Why Use a High Phenanthroline to Iron Mole Ratio in Iron Concentration Analysis?

[corinnab]

1. This is a question about a lab.
The absorbing solution used in the lab had a mole ratio of phen to Fe of 52.8:1
However, the complex [Fe(phen)3]2+ has a mole ratio of 3:1 for phen:Fe

[Fe(phen)3]2+ is a coloured complex and we were determing iron concentration in a tablet.

I don't understand why we used a solution with such a high mole ratio, would appreciate any help!

 

[corinnab]

EDIT: the ratio in the absorbing solution is 5.2:1 I made a mistake
So what i would like to know is why the excess 0-phenanthroline in the absorbing solution?

 

[chemisttree]

You were determining the unknown concentration of iron in the tablet and used an excess of the reagent to determine iron.