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Introduction

Experiment #13 SL December, 5/2002 Redox reactions AIM: The aim of this experiment is to deduce the oxidation state of manganese in several reactions according to the color change of the solution. INTRODUCTION: Manganese is a transition metal that exhibits several different oxidation states. Each oxidation state is characterized by a different color. Thus the presence of manganese in a particular oxidation state may be deduced by the color of the substance observed. So, the colors that will appear in each one of the magnesium's oxidation states will be as in the following table: OXIDATION STATE COLOR Mn (II) ...read more.

Middle

Then we add some drops of Na2SO3. In the same solution, we add a considerable excess of sodium sulfite. To the solution that solution, we add a few drops of HCl, until we observe a color change. We should be very careful when handling HCl and NaOH because they are very corrosive. Furthermore, HCl is fuming so we use it under the fume cupboard. KMnO4 is an oxidizing agent and very harmful. CALCULATIONS: MM(NaOH) = 40 n = c x v --> n = 3 x 0.05 = 0.15 moles m = 0.15 x 40 = 6g MM (KMnO4) = 158 n = 0.05 x 0.05 = 2.5 x 10-3 moles m = 2.5 x 10-3 x 158 = 0.139g MM(Na2SO3) ...read more.

Conclusion

MnO2 + HCl --> Mn+2 + Cl2 Oxidation states: Mn: 4 --> 2 Cl: -1 --> 0 Oxidising agent: HCl Reducing agent: MnO2 Initial color Final color 1 Purple Green 2 Green Black-brown precipitate 3 Black brown precipitate colorless In the second reaction, we may observe that the surface of the solution is transparent with some brown particles, whereas at the bottom of the beaker the solution is very dark brown/ black and a precipitate has formed. DATA ANALYSIS AND CONCLUSION: As it was state in the hypothesis, we expected to see different colors as the oxidation state of manganese changes. Manganese may gain or lose electrons when undergoes such reactions and thus its oxidation state changes and therefore we are able to see the difference in color. ...read more.

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