“Propagation of an Error: The pKa of Water is not 15.7”
Abstract: Many organic chemistry textbooks, tables, and papers state that the pKa of water is 15.7 and that the pKa of H3O+is -1.74. Both of the values are incorrect, and neither one is supported by experimental evidence. Yet the values persist because of the accepted wisdom that methanol is a stronger acid than water in dilute aqueous solutions. This presentation will describe the history behind the appearance of the erroneous values, describe the thermodynamically-correct derivation of the pKa of water, and show that calculation errors, misinterpretations, and poor referencing have led to the propagation of the erroneous values of 15.7 and -1.57 as the pKa of water and the pKa of H3O+, and to the erroneous belief that methanol is a stronger acid than water in aqueous solution. It will also describe the efforts that have gone into removing these errors from the literature. 

Bio: Tom Neils retired as a professor of chemistry after teaching for 25 years at Grand Rapids Community College. Before joining the faculty at GRCC, he was an associate professor at Wisconsin Lutheran College. He currently works as a science and math tutor for the TRIO program at GRCC, serves as a writer and presenter for the LibreTexts project out of UC-Davis, and occasionally is convinced to teach a chemistry course. He obtained a Bachelor’s of Science at Michigan Technological University and a Master’s and Ph.D. in Chemistry at Cornell University with Jim Burlitch, where he combined inorganic synthesis with EXAFS analysis of copper/zinc oxide catalysts. While at GRCC, Dr. Neils and his students participated in NSF-supported research collaborations with several chemistry faculty members at Hope College, and with Dr. Shannon Biros at GVSU. Dr. Neils also spent the Winter 2017 semester in the Biros lab as part of a sabbatical synthesizing gold (I) thiolates. He was given the GRCC Excellence in Education Award in 2014.