A PROPAGAÇÃO DO ERRO DO pKa DA ÁGUA NOS LIVROS DE QUÍMICA ORGÂNICA

Abstract

THE PROPAGATION OF THE ERROR IN THE pKa OF WATER IN ORGANIC CHEMISTRY TEXTBOOKS. In organic chemistry, the pKa is a property used to compare the acidity behavior for many substances, and to locate the position of equilibria in acid-base reactions and to provide information about structure and reactivity. Evidence in the literature shows that the values of pKa for water and hydronium ion, commonly cited in organic chemistry textbooks, are incorrect. The values of 15.74 for H2O and −1.74 for H3O+ are due to a propagated misconception in the equilibrium calculations while the correct values are 14.0 for H2O and 0.0 for H3O+. This subtle difference of 1.74 units on the pKa scale between both values reflects an error greater than 55 times in the level of acidity for these chemical species. An immediate correction of these values is necessary for the adequate teaching of organic chemistry. A literature search was conducted on the most used organic chemistry books in graduate and undergraduate courses in Brazil, revealing that almost all values cited were inadequate. The textbook Chemistry of Organic Compounds, 3rd edition (1965), by Carl Robert Noller is suggested as possible source of this misinformation in organic chemistry textbooks.