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Manganese compounds demonstrate different oxidation states, including +7, +6, + 4, +3 and +2. +7 is the maximum oxidation state of Manganese. A manganese compound where the manganese element is in oxidation state +7 is a very strong oxidizing agent. This report presents a lab experiment conducted using the Late Nite Labs (latenitelabs.com).
Purpose of the lab
The purpose of this lab is to study the various oxidation states of manganese. It specifically examines the reduction of MnO4– (permanganate ion) by HSO3– (bisulfite ion) under acidic, basic, and neutral conditions.
Outline of the procedures
- 5 clean test tubes were taken from the Glassware shelf and placed them on the workbench.
- 5 ml of water were added to the first test tube, which was the color standard against which the pale pink Mn+² ion would be compared.
- 5 ml of KMnO4 were added to the second test tube, which was the color standard for the purple permanganate ion.
- 2 ml of KMnO4 were then added to test tubes 3, 4, and 5.
- 1 ml of NaOH were added to test tube 3.
- 1 ml of H2SO4were added to test tube 5.
- 3 pH meters were then taken from the Glassware shelf and placed into test tubes 3, 4, and 5.
- The pH in the test tubes was recorded appropriately.
- Test tube 3 was the basic solution, test tube 4 was neutral, and test tube 5 was acidic.
- Five 1 ml increments of NaHSO3 were added to test tube 3 and observation made, and the results of the reaction (color, precipitation, pH) were recorded after each addition of 1 ml.
- Five 1 ml increments of NaHSO3 were also added to test tube 4, an observation made, and the results of the reaction (color, precipitation, pH) recorded after each addition of 1 ml.
- Finally, five 1 ml increments of NaHSO3 were added to test tube 5, an observation made, and the results of the reaction (color, precipitation, pH) recorded after each addition of 1 ml.
Data collection section
For each test tube, test tube 3, test tube 4, and test tube 5, the final results of the chemical reactions are shown in table 1 below. Note that initially, the initial color of the solutions is purple, there is no precipitate, and the pH for test tube 3, 4 and 5 are 13.82, 7.00, and 0.00 respectively.
Table 1:Results of the reactions.
|Test tube 3||Test tube 4||Test tube 5|
|Color of the solution||Green||Colorless||Pale Pink|
|Color of the precipitate||no precipitate||black||no precipitate|
|pH of each test tube||13.35||7.35||0.14|
An oxidation states table with the oxidation numbers of Mn (from the potassium permanganate [KMnO4]) and S (from the sodium bisulfate [NaHSO3]) before and after the reaction in each test tube.
Table 2: Oxidation States Table.
|Test Tube||Oxidation Number Mn Before||Oxidation Number Mn After|
|3||+ 7||+ 6|
|4||+ 7||+ 4|
|5||+ 7||+ 2|
|Oxidation Number S Before||Oxidation Number S After|
|3||+ 4||+ 6|
|4||+ 4||+ 6|
|5||+ 4||+ 6|
Discussions and conclusions
The reduction process of the permanganate ion can be presented in ionic equations. The net ionic equations for the redox reactions in each test tube of the lab is as shown below.
- Test tube 3:
2MnO4– + 2OH– + SO32- => H2O + 2MnO42- + SO42-
- Test tube 4:
2MnO4– + 3HSO3– => 2H2O + 3SO42- + 2MnO2
- Test tube 5:
2MnO4– + H+ + 5HSO4– => 3H2O + 2Mn2+ + 5SO42-
We have seen that the permanganate ion is a good oxidizing agent. The substance, permanganate, is a good oxidizing agent because it has Manganese in its highest oxidation state, such that it effectively removes electrons from other substances during a redox reaction. It is worth to note that redox refers to an reduction-oxidation chemical reaction (Kelter, Mosher & Scott, 2007, p.864). The Manganese in the permanganate ion has all the electrons from the 3s and 4s orbitals removed.
Oxidation is a chemical reaction that involves removal of an electron or electrons from a substance. An oxidation reaction always involves a corresponding reduction reaction (Kelter, Mosher & Scott, 2007, p.12). The substance that receives the electrons is then reduced. Therefore, reduction is a chemical reaction where an electron or electrons are added to a substance.
An oxidizing agent is a substance that takes out electrons from another substance during a reduction-oxidation reaction. After the redox reaction, an oxidizing agent is reduced. For instance, in the reaction involving MnO4– (permanganate ion) and HSO3– (bisulfite ion) the permanganate ion acts as an oxidizing agent. A reducing agent is a substance that is involved in redox reaction that contributes an electron to another substance. A reducing agent is oxidized during a redox reaction. For instance, in the reaction involving MnO4– (permanganate ion) and HSO3– (bisulfite ion) the bisulfite ion acts as a reducing agent.
Kelter, P.B., Mosher, M. & Scott, A. (2007). Chemistry. Cengage Learning.
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Late Nite Labs. (2006). Oxidation States of Manganese. Web.