[lazipeter]

1. Fe2+ or Fe3+ act as homogeneous catalyst in the reaction:
I2(aq) + 2 S2O3(aq) 2 I-(aq) + S4O6(aq)

2. Mn2+ acts as an autocatalyst in the reaction:
10 I-(aq) + 2 MnO4-(aq) +16 H+(aq) 5 I2(aq) + 2 Mn2+(aq) + 8 H2O(l)

they are wrong, why??

thanks!!

[sjb]

What is the definition of a catalyst?

[lazipeter]

Sth can provide an alternative reaction route with smaller activation energy so that the reaction rate becomes faster.
Fe3+ or Fe2+ can react with the reducing agent and oxidizing agent subsequently by means of changing its oxidation states, and Mn2+ can also have variable OS so why they're wrong??
Moreover Fe2+, Fe3+ are postively charged so I think they should attract the reactants so Fe2+,Fe3+ should be able to be the catalyst.