Selected Redox Reactions

Topics: Redox, Zinc, Oxidizing agent Pages: 5 (1161 words) Published: July 15, 2013
SELECTED REDOX REACTIONS

RESULTS AND DISCUSSION
Oxidation-Reduction reaction also known as redox reaction is a process in which there’s a net movement of electrons between reacting species. These types of reactions involve two separate elementary reactions: one that loses electrons and another that gains the electrons that was lost. Gaining of electrons is referred to as Reduction reaction (the species that undergoes reduction is called as oxidizing agent) while losing of electrons is called Oxidation reaction (the reducing agent is the species that undergoes oxidation).

In this experiment, seven different set-ups were made which were eventually divided into three different groups. Group 1, those on Part A, were set-ups that investigated the reaction of the permanganate (MnO4-) ion in different media. Group 2, those on Part B, were set-ups that were done in order to study the reaction of Fe(SCN)2+ ion with that of elemental zinc. While the last, Group 3, those on Part C were set-ups that investigated the reaction of Fe4[Fe(CN)6]3 with that of elemental zinc.

Group 1, test tubes A to C, vary greatly from each other. This is probably because they differ in the medium used for the reaction to took place. In test tube A, brown precipitate, MnO2, was observed. The reaction was then supported by the equations displayed below:

Test Tube A (Neutral Media)
Reduction Rxn:
2(MnO4- + 4H+ + 3e-) -> (MnO2 + 2H2O)2
Oxidation Rxn:
3(SO32- + H2O) -> (SO42- + 2H+ + 2e-)3
Net Ionic Eq’n:
2MnO4-(aq) + 3SO32-(aq) + 2H+(aq) -> 2MnO2(s) + 3SO42-(aq) + H2O(l)

In test tube B, in which the reaction was done in acidic medium, it was observed that there’s no visible reaction. In this reaction, Mn2+ ion was formed. This ion is colorless and supposedly the solution will turned out to be colorless. It could be that Mn2+ produced was too small that it was not observable at all. This observation was supported by the equations below:

Test Tube B (Acidic Media)
Reduction Rxn:
2(MnO4- + 8H+ + 5e-) -> (Mn2+ + 4H2O)2
Oxidation Rxn:
5(SO32- + H2O) -> (SO42- + 2H+ + 2e-)5
Net Ionic Eq’n:
2MnO4-(aq) + 5SO32-(aq) + 6H+(aq) -> 2Mn2+(aq) + 5SO42-(aq) + 3H2O(l)

In test tube C in which the used medium was basic, it was observed that a green precipitate was formed and then it was soon changed to brown precipitate. The green precipitate that was observed in the reaction may be due to the presence of MnO42- which is a dark green color solution. While the brown precipitate could be due to the mixture of MnO42- to either MnO4- (deep violet) or MnO43- (deep blue) ions. The formation of MnO42- was supported by the equations below:

Test Tube C (Basic Media)
Reduction Rxn:
2(MnO4- + e-) -> (MnO42-)2
Oxidation Rxn:
SO32- + H2O -> SO42- + 2H+ + 2e-
Net Ionic Eq’n:
2MnO4-(aq) + SO32-(aq) + 2OH-(aq) -> 2MnO42-(aq) + SO42-(aq) + H2O(l)

Test tube D in Group 2, was observed to form a blood red complex, FeSCN2+, which was supported by the equation:

Test Tube D
Fe3+(aq) + SCN-(aq) -> FeSCN2+(aq)

Test tube D acted as a control solution for test tube E so that we observe the changes in the solution after adding elemental zinc. In test tube E, it was observed that the solution changed to orange then to yellow. And lastly, it was observed to have a dark orange precipitate in a colorless solution. We can say that there really was a reaction that happened between FeSCN2+ and Zn because as what we have observed, the intensity of the color of the solution decreased (breaking down of FeSCN2+ to Fe3+ and SCN- ions) which also imply that there’s dissolution of Zn metal. The reactions that happened are presented below:

Test Tube E
Reduction Rxn:
2(FeSCN2+ + e-) -> (SCN- + Fe2+)2
Oxidation Rxn:
Zn -> Zn2+ + 2e-
Net Ionic Eq’n:
Zn(s) + 2FeSCN2+(aq) -> Zn2+(aq) + 2Fe2+(aq) + 2SCN-(aq)

The last group, Group 3 which was composed of test tube F and G was somehow similar to that of Group 2. Test tube F was observed to form a prussian blue...

References: Advameg, Inc., 2013. Manganese. In Chemistry Explained: Foundations and Applications. Retrieved March 20, 2013 from, http://www.chemistryexplained.com/elements/L-P/Manganese.html
De Vera, G., (n.d.) Selected Redox Reactions. In Scribd. Retrieved March 20, 2013 from, http://www.scribd.com/doc/87950627/Selected-Redox-Reactions-Ppt
Petrucci, R.H., Harwood, W.S., Herring, F.G. General Chemistry: Principles and Modern Applications 8th ed. Pearson Education South Asia Pte. Ltd. Singapore 2004
Silberberg, M.S., Chemistry: The Molecular Nature of Matter and Change 5th ed. McGraw-Hill Companies, Inc., New York 2009
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