Chapter 1.2: Visualization of Buffer Capacity with 3-D Topos: Buffer Ridges, Equivalence Point Canyons and Dilution Ramps
Garon C. Smith, Mainul Hossain · The Mathematics Enthusiast · 2020
The BufCap TOPOS software generates 3-D topographic surfaces for acid-base equilibrium studies that portray pH and buffer capacity behavior during titration and dilution procedures. Topo surfaces are created by plotting computed pH and buffer capacity values above a composition grid with volume of NaOH as the x-axis and overall system dilution as the y-axis. What emerge are surface features that correspond to pH and buffer behaviors in aqueous solutions. Topo surfaces are created for pH, log buffer capacity and linear buffer capacity. Equivalence point breaks become pH cliffs and logarithmic buffer capacity canyons that grow shallower with dilution. Areas of high buffer capacity become rounded ridges. Dilution alone generates 45° ramps. Example systems include acetic acid, CH3COOH (a weak monoprotic acid); hydrochloric acid, HCl (a strong acid); oxalic acid, HOOCCOOH (a weak diprotic acid) and L-glutamic acid hydrochloride, C5H9NO4·HCl (a weak triprotic acid). The Supplementary files include a copy of the interactive BufCap TOPOS program as a downloadable Excel workbook. Its macro-enabled spreadsheets quickly generate surfaces for any mono-, di-, or triprotic acid. Only acid dissociation constants, Ka values, need be changed. Other materials include a PowerPoint lecture, materials/suggested laboratory activities for teaching with BufCap TOPOS, and derivation of new equations that permit the calculation of buffer capacities for titration/dilution composition grid points.