Distillations with Karl

This week has been a little been convoluted. I originally intended to trying repeating the density experiment with ultra-pure ethanol in order to validate that the liquid cell is allowing for contamination of atmospheric H2O in our more volatile and hydrophilic solutions (if you remember from last time we proved that either our methanol was either absorbing atmospheric H2O or allowing for the evaporation of methanol, concentrating our H2O already present in the methanol solution). I learned that most reagent grade ethanol has some H2O in solution, 1-4% wt/wt depending on the time spent of the shelf, but what I also learned is that ethanol/water solutions have an azeotrope point at about 95% ethanol meaning that a distillation would be particularly ineffective in purifying our ethanol further. Given my organic experience I knew that MgSO4 could be used to dry solutions, but could not find out to what degree they would so. I looked into some more common/complicated purification processes to produce ultra-pure ethanol, the most viable being adding small amount of benzene to the ethanol to alter the azeotropic point of the ethanol/water solution to allow for a 100% purification, but this would result in a contaminate of benzene into our ethanol solution and possible alter our densities significantly. And in the case of introducing one invasive species to get rid of another invasive species, I feared that I would end up introducing far more complexity to my experiment without knowing the eventual results. I decided to wait until I could talk to Allison before I continued.

Allison decided to reanalyze our problem in the face of this next complexity, and has decided to treat the liquid cell as if we have proven it to allow for contamination from atmospheric H2O. Given this she has decided to shift my focus from proving that the liquid cell is absorbing atmospheric H2O to designing a Karl-Fischer Titration.

For those reading this who are unaware of what a Karl-Fischer titration is I will attempt to summarize it ever so briefly. A Karl-Fischer titration utilizes the electrolysis of water with dissolved aqueous iodine to produce an iodine ion. The measurement of the concentration of iodine ions is done by taking the potential difference across the system. We can imagine that the higher the concentration of iodine ions would result in a higher voltage between the two electrodes, and the concentration of iodine directly reflects the amount of H2O present.

Now this is, of course, a simplification of this process. The nuances between two types of Karl-Fischer titrations come between whether you are using your using your desired solution as a titrant (volumetric Karl-Fischer titrations) in the typical understanding of a titration, or simply adding a given amount and using the change in voltage to estimate your solution’s water concentration. Although the volumetric KFT is significantly easier to implement it measures accurately only the scale of 1-100% wt/wt water concentration, the calorimetric approach allows for accuracy up to 1microgram to 10miligrams roughly, which is the range we intend to work with.

I will be first to admit I do not fully understand the process or the nuances, and need significantly more time before I can even think about ordering parts. I may end up looking back on this and realize that I had completely misunderstood a topic or distinguishing characteristic. I am hoping to have a basic diagram and outline by next week, and maybe start ordering parts two weeks fro


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