[Strike]

Hello,

I did an experiment where we would titrate iron ore that was reduced to Fe²⁺ with SnCl₂. So the solution went from yellow-orange to colourless before the titration began. At the first end-point the solution was pale yellow and progressively got darker in yellow as the titration went on. So now the solution is mostly Fe(III).

One of the parameters we had to calculate was the Fe(III)/Fe(II) ratio in the original solution. We did two titrations and the first had a ratio of ~30 but the second was ~50.

The TA said that the precision and accuracy of these calculations is not very reliable and most students will find that the ratio in the second sample is higher. Why is this?

[Borek]

It is not clear to me what you did and what is the "original solution" - one before the reduction with tin? If so, how do you calculate the ratio?

Was your solution containing Fe²⁺ in contact with atmospheric oxygen?