Transition Metals - Autocatalysis of Transition Metals (A-Level Chemistry)

Autocatalysis of Transition Metals


Manganate (VII) ions react with ethanedioate ions. The reaction is very slow to start with as both ions are negative, and have a high activation energy.

The reaction is catalysed by Mn²⁺ ion, which are formed in the reaction.

2MnO₄⁻ (aq) + 8H⁺(aq) + 5C₂O₄²⁻(aq) → 2Mn²⁺(aq) + 4H₂O(l) + 10CO₂(g)

The Mn²⁺ ions produced are oxidised by the MnO₄⁻ ions to form Mn³⁺ ions.

This reaction is faster because the Mn²⁺ ions are positive and the MnO₄⁻ ions are negative ions.

2MnO₄⁻ (aq) + 8H⁺(aq) + 4Mn²⁺(aq) → 5Mn³⁺(aq) + 4H₂O(l)

The Mn³⁺ ions react with the ethanedioate ions to reform the Mn²⁺ ions.

Again this reaction is faster because the Mn³⁺ ions are positive and ethanedioate ions are negative.

2Mn³⁺(aq) + C₂O₄²⁻(aq) → 2CO₂(g) + 2Mn²⁺(aq)

The Mn²⁺ ions are not present at the start of the reaction, and the rate is very slow. Once the Mn²⁺ ions form, the rate of reaction occurs much faster, as the Mn³⁺ ions is produced to react with ethanedioate ions.

This phenomenon in which the products of a reaction act as catalysts for that same reaction is known as autocatalysis.

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