Looking at the stoichiometry of the reaction (see the lab manual), how many moles kmno4 must have been delivered by the buret to react with that much fe(nh4)2(so4)2 · 6h2o? 8h+ + 5fe+2 + mno4 - --> mn+2 + 5fe+3 + 4h2o

8H⁺ + 5Fe²⁺ + MnO₄⁻ ⇒ Mn²⁺ + 5Fe³⁺ + 4H₂O 

According to the reaction, Fe²⁺ and MnO4⁻ have following stoichiometric ratio:

n(Fe²⁺) : n(MnO4⁻) = 5 : 1

n(MnO4⁻) = n(Fe²⁺) / 5

So, for each mole of Fe²⁺ it is needed 1/5 moles of MnO4⁻.

Answerhund's rule;

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