Explain why acidified potassium manganate(VII) is used as an oxidizing agent in the reaction of ethanol to ethanoic acid. What observations would you make during the reaction and what would these observations indicate?
Acidified potassium manganate(VII) (KMnO4) is used as an oxidizing agent in the reaction of ethanol to ethanoic acid because it has a high oxidizing potential. This means it readily accepts electrons from other substances, causing them to be oxidized. In this case, it oxidizes ethanol to ethanoic acid.
The reaction is carried out in an acidic solution (typically dilute sulfuric acid). The acid is essential for the following reasons:
- Provides H+ ions: The acid provides hydrogen ions (H+) which are required for the oxidation process.
- Maintains a suitable pH: The acidic conditions help to maintain a pH that is optimal for the reaction to proceed.
During the reaction, several observations can be made:
- Colour Change: The purple colour of the potassium manganate(VII) solution will fade as it is reduced to manganese(II) ions (MnO2). This fading indicates that the oxidation reaction is occurring.
- Formation of a Black Precipitate: A black precipitate of manganese(II) oxide (MnO2) will form. This precipitate is a characteristic sign of the reduction of manganate(VII) to manganate(II).
- Release of Heat: The reaction is exothermic, meaning it releases heat. This can be observed by a slight increase in the temperature of the solution.
These observations indicate that the oxidation of ethanol to ethanoic acid is taking place. The fading of the purple colour and the formation of the black precipitate are direct evidence of the reduction of manganate(VII) to manganate(II), confirming that the reaction is proceeding as expected.