Oxidation-Reduction Reactions Lab
Purpose
The purpose of the lab is to record and observe changes the solution undergoes during the transfer of electrons in the oxidation-reduction reaction. In order to determine the affects this transfer has on the solution, observations will be recorded after each step of the oxidation-reduction reaction.
Data Table
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Observations |
Part I
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The addition of potassium thiocyanate caused both solutions to turn a rusty, transparent peach/orange color. The addition of KMnO4 to the KMnO4 beaker caused the solution to turn a dark red color. The same thing occurred when H2O2 was added to the beaker labeled H2O2. Once the stannous chloride was added, both solutions turned light red. There appeared to be no precipitate formation in either beakers.
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Part II
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Once the methylene blue was added to the solution, it turned a dark, vibrant blue. After 20 minutes had passed, the solution was lighter than the original blue. The solution was stirred vigorously until the solution returned to its oxidized state, the bright blue.
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Conclusion
During the first part of the lab, observations were recorded to identify the transfer of electrons as the compounds got oxidized/reduced. Both solutions of hydrogen peroxide and permanaganate became lighter after stannous chloride was added. In the solution with Fe2+ and hydrogen peroxide, hydrogen peroxide got reduced and Fe2+ got oxidized. In the solution with Fe2+ and permanganate, permanganate got reduced and Fe2+ got oxidized. The second part of the lab was demonstrating limiting reactants and redox reactions. The solution of methylene blue was reversed by vigorously shaking the flask until the solution became blue again. Blue indicates that the solution is being oxidized.
Discussion of Theory
This lab demonstrated oxidation-reduction reactions. Oxidation is the gain of oxygen and reduction is the loss of oxygen. Oxygens gain electrons from the reactant that it is reacting with. Oxidation-reduction reactions can occur without the presence of oxygen. In this case, the oxidized compound loses electrons and the reduced compound gains electrons from the oxidizing agent. Reduction potential values can help determine the oxidizing power of the compound. The more positive the potential, the greater the affinity for electrons and tendency to be reduced. In order to caluculate the amount of electrons that are transferred, the two half reactions for the oxidzed compound and the reduced compound must be written. First, take the oxidize or reduced compound on the reactant side and write the reaction. Then balance the number of atoms, add the number of transferred electrons (atoms times electrons transferred) to the side with the highest charge, and add H+ and H2O where needed. The balanced ionic equations for Fe2+ and hydrogen peroxide was H2O + Fe(2+) + H2(O2) yields Fe2(O3) + 4H+ and the reaction for Fe2+ and permanganate was 5Fe(2+) + 8H(+) + Mn(O4) yields Mn(2+) + 5Fe(3+) + 4H2O. Hydrogen peroxide and permanganate were reduced in both cases. The evidence to support this was the color change. Oxidation of an Fe2+ containing compound to Fe3+ when thiocyanate is added forms a red color. Both solutions turn dark red, which indicates Fe2+ was oxidized. When one atom loses an electron, another must gain the electron. Therefore, if Fe2+ lost an electron the oxidizing agent (hydrogen peroxide and permanganate) must gain an electron.
The second part of the lab also demonstrated oxidation-reduction reactions. A 50 mL of Potassium Hydroxide Solution was diluted to 200 mL with de-ionized water. Then 5g of glucose and several drops of methylene blue was add to this solution. This resulted in a vibrant, deep blue color. After approximately 20 minutes the solution was becoming clear. Using a stirring rod, the solution was mixed vigorously until it returned to blue. Vigorously stirring the solution allowed oxygen gas to be introduced into the solution. Since oxidation is the gain of oxygen, the solution turned to blue. The dye methylene blue turns to a deep blue color when oxidized. However, if this step is repeated 5-10 more times, it will eventually run down. The electron is acting as a limiting reactant. Even though, oxygen gas is in abundance (loses electrons), there must be a atom that gains the electrons oxygen gives off. If all the atoms in the solution have been reduced, oxidation can not occur.
The second part of the lab also demonstrated oxidation-reduction reactions. A 50 mL of Potassium Hydroxide Solution was diluted to 200 mL with de-ionized water. Then 5g of glucose and several drops of methylene blue was add to this solution. This resulted in a vibrant, deep blue color. After approximately 20 minutes the solution was becoming clear. Using a stirring rod, the solution was mixed vigorously until it returned to blue. Vigorously stirring the solution allowed oxygen gas to be introduced into the solution. Since oxidation is the gain of oxygen, the solution turned to blue. The dye methylene blue turns to a deep blue color when oxidized. However, if this step is repeated 5-10 more times, it will eventually run down. The electron is acting as a limiting reactant. Even though, oxygen gas is in abundance (loses electrons), there must be a atom that gains the electrons oxygen gives off. If all the atoms in the solution have been reduced, oxidation can not occur.
Data Analysis Questions
Question 1 - Write a balanced ionic equations for the oxidation of iron with permanganate and hydrogen peroxide. Explain any differences observed in the oxidizing power of the two oxidizing agents.
Hydrogen peroxide has a higher oxidizing power than permanganate because it has a higher reduction potential. Because hydrogen peroixde has a higher reduction potential, it is more likely to be the reduced and permanganate has a lower reduction potential, so it is more likely to be the oxidized. The more positive the potential, the greater the affinity for electrons and tendency to be reduced.
Question 2 - Write the balanced ionic equation for the reduction reaction using stannous chloride.
Question 4 - Explain what happens when the colorless solution of methylene blue is shaken.
When the colorless solution of methylene blue is shaken, the solution returned to its original dark blue. When the solution was vigorously shaken the oxygen from the atmosphere was introduced into the solution, causing it to oxidize. Since the oxidation of methylene blue results in a deep blue, the solution turned blue again.
Question 5 - After 10-12 cycles the methylene blue solution no longer turns blue. Explain why this reaction eventually runs down.
The reaction eventually runs down because oxidation must be accompained by reduction and evetually all that can be oxidized or reduced will be oxidized or reduced completely. This demonstrates limiting reactants (electrons).