One of the most popular methods for determine trace amounts ofwater is a coulometric titration, called the Karl Fischer.Measuring trace amounts of water is one of the most challenginganalytical methods.
a) What would be another method that would measure largeramounts of water contained in a sample, and how would you doit?
b) The Karl Fischer method is a secondary coulometric analysisthat utilizies the generation of I2/I3 with starch, just like youdid in lab, generated from the Iodide ion. This iodine molecularspecies then reacts with water in a complicated Redox, involvingstinky pyridine....hense, the advantage of doing this by remotecontrol under a hood. The actual limiting reagent is WATER: Onemole of water reacts with one mole of generated I3.
The goal of your problem is to find the ppm of water in a 250 mLsample of pure ethanol, that has a density of 0.7893 g/mL. Acurrent of 55.5 milliamps was run for 4 minutes 23 seconds, untilthe blue/black color of the starch was observed. However, thecurrent generator box was only 89.3 % current efficient, losingsome current. The electrochemical production of the tri-iodide ionreagent was the same oxidation reaction as in lab. What is the ppmof WATER contamination the 250 mL of pure ethanol?
