Mechanisms of Catalysis - The Intermediate Formation Theory
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Who suggested this theory?
Arrhenius
What did Arrhenius suggest in relation to the mechanisms of catalysis?
He suggested that a catalyst works by forming an intermediate compound i.e. One or multiple reactants combine with the catalyst to form an intermediate compound that may only exist for a very short time and may be difficult to detect
Give an example of a reaction which suggests Arrhenius’ Intermediate Formation Theory
The oxidation of potassium sodium tartrate using hydrogen peroxide which is catalysed by Co2+ ions
How does the oxidation of potassium sodium tartrate using hydrogen peroxide suggest Arrhenius’ theory is correct? (3 Key steps)
• The solution of potassium sodium tartrate and crystals of pink cobalt (II) chloride is pink at first • When some 100- volume hydrogen peroxide is added fizzing is observed and the solution becomes green • After a few seconds the solution ceases to fizz and the solution becomes pink again
What does the colour change from pink to green indicate?
That a new substance has been formed
What does the change of the green colour back to pink suggest?
That the new substance is an intermediate
What does the fizzing of the solution suggest?
That the intermediate is reacting
What does the restoration of the pink colour suggest?
That the Co2+ ions have not been used up
What suggests that a new substance has been formed?
The colour change from pink to green
What suggests that the new substance is an intermediate?
The change of the green colour back to pink
What suggests that the intermediate is reacting?
The fizzing of the green solution
What suggests that the Co2+ ions have not been used up?
The restoration of the pink colour
What is the source of the catalyst in this experiment?
Crystals of pink cobalt (II) chloride
What is the first step to this experiment?
Dissolving the potassium sodium tartrate in hot water with some crystals of pink cobalt (II) chloride