Document Detail

Acidity of frozen electrolyte solutions.
MedLine Citation:
PMID:  16610849     Owner:  NLM     Status:  MEDLINE    
Ice is selectively intolerant to impurities. A preponderance of implanted anions or cations generates electrical imbalances in ice grown from electrolyte solutions. Since the excess charges are ultimately neutralized via interfacial (H(+)/HO(-)) transport, the acidity of the unfrozen portion can change significantly and permanently. This insufficiently recognized phenomenon should critically affect rates and equilibria in frozen media. Here we report the effective (19)F NMR chemical shift of 3-fluorobenzoic acid as in situ probe of the acidity of extensively frozen electrolyte solutions. The sign and magnitude of the acidity changes associated with freezing are largely determined by specific ion combinations, but depend also on solute concentration and/or the extent of supercooling. NaCl solutions become more basic, those of (NH(4))(2)SO(4) or Na(2)SO(4) become more acidic, while solutions of the 2-(N-morpholino)ethanesulfonic acid zwitterion barely change their acidity upon freezing. We discuss how acidity scales based on solid-state NMR measurements could be used to assess the degree of ionization of weak acids and bases in frozen media.
Carmen Robinson; C S Boxe; M I Guzman; A J Colussi; M R Hoffmann
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  The journal of physical chemistry. B     Volume:  110     ISSN:  1520-6106     ISO Abbreviation:  J Phys Chem B     Publication Date:  2006 Apr 
Date Detail:
Created Date:  2006-04-13     Completed Date:  2007-07-25     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101157530     Medline TA:  J Phys Chem B     Country:  United States    
Other Details:
Languages:  eng     Pagination:  7613-6     Citation Subset:  IM    
W. M. Keck Laboratories, California Institute of Technology, Pasadena, CA 91125, USA.
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MeSH Terms
Electrolytes / chemistry*
Fluorine / chemistry
Hydrogen-Ion Concentration
Magnetic Resonance Spectroscopy
Reg. No./Substance:
0/Electrolytes; 0/Solutions; 7782-41-4/Fluorine

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