Calculation of KCl and KI from Potentiometric Halide Titration with Ag+

[MitsuShai]

Here's the experiment that I did: http://www.chem.uic.edu/fetzer/chem222/a…
from the first page to half of the second page.

How do I calculate the amout of KCl and KI in the solution?

The graph is suppose to be like a backwards S and it has two endpoints and I don't know how to do the calculations for it like finding the amount of KCl and KI in the unknown.
I know how to do it with regular acid-base titration, but I don't know how to do it with halide titration. And I don't think it's the same because everyone else is having trouble figuring it out.

[MitsuShai]

In lab, we were given a sample that contained an unknown amount of KI and KCl. We dissolved and diluted the sample to 100 mL's, then took a 25 mL aliquot. The aliquot was connected to a silver electrode (indicator) and pH meter (reference). We titrated with silver nitrate on mL at a time (shorter intervals around determined endpoints) to create a potentiometric graph with 2 endpoints - the first one for the disappearance of iodide, due to the lower solubility of AgI, and the second one for the disappearance of chloride. I'm not sure exactly how how to find the concentrations of KI and KCl. Any assistance would be appreciated.

Attached is an excel of the data/graph - the y axis is in milivolts and the x axis is in mL of 0.0712 M AgNO3.

Thanks!

http://img27.imageshack.us/i/quantu.jpg/

[Borek]

Link from your first post doesn't work.

In general it is very simple - start with reaction equations. This is a simple stoichiometry at work, nothing more fancy.

This site may be of help:

http://www.titrations.info/precipitation-titration

It doesn't discuss how to detect end points using ion sensitive electrodes, but it doesn't matter how the end point was detected.