Purpose
To demonstrate oxidation and reduction through observing the color changes of the various solutions.
Data
Part
Part I Part II |
Observations
When 10mL of potassium thiocyanate solution was added to two beakers, KMnO4 and H2O2, containing 0.43g of solution of ferrous ammoniumsulfate, both beakers's color turned to light orange. On one beaker, 10mL of potassium permanganate solution was added to the KMnO4 beaker and the KMnO4 solution turned to a color of dark purple. On the other beaker, 10mL of the hydrogen peroxide solution was added to the H2O2 beaker and the H2O2 solution turned to a color of less opaque, but dark purple as well. When stannous chloride solution was added to each beaker while mixing, the solutions turned clear, losing their color. Yellow-white precipitate was formed in KMnO4 solution beaker. 50mL of potassium hydroxide solution was added to 200mL of de-ionized water in a stoppered flask. When 5g of dextrose and several drops of methylene blue solution were added to the 200mL solution and mixed, the solution turned to the color of dark blue. After 5-10 minutes of rest, the solution became clear. When the flask was shaken again, the solution slowly regained its dark blue color. |
Conclusion
For part I, 0.4% solution of ferrous ammonium sulfate was prepared by dissolving 0.4g in 6M sulfuric acid. The solution was diluted to 100mL. 50mL of the ferrous ammonium sulfate solution were added to each of two labeled beakers. They were labeled KMnO4 and the other, H2O2. 10mL of the potassium thiocyanate solution were added to each of the beaker. The color of the solutions in the beaker turned to light orange. 10mL of KMnO4 and of H2O2 were added to their respective flasks. Both solution turned to a color of dark purple. After the color change, stannous chloride solution was added to each beaker while mixing, making the solutions turn clear and lose their color. Yellow-white precipitate was formed in KMnO4 solution beaker.
For Part II, 50mL of potassium hydroxide solution was diluted to 200mL of de-ionized water in a stoppered flask. 5g of dextrous was dissolved in the 200mL solution. Then several drops of methylene blue solution were added and it was mixed to create a dark blue solution. After 5-10 minutes of rest, the solution became clear. When the flask was shaken again, the solution slowly regained its dark blue color. After many repetitions, the color eventually stopped forming and the solution was left colorless.
For Part II, 50mL of potassium hydroxide solution was diluted to 200mL of de-ionized water in a stoppered flask. 5g of dextrous was dissolved in the 200mL solution. Then several drops of methylene blue solution were added and it was mixed to create a dark blue solution. After 5-10 minutes of rest, the solution became clear. When the flask was shaken again, the solution slowly regained its dark blue color. After many repetitions, the color eventually stopped forming and the solution was left colorless.
Discussion of Theory
Oxidation and Reduction are the transfer of electrons. Oxidation is the loss of electrons and reduction is the gain of electrons. The oxidized substance is the reducing agent, and the reduced substance is the oxidizing agent. Electrons, however, are not used up, but rather transferred to form heat and electricity. One well-known use of reduction and oxidation in common lives is battery. Battery uses the transfer of electrons to provide electricity for small electronics. When all of the electrons are transferred to a point in which the electrons are balanced, the battery is "dead" and no longer produces electricity. The reduction-oxidation equation (redox) is used to understand the transfer of electrons. Sometimes, redox equations can be observed visually. In this lab, methylene blue was added with distilled water and dextrous. The clear solution would be stirred and the oxidation would transfer electrons to produce dark blue color. The solution would be kept undisturbed and the reduction would transfer electrons back to return to the clear solution. After multiple trials, the solution would no longer turn blue, because all of e- would have been used up, equally balanced between reactants and products.
Data Analysis Questions
1. Write the 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.
Fe2+ + MnO4- -> Fe2O3 + Mn2+
(8H+ + 5e- + MnO4- -> Mn2+ + 4H2O) x 2
(3H2O +2Fe2+ -> Fe2O3 + 2e- + 6H+) x 5
--------------------------------------------------------------
7H2O + 10Fe2+ + 2MnO4- -> 5Fe2O3 + 2Mn2+ + 14H+
2Fe2+ H2O2 -> Fe2O3 + H2O
3H2O + Fe2+ -> Fe2O3 + 2e- + 6H+
2H+ + 2e- + H2O2 -> H2O + H2O
-----------------------------------------------------------
2Fe2+ + H2O2 -> Fe2O3 + 4H+
2. Write the balanced ionic equation for the reduction reaction using stannous chloride.
SnCl2 + Fe2O3 -> SnO2 + FeCl2
6H+ + 2e- + Fe2O3 -> 2FeCl + 3H2O
2H2O + SnCl2 -> SnO2 + 2e- + 4H+
2H+(aq) + Fe2O3(s) + SnCl2(aq) -> 2FeCl2(aq) + SnO2(s) + H2O(aq)
2H+(aq) + Fe2O3(s) + Sn2+(aq) -> 2Fe2+(aq) + SnO2(s) + H2O(aq)
4. Explain what happens when the colorless solution of methylene blue is shaken.
When the colorless solution of methylene blue is shaken, bubbles and larger surface area of solution are formed, resulting in a rise of oxygen level in the methylene blue solution. The solution is oxidized and the colorless solution turns blue. When the solution is left alone, the oxygen level falls and the solution is reduced into colorless solution.
5. After 10-12 cycles the methylene blue solution no longer turns blue. Explain why this reaction eventually runs down.
The electron will eventually get used up and the solution. The lack of electron would eventually halt the reaction from forming.
Fe2+ + MnO4- -> Fe2O3 + Mn2+
(8H+ + 5e- + MnO4- -> Mn2+ + 4H2O) x 2
(3H2O +2Fe2+ -> Fe2O3 + 2e- + 6H+) x 5
--------------------------------------------------------------
7H2O + 10Fe2+ + 2MnO4- -> 5Fe2O3 + 2Mn2+ + 14H+
2Fe2+ H2O2 -> Fe2O3 + H2O
3H2O + Fe2+ -> Fe2O3 + 2e- + 6H+
2H+ + 2e- + H2O2 -> H2O + H2O
-----------------------------------------------------------
2Fe2+ + H2O2 -> Fe2O3 + 4H+
2. Write the balanced ionic equation for the reduction reaction using stannous chloride.
SnCl2 + Fe2O3 -> SnO2 + FeCl2
6H+ + 2e- + Fe2O3 -> 2FeCl + 3H2O
2H2O + SnCl2 -> SnO2 + 2e- + 4H+
2H+(aq) + Fe2O3(s) + SnCl2(aq) -> 2FeCl2(aq) + SnO2(s) + H2O(aq)
2H+(aq) + Fe2O3(s) + Sn2+(aq) -> 2Fe2+(aq) + SnO2(s) + H2O(aq)
4. Explain what happens when the colorless solution of methylene blue is shaken.
When the colorless solution of methylene blue is shaken, bubbles and larger surface area of solution are formed, resulting in a rise of oxygen level in the methylene blue solution. The solution is oxidized and the colorless solution turns blue. When the solution is left alone, the oxygen level falls and the solution is reduced into colorless solution.
5. After 10-12 cycles the methylene blue solution no longer turns blue. Explain why this reaction eventually runs down.
The electron will eventually get used up and the solution. The lack of electron would eventually halt the reaction from forming.