D. Harvey - Modern Analytical Chemistry (794078), страница 103
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“An Alternative Procedure forTitration Curves of a Mixture of Acids of DifferentStrengths,” J. Chem. Educ. 1989, 66, 341.This short paper describes a modification to thetraditional Gran plot for determining the concentration of aweak acid in the presence of a strong acid.Clay, J. T.; Walters, E. A.; Brabson, G. D. “A Dibasic AcidTitration for the Physical Chemistry Laboratory,” J. Chem.Educ.
1995, 72, 665–667.Values for Ka1 and Ka2 for acids of the form H2A aredetermined from a least-squares analysis of data from apotentiometric titration.Crossno, S. K; Kalbus, L. H.; Kalbus, G. E. “Determinationsof Carbon Dioxide by Titration,” J. Chem. Educ. 1996, 73,175–176.Experiments are described for determining CO2 incarbonated beverages, NaHCO3 in Alka-Seltzer tablets, andthe molecular weight of CO2. Carbon dioxide is collected inNaOH and the concentrations of CO32– are determined bytitrating with a standard solution of HCl to thephenolphthalein and methyl orange end points.Flowers, P. A.
“Potentiometric Measurement of TransitionRanges and Titration Errors for Acid–Base Indicators,” J.Chem. Educ. 1997, 74, 846–847.Dilute solutions of nominally 0.001 M NaOH and HCl areused to demonstrate the effect of an indicator’s colortransition range on titration error. Potentiometric titrationcurves are measured, and the indicator’s color transitionrange is noted. Titration errors are calculated using thevolume of titrant needed to effect the first color change andfor a complete color change.Graham.
R. C.; DePew, S. “Determination of Ammonia inHousehold Cleaners,” J. Chem. Educ. 1983, 60, 765–766.A quantitative analysis for NH3 in several householdcleaning products is carried out by titrating with a standardsolution of HCl. The titration’s progress is followedthermometrically by monitoring the temperature of thetitration mixture as a function of the volume of added titrant.Household cleaning products may contain other basiccomponents, such as sodium citrate or sodium carbonate,that will also be titrated by HCl. By comparing titrationcurves for prepared samples of NH3 to titration curves for thesamples, it is possible to determine that portion of thethermometric titration curve due to the neutralization ofNH3.Kalbus, L.
H.; Petrucci, R. H.; Forman, J. E.; et al. “Titrationof Chromate–Dichromate Mixtures,” J. Chem. Educ. 1991,68, 677–678.A known amount of HCl in excess is added to a mixtureof CrO4– and Cr2O72–, with the HCl converting CrO42– toHCrO4–. The resulting solution is then back titrated with astandard solution of NaOH. The titration is followedpotentiometrically, showing two end points. Titration to thefirst end point provides a quantitative measure of the excessHCl, providing an indirect measure of the amount of CrO42–in the sample.
Titration to the second end point gives thetotal amount of Cr2O72– and CrO42– in the sample.Ophardt, C. E. “Acid Rain Analysis by Standard AdditionTitration,” J. Chem. Educ. 1985, 62, 257–258.This experiment describes a method for determining theacidity, reported as an equivalent molarity of H2SO4, of rainwater. Because the volume of standard base needed to titratea sample of rain water is small, the analysis is done by astandard addition. A 10.00-mL sample of nominally 0.005 MH2SO4 is diluted with 100.0 mL of distilled water andstandardized by titrating with 0.0100 M NaOH. A second10.00-mL sample of the sulfuric acid is mixed with 100.0 mLof rain water and titrated with the same solution of NaOH.The difference between the two equivalence point volumes—Continued1400-CH09 9/9/99 2:14 PM Page 359ExperimentsChapter 9 Titrimetric Methods of Analysisgives the volume of NaOH needed to neutralize the acidity inthe rain water.
Titration curves are measuredpotentiometrically and the equivalence point determinedfrom a Gran plot.Partanen, J. I.; Kärki, M. H. “Determination of theThermodynamic Dissociation Constant of a Weak Acid byPotentiometric Acid–Base Titration,” J. Chem. Educ. 1994,71, A120–A122.Directions are provided in this experiment fordetermining the dissociation constant for a weak acid.Potentiometric titration data are analyzed by a modifiedGran plot. The experiment is carried out at a variety of ionicstrengths and the thermodynamic dissociation constantdetermined by extrapolating to zero ionic strength.Thompson, R. Q.
“Identification of Weak Acids and Bases byTitration with Primary Standards,” J. Chem. Educ. 1988, 65,179–180.Potentiometric titration curves are used to determine themolecular weight and Ka or Kb for weak acid or weak baseanalytes. The analysis is accomplished using a nonlinear leastsquares fit to the potentiometric curve.
The appropriatemaster equation can be provided, or its derivation can be leftas a challenge.Tucker, S. A.; Acree, Jr., W. E. “A Student-Designed AnalyticalLaboratory Method,” J. Chem. Educ. 1994, 71, 71–74.359In this experiment the effect of a mixed aqueous–organicsolvent on the color transition range of common indicatorsis investigated. One goal of the experiment is to design anappropriate titrimetric method for analyzing sparinglysoluble acids and bases.Tucker, S. A.; Amszi, V. L.; Acree, Jr., W. E. “Studying AcidBase Equilibria in Two-Phase Solvent Media,” J. Chem. Educ.1993, 70, 80–82.This experiment shows how modifying the matrixof the solution containing the analyte can dramaticallyimprove the shape of the titration curve.Trialkylammonium salts, such as lidocainehydrochloride, are titrated in an aqueous solutioncontaining a surfactant. The presence of the surfactantincreases the trialkylammonium salt’s Ka, giving atitration curve with a more pronounced break.
Theeffect of adding an immiscible organic solvent, such asmethylene chloride or toluene, also is demonstrated.Werner, J. A.; Werner, T. C. “Multifunctional BaseUnknowns in the Introductory Analytical Chemistry Lab,”J. Chem. Educ. 1991, 68, 600–601.A potentiometric titration is used to determine if anunknown sample is pure Na2CO3, a mixture of Na2CO3 andNaHCO3, pure Na3PO4, or a mixture of Na3PO4 andNa2HPO4.Three experiments involving complexometric titrations are described in this second block of experiments.Fulton, R.; Ross, M.; Schroeder, K.
“SpectrophotometricTitration of a Mixture of Calcium and Magnesium,” J. Chem.Educ. 1986, 63, 721–723.In this experiment the concentrations of Ca2+ and Mg2+in aqueous solutions are determined by titrating with EDTA.The titration is followed spectrophotometrically bymeasuring the absorbance of a visual indicator. The effect ofchanging the indicator, the pH at which the titration iscarried out, and the relative concentrations of Ca2+ and Mg2+are also investigated.Novick, S. G.
“Complexometric Titration of Zinc,” J. Chem.Educ. 1997, 74, 1463.Most experiments involving EDTA as a titrant use Ca2+and Mg2+ as an analyte. This experiment describes aquantitative analysis for Zn2+<b>Текст обрезан, так как является слишком большим</b>.
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