Photo AI
Define oxidation number - Leaving Cert Chemistry - Question d - 2001
Question d
Define oxidation number. In a laboratory experiment, carried out at room temperature and pressure, a student added 1 cm³ of a solution of potassium manganate(VII) t... show full transcript
Worked Solution & Example Answer:Define oxidation number - Leaving Cert Chemistry - Question d - 2001
Step 1
Explain clearly why the decolorising time became shorter when the second portion of the potassium manganate(VII) solution was added.
Answer
The observation that the decolorizing time becomes shorter upon adding the second portion of potassium manganate(VII) solution can be explained by the behavior of the catalyst produced in the reaction. Manganese(II) ions produced from the reduction of potassium manganate(VII) act as a catalyst in this reaction.
When the first portion of potassium manganate(VII) is added, the reaction proceeds, and some time is taken for the purple color to disappear as the oxidizing agent reacts with the ethanedioic acid. However, once the manganese(II) ions are formed, they can facilitate the oxidation of ethanedioic acid more efficiently. The presence of these manganese(II) ions can lower the activation energy required for the reaction, thereby speeding it up.
Consequently, when the second portion of potassium manganate(VII) solution is introduced, there is already a sufficient amount of manganese(II) ions present. This enhances the reaction rate even more, resulting in a shorter time for the purple color to decolorize.