Chemistry calculation help please!

Hi, could someone please help me understand something about this question:

A student weighed out a 2.29 g sample of impure K3[Fe(C2O4)3].3H2O and dissolved it in water.This solution was added to a 250 cm3 volumetric flask and made up to 250 cm3 with distilled water.

A 25.0 cm3 portion was pipetted into a conical flask and an excess of acid was added. The mixture was heated to 60 ºC and titrated with 0.0200 mol dm–3 KMnO4 solution.

26.40 cm3 of KMnO4 solution were needed for a complete reaction.
In this titration only the C2O4 2– ions react with the KMnO4 solution
Write an equation for the reaction between C2O42– ions and MnO4– ions in acidic solution.

Calculate the percentage purity of the original sample of K3[Fe(C2O4)3].3H2O


I understand how to calculate this, but I really don't understand why the moles of C2O4 ions are divided by 3 once they are calculated.... I get there is 3 c2o4 ions in the impure sample but the idea of dividing by 3 does not make sense.


I would really appreciate it if someone could explain this please.

Same principle as with the other question you had: [Fe(C2O4)3]3- => Fe3+ + 3C2O4^2-