Prev. Article Next Article Table of Contents

Article

pKw Is Almost Never 14.0: Contribution from the Task Force on the General Chemistry Curriculum

Citing Articles

Your current credentials do not allow retrieval of the full text.

Purchase the full-text

PDF/HTML,
figures/images,
references and tables,
(where available)

Stephen J. Hawkes

Oregon State University, Corvallis, OR 97331-4003

J. Chem. Educ., 1995, 72 (9), p 799

DOI: 10.1021/ed072p799

Publication Date: September 1995

Abstract

The value of -log([H⁺][OH^-]) is not 14.00 at 25 ^oC in any circumstance where a student is likely to need it. If calculations are taught that use Kw then the correct value should be used, and should preferably be the Bronsted value aH⁺[OH^-]. Values of pK_w under both definitions, have been calculated from published data for various ionic strengths, temperatures, and pressures and tabulated. Calculations of pH are even then reliable only in the first decimal and approximate in the second. Texts deceive their readers when they quote 14.00 and give answers to two decimals. The value of such calculations in first year chemistry is questionable. Some suggestions are offered for teaching qualitative understanding of autoprotolysis. Plots of pK_w against temperature or against the ionic strength of the solution pass through a minimum. pK_w decreases with increasing pressure.

Keywords (Audience):

First-Year Undergraduate / General

Keywords (Feature):

Textbook Forum

Keywords (Pedagogy):

Misconceptions / Discrepant Events

Keywords (Subject):

Atomic Properties / Structure

View: Hi-Res PDF | PDF w/ Links

Citing Articles

Citation data is made available by participants in CrossRef's Cited-by Linking service. For a more comprehensive list of citations to this article, users are encouraged to perform a search in SciFinder.

This article has been cited by 6 ACS Journal articles (5 most recent appear below).

Polymeric, Metallic and Other Glasses in Introductory Chemistry
Stephen J. Hawkes
Journal of Chemical Education2008 85 (10), 1377
- Polymeric, Metallic and Other Glasses in Introductory Chemistry
  Stephen J. Hawkes
  Journal of Chemical Education2008 85 (10), 1377
  Polymeric, metallic, and other glasses and their importance are described suitably for introductory chemistry.
  Abstract | Hi-Res PDF | PDF w/ Links
pH Paradoxes: Demonstrating That It Is Not True That pH ≡ -log[H+]
Christopher G. McCarty and Ed Vitz
Journal of Chemical Education2006 83 (5), 752
- pH Paradoxes: Demonstrating That It Is Not True That pH ≡ -log[H+]
  Christopher G. McCarty and Ed Vitz
  Journal of Chemical Education2006 83 (5), 752
  Six demonstrations highlighting paradoxes that arise if pH is incorrectly defined as -log[H+] are presented as justification for the recommendation that pH should be correctly defined as pH = -log aH+ in textbooks. For example, when acid with pH ~1 is ...
  Abstract | Hi-Res PDF | PDF w/ Links
Complexation Calculations Are Worse Than Useless
Stephen J. Hawkes
Journal of Chemical Education1999 76 (8), 1099
- Complexation Calculations Are Worse Than Useless
  Stephen J. Hawkes
  Journal of Chemical Education1999 76 (8), 1099
  Calculations of complexation equilibria in introductory texts are unreliable to the point of absurdity. No case has been made that they should be taught, but if they are they should be taught using software that solves all the simultaneous equilibria and ...
  Abstract | Hi-Res PDF | PDF w/ Links
Why Not Replace pH and pOH by Just One Real Acidity Grade, AG?
Henk van Lubeck
Journal of Chemical Education1999 76 (7), 892
- Why Not Replace pH and pOH by Just One Real Acidity Grade, AG?
  Henk van Lubeck
  Journal of Chemical Education1999 76 (7), 892
  The definition of pH according to Sörensen (1909) as pH = -log [H+] offers some striking disadvantages to beginning students in a chemistry course, especially those with no knowledge of logarithms. They will face some puzzling consequences of this ...
  Abstract | Hi-Res PDF | PDF w/ Links
Thermodynamic Diagrams
Scot Chaston
Journal of Chemical Education1999 76 (2), 216
- Thermodynamic Diagrams
  Scot Chaston
  Journal of Chemical Education1999 76 (2), 216
  This article discusses examples of three thermodynamic diagrams that have been developed for this purpose. They are the thermodynamic energy account (TEA), the total entropy scale, and the thermodynamic scale diagrams. These diagrams help in the teaching ...
  Abstract | Hi-Res PDF | PDF w/ Links