[ahhppull]

I have to make up a lab because of hurricane sandy.  My TA gave me the data, but the actual experiment was not performed, so I have no idea how to do this.

An iron supplement tablet weighing 2.5091 (±0.0001) g was crushed and boiled in 25.00 mL of 6 M hydrochloric acid.
After boiling and cooling, the solution was filtered, and the pH of the filtrate was adjusted to a value of 3.5. The solution
was then diluted to 250mL (call this solution A).

A standard solution of iron(II) ammonium sulfate (Fe(NH4)2(SO4)2) was prepared by dissolving 315.1 mg in 1.000 L of
water (call this solution B).

Six 100-mL volumetric flasks were used to prepare a series of solutions (numbered 1-6). All 6 solutions contained 2.00
mL of 0.100 M phenanthroline (an excess amount) and 5.00 mL of solution A. Then varying amounts of solution B were
added (see table below), and finally, the solutions were diluted to the mark. The absorbance of each solution is given in
the table below. All transfers were performed with volumetric pipets.

The table he gave us is a table of volumes of B and Absorbance
0mL - 0.3996
3 mL -0.5453
6 mL -0.6525
9 mL - 0.7605
12 mL -0.8909
15 mL -0.9989

I plotted the graph, and the equation came to be y = 0.0394x + 0.4123

I need to find the weight % of Fe.  I tried to look this up in my textbook, but it doesn't help.  When I searched it online, they had several ways of finding the concentration of the unknown.  One way was that the y-intercept is the concentration and another way is that when the absorbance is 0, that is the concentration of unknown.  What is the correct method?

[ahhppull]

Nevermind, ignore this thread.  I got the answer now.

[plateeny]

Hi

by the way how you calculated the concentration of unknown by standard edition method through the linear equation  y = 0.0394x + 0.4123

[Borek]

First: think what x and y are.