title: A pH Scale for the Protic Ionic Liquid Ethylammonium Nitrate.
abstract: To quantify the properties of protic ionic liquids (PILs) as acid-base reaction media, potentiometric titrations were carried out in a neat PIL, ethylammonium nitrate (EAN). A linear relationship was found between the 14 pKa  values of 12 compounds in EAN and in water. In other words, the pKa  value in EAN was found to be roughly one unit greater than that in water regardless of the charge and hydrophobicity of the compounds. It is possible that this could be explained by the stronger acidity of HNO3 in EAN than that of H3 O(+) in water and not by the difference in the solvation state of the ions. The pH value in EAN ranges from -1 to 9 on the pH scale based on the pH value in water.
authors.affiliation: Graduate School of Science and Engineering, Kagoshima University, 1-21-35, Korimoto, Kagoshima, 890-0065, Japan. kanzaki@sci.kagoshima-u.ac.jp.
authors.forename: Ryo
authors.initials: R
authors.lastname: Kanzaki
authors.affiliation: Graduate School of Science and Engineering, Kagoshima University, 1-21-35, Korimoto, Kagoshima, 890-0065, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Kodamatani
authors.affiliation: Graduate School of Science and Engineering, Kagoshima University, 1-21-35, Korimoto, Kagoshima, 890-0065, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Tomiyasu
authors.affiliation: Graduate School of Science and Technology, Niigata University, 8050, Ikarashi 2-no-cho, Nishi-ku, Niigata, 950-2181, Japan.
authors.forename: Hikari
authors.initials: H
authors.lastname: Watanabe
authors.affiliation: Graduate School of Science and Technology, Niigata University, 8050, Ikarashi 2-no-cho, Nishi-ku, Niigata, 950-2181, Japan. yumescc@chem.sc.niigata-u.ac.jp.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Umebayashi
keywords: acid-base catalysis; acidity; ionic liquids; pH scale; potentiometric titrations