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Commentary
Why Not Replace pH and pOH by Just One Real Acidity Grade, AG?
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Abstract
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 definition such as (i) pH of a neutral solution equals 7.0, a value which changes with temperature, and (ii) pH of an acidic solution will rise after dilution. The corresponding disadvantages hold good for pOH in alkaline solutions.
These disadvantages disappear after replacing pH and pOH by AG, the acidity grade: AG = log [H+]/[OH-]. AG of neutral solutions equals 0 at all temperatures, whereas AG of acidic solutions is positive and of alkaline solutions, negative. AG offers some other minor advantages as well.
Anybody using AG in calculations needs some knowledge of chemical equilibrium, in particular the reversible heterolytic dissociation of water. However, breaking with a long tradition appears to be the major obstacle to an introduction of AG.
Keywords (Audience):
High School / Introductory ChemistryKeywords (Domain):
CurriculumKeywords (Feature):
CommentaryKeywords (Subject):
Acids / BasesCiting Articles
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This article has been cited by 1 ACS Journal articles (1 most recent appear below).
Unified Approximations: A New Approach for Monoprotic Weak Acid-Base Equilibria
Harry L. Pardue , Ihab N. Odeh and Teweldemedhin M. TesfaiJournal of Chemical Education2004 81 (9), 1367Unified Approximations: A New Approach for Monoprotic Weak Acid-Base Equilibria
Harry L. Pardue , Ihab N. Odeh and Teweldemedhin M. TesfaiJournal of Chemical Education2004 81 (9), 1367This article describes a new approach to approximate calculations for monoprotic acid–base equilibria in otherwise pure water. The new approach, identified herein as unified approximations, uses a simple decision criterion to select between situations ...
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- Received: August 03, 2009
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