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ERIC Number: EJ1031401
Record Type: Journal
Publication Date: 2014-Feb
Pages: 7
Abstractor: As Provided
Reference Count: N/A
ISSN: ISSN-0021-9584
3-D Surface Visualization of pH Titration "Topos": Equivalence Point Cliffs, Dilution Ramps, and Buffer Plateaus
Smith, Garon C.; Hossain, Md Mainul; MacCarthy, Patrick
Journal of Chemical Education, v91 n2 p 225-231 Feb 2014
3-D topographic surfaces ("topos") can be generated to visualize how pH behaves during titration and dilution procedures. The surfaces are constructed by plotting computed pH values above a composition grid with volume of base added in one direction and overall system dilution on the other. What emerge are surface features that correspond to behavior in aqueous solutions. Equivalence point breaks become cliffs that pinch out with dilution. Buffer effects become plateaus. Dilution alone generates 45° ramps. Limitations of the Henderson-Hasselbalch equation can be seen by noting the conditions over which a plateau remains relatively flat. Because dissociation is driven by dilution, the surfaces demonstrate when the solution of a weak acid becomes indistinguishable from that of a strong acid. Surfaces are presented for hydrochloric acid, HCl (a strong acid); acetic acid, CH [subscript 3]COOH (a weak monoprotic acid); oxalic acid, HOOCCOOH (a weak diprotic acid) and l-histidine dihydrochloride, C[subscript 6]H[subscript 9]N[subscript 3]O[subscript 2]·2HCl (a weak triprotic acid). Supplementary materials include suggested use of topos in lecture, as worksheets and in support of laboratory activities for first-year college courses and third-year analytical chemistry courses. Also provided is pH TOPOS, the macro-enabled spreadsheets that quickly generate surfaces for any mono-, di-, or triprotic acid desired. Only a change of acid dissociation constants, K[subscript a] values, is required.
Division of Chemical Education, Inc and ACS Publications Division of the American Chemical Society. 1155 Sixteenth Street NW, Washington, DC 20036. Tel: 800-227-5558; Tel: 202-872-4600; e-mail:; Web site:
Publication Type: Journal Articles; Reports - Descriptive
Education Level: Higher Education; Postsecondary Education
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A