bisulfite: . The oxidation state for sulfur in sodium bisulfite is +4 and increases to +6. In neutral solutions the bisulfate ion exists and in basic solutions it is oxidized to the sulfate ion . In an acidic solution it is oxidized to sulfuric acid, .
REFERENCES
Late Nite labs: Laboratory Simulations for Science Education. (2006)- Oxidation States of Manganese.
Zumdahl, S.S and Zumdahl, S.A (2009) Chemistry. Seventh Edition
Boston, MA: Houghton Mifflin Company