Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Golden_4_Life on July 07, 2015, 12:39:04 PM
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We are tasked with testing the pH of a series of oil samples that have undergone various levels of imposed oxidation.
The oil is a Capric Oil (C-8?) and had been exposed to open air and or hydro peroxide for 0 days, 1 day, 3 days, 5 days and 10 days. So, the expectation is that the oil had become degraded (i.e., increased acidity). The project sponsor gave us some crappy test method that says: "...use 10 mL of water and 10 mL of oil sample, shake 5 minutes, then recover the oil layer, and add 100 uL of KCl, then test for pH." But, all the readings are turning out the same result of pH = 5.3. It says that the day 0 pH should be betw 6.0 and 7.5 pH; however, we are getting for day 0 a pH value of 5.2 and it is not stablilizing. We are using a wide/open junction pH electrode.
This is a erroneous test method, as first of all, isn't it atypical to even test for oil pH because pH is a function of ion flow in aqueous medium? Yet we are pulling the aqueous laye and still don't get a sensible result. Anybody confused?
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This is a erroneous test method, as first of all, isn't it atypical to even test for oil pH because pH is a function of ion flow in aqueous medium? Yet we are pulling the aqueous laye and still don't get a sensible result. Anybody confused?
Nothing confusing here, apart from the fact what you are testing is not the "oil pH" (even if it is called this way).
For checking the acidity of non-aqueous substances (like oils, soil, meat) we often use a method like the one you have described. It doesn't tell what is a real pH of the substance, but it allows comparing samples as to which are more and which are less acidic.
Compare soil measurement procedure outlined here: http://www.ph-meter.info/pH-measurements-other-procedures
No idea why you don't observe pH changes though, that's a completely separate issue.