Selected Redox Reactions

SELECTED REDOX REACTIONS

A.J.F. CAGUNTAS

1 DEPARTMENT OF CHEMICAL ENGINEERING, COLLEGE OF ENGINEERING

UNIVERSITY OF THE PHILIPPINES, DILIMAN, QUEZON CITY, PHILIPPINES

DATE PERFORMED: MAY 15, 2013

INSTRUCTOR’S NAME: SIR MARO R. PEÑA

RESULTS AND DISCUSSION

Na2SO3 and KMnO4 react with each other differently in various media.

If the reaction occurs in an acidic medium, the following half reactions can be observed:

|Reduction |Oxidation |

|MnO4-(aq) + 8H+(aq) + 5e- → |SO32-(aq) + H2O(l) → SO42-(aq) + |

|Mn2+(aq) + 4H2O(l) |2H+(aq) + 2e- |

The overall net ionic equation of the said reaction in acidic medium is as follows:

6H+(aq) + 5SO32-(aq) + 2MnO4-(aq) → 2Mn2+(aq) + 5SO42-(aq) + 3H2O(l)

The resulting solution would be colorless, with neither complex nor precipitate. It is also known that Mn2+ is faint pink in solution, but said color did not appear due to the low concentration of KMnO4.

In a neutral medium, the following half reactions could be observed:

|Reduction |Oxidation |

|MnO4-(aq) + 2H2O(l) + 3e- → |SO32-(aq) + 2OH-(aq) → SO42-(aq) |

|MnO2(s) + 4OH-(aq) |+ H2O(l) + 2e- |

The overall net ionic equation of the reaction in neutral medium is as follows:

H2O(l) + 3SO32-(aq) + 2MnO4-(aq) → 3SO42-(aq) + 2MnO2(s) + 2OH-(aq)

Notice that MnO2 is produced in the reaction. This is the brown precipitate which can be seen during the experiment.

In basic medium, the following half reactions could be observed:

|Reduction |Oxidation |

|MnO4-(aq) + e- → MnO42-(aq) |SO32-(aq) + 2OH-(aq) → SO42-(aq) |

| |+ H2O(l) + 2e- |

The overall net ionic equation of the reaction in basic medium is as follows:

2OH-(aq) + SO32-(aq) + 2MnO4-(aq) → SO42-(aq) +...