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Chemistry - pH


Let me preface this blog with a disclaimer - - I am not a chemist.  My understanding of the subject of pH is only as it relates to industial cleaning, cleaning chemistries and their application.  Over the years, I have been associated with many chemists who have been very helpful in their efforts to advance my understanding of pH.  I have learned a great deal from them but fear that the big picture is beyond my comprehension.  As is the case with so many of the widely varied disciplines that touch industrial cleaning, I have retained mostly that information that was applicable to my specific and somewhat limited needs which is what I will share with you in the next several blogs.
The pH of several common materials. More alkaline materials are at the top while more acid materials are at the bottom. The pH of pure water is close to 7.

In technical terms, pH is the negative logarithm of the activity of the (solvated) hydronium ion, more often expressed as the measure of the hydronium ion concentration. (Thank you Wikipedia!)

In more simple terms, pH is a measurement of the acidity or alkalinity of a liquid solution.  The illustration at the right shows the pH of several liquids many of us encounter daily.  On this scale, acidic materials are found near the bottom while alkaline (basic) solutions are near the top.  One important thing to know about pH is that is a logarhythmic scale.  This means that each unit increase in pH indicates a ten-fold increase (or decrease) in activity from that of the previous level unit. PH is important in cleaning especially as it pertains to cleaning solutions.  Many aqueous cleaning chemistries use acids or bases of various types and in varying strengths as the base or their formulation. Some substrates we clean are sensitive to attack by bases and acids.  Aluminum, for example is readily and rapidly attacked by alkaline materials.  Acids, on the other hand, attack many metals including steel.  Contaminants, likewise, are affected in different ways by chemistries of varying pH.  Alkaline formulations typically excel at removing hydrocarbons while acids are great for removing oxides.  Generalizations, however, are dangerous! PH is a property that can be measured in many ways.  Most of us remember the red and blue litmus paper we used in chemistry class.  If red litmus paper turned blue, the material was basic - - if blue litmus paper turned red, it was an acid.  Certainly, there were techniques that would do more than indicate if a material was an acid or a base but they were much too complicated.  Today, red and blue litmus papers have been replaced by similar paper strips which turn a wide range of colors depending on pH and can rather accurately measure pH at least to the nearest unit.  There are also electronic devices that have probes that can accurately measure pH.  They are available in both permanent mount and hand-held versions.  The availability of these more accurate measuring devices has, if nothing else, made us more aware of and dependent on pH measurements to control chemical concentrations and other variables in industrial cleaning processes. As with any tool, pH measurement must be properly applied to be useful.  The next blog will address the benefits and possible shortcomings of using pH measurements in industrial cleaning.

- FJF  -