ACID BASE CHEMISTRY

The experiment of this Lab aims to explore the pH value of some common substances, such as acids, bases, and neutral solutions and experimentally prove the buffering capacity of biological substances. Precisely, the lab involves comparison of PH changes in a potato and distilled water solution as opposed to distilled water by progressively adding an acidic solution (vinegar). This lab demonstrates important principles in acid base chemistry, including the meaning of pH, pOH, the dependence of concentrations of hydrogen (H+) and hydroxide (OH-) ions, and the way that buffers act to oppose changes in PH. Incorporation of potato as a liver alternative during the experiment explains that in biological tissues, natural buffers (such as organic acids, proteins, and phosphates) occur in them to ensure pH homeostasis, which is important in enabling life to withstand striking effects of acidic intake.

The pKa of bicarbonate ion adsorbed on the surface of Pt(111), HCO3 − (ads), in CO2saturated KClO4/HClO4 aqueous solutions has been determined by judicious application of a theoretical model originally proposed by Smith and White (Langmuir 1993, 9 (1), 1-3) to explain voltammetric features found for non-redox active alkyl chain monolayers bearing carboxylic moieties irreversibly bound to gold surfaces. The analysis herein presented relied on and coverages derived from in situ Fourier transform infrared spectroscopy measurements as a function of potential and pH reported by Martinez-Hincapie et al. (J. Phys. Chem. C 2016, 120 (29), 16191-16199), as input parameters, yielding a pKa for HCO3 − (ads) of ca. 2.6 ± 0.2. This value is significantly smaller than that of HCO3 − (aq) in bulk solutions, a phenomenon associated with the bonding of the species to the electrode surface, a factor that markedly modifies its acid base characteristics.

This study involved the development of a two-tier diagnostic instrument to assess Thai high school students' understanding of acid-base chemistry. The acid-base diagnostic test (ABDT) comprising 18 items was administered to 55 Grade 11 students in a science and mathematics programme during the second semester of the 2008 academic year. Analysis of students' responses from this study followed the methodology outlined by Çalik and Ayas. The research findings suggest that the ABDT, the multiple choice diagnostic instrument, enables researchers and teachers to classify students' understanding at different levels. Most students exhibited alternative conceptions for several concepts: acid-base theory, dissociation of strong acids or bases, and dissociation of weak acids/bases. Interestingly, one of the concepts that students appeared to find most difficult, and for which they exhibited the most alternative conceptions, was acid-base theory. Some alternative conceptions revealed in this study differ from earlier reports, such as the concept of electrolyte and non-electrolyte solutions as well as the concentration changes of H 3 O + and OH − in water. These research findings present valuable information for facilitating better understanding of acid-base chemistry by providing insight into the preventable and correctable alternative conceptions exhibited by students.

Fundamental properties such as cation exchange capacity (CEC), permanent charge, pH PZC , and metal uptake of a Zn-containing montmorillonite are modified, in a predictable manner, by a mild chemical treatment using acetate. Acetate treatment allows a controllable increase of the CEC of montmorillonite up to 180 mequiv/100 g. The CEC of the clay is increasing for decreasing Zn content, with a slope of Δ[Zn]/Δ[CEC] ≈-2. X-ray powder diffraction analysis shows that the lamellar structure of the clay remains unaltered by the acetate treatment, while XPS substantiates the removal of Zn. H + uptake data show that the intrinsic protonation pK values and concentration of the variable charge sites (SOH) are not modified by the acetate treatment. In contrast, the concentration of the permanent charge sites (X-) increased linearly with Zn removal by acetate, leading to a significant H + and Cd 2+ uptake enhancement. A physical model is suggested where acetate removes Zn ions strongly bound in the clay, and this in turn modulates the permanent charge and the CEC of the clay.

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2003 Agustín Jaime Castro Montoya / Manuel Herrera Solano / Pedro Alberto Quintana Hernández / Medardo Serna González POTENTIOMETRIC ANALYSIS OF A REACTION SYSTEM OF ORGANIC ACIDS Journal of the Mexican Chemical Society, julio-septiembre, año/vol. 47, número ...

2003 Agustín Jaime Castro Montoya / Manuel Herrera Solano / Pedro Alberto Quintana Hernández / Medardo Serna González POTENTIOMETRIC ANALYSIS OF A REACTION SYSTEM OF ORGANIC ACIDS Journal of the Mexican Chemical Society, julio-septiembre, año/vol. 47, número ...

Surface acidity of albite has been determined by potentiometric titration of water-washed and unwashed powders at 23.58C and pH range of 2-9.5. Using NH Cl as the background electrolyte the surface was titrated with HCl and NH OH in 4 4 both forward and backward directions. These titrants have the advantage of possessing the same acid-and base-radicals as those of the background electrolyte salt. Acidimetric forward titration of unwashed albite, which is also independent of q Ž dissociation of NH , shows that titration curves of various ionic strengths intersect at a pH near 3.93 point of zero salt 4

Ongoing acidification of the global ocean necessitates a solid understanding of how biogeochemical processes are driving proton cycling and observed pH changes in natural waters. The standard way of calculating the pH evolution of an aquatic system is to specify first how biogeochemical processes affect total alkalinity, followed by the solution of a nonlinear acid-base equilibrium equation system. This approach, however, does not explicitly reveal how individual biogeochemical processes contribute to the overall proton cycling in the system. Here, we provide an extension of the classical acid-base theory that explicitly quantifies the proton production/ consumption by a given process, showing that it can be calculated as the proton-cycling sensitivity times the rate of the biogeochemical process at hand. The proton-cycling sensitivity emerges as a central concept in acid-base chemistry of natural waters and can be further decomposed as the ratio of a stoichiometric coefficient for the proton over the buffer factor. The stoichiometric coefficient for the proton expresses how many moles of protons would be produced per mole of reaction if buffering was absent, and is obtained by bringing the reaction equation of the process into a specific form: the fractional reaction equation at ambient pH. The buffer factor quantifies how acid-base systems attenuate the proton production/consumption by biogeochemical processes, and is identified as the negative of the partial derivative of the total alkalinity with respect to the proton concentration. Applying this new concept to an acidification scenario for the future surface ocean, we illustrate its potential to analyze proton cycling in natural waters. Thereby we show that a reduced buffer factor due to anthropogenic carbon input makes the ocean more vulnerable to any process influencing the pH.

Sulfuric acid or sulphuric acid also called oil of vitriol or hydrogen sulfate is an en important strong dibasic acid uses for the production of fertilizer in the chemical plant industry and manufacture by the contact process. Oleum or fuming sulfuric acid is obtained by dissolving SO3 gases in concentrated sulfuric acid solution and always dilute the concentration en by slowly pouring water with stirring. Concentrated 98 percent of sulfuric acid uses as an effective en dehydrating or dissociation reagent with strong en oxidizing properties. Annual about 150 million tons production of sulphuric acids of the whole world leaves 250000-ton sulfur per year on our environment which is responsible for acid rain or snow in the earth’s atmosphere.

The need to have a measure of the strength of some substituted benzoic acids in ionic liquid solution led us to use the protonation equilibrium of sodium p-nitrophenolate as a probe reaction, which was studied by means of spectrophotometric titration at 298 K. In order to evaluate the importance of electronic effect of the substituents present on the aromatic ring, both electron-withdrawing and -donor substituents were taken into account. Furthermore, to have a measure of the importance of the steric effect of the substituents both para-and ortho-substituted benzoic acids were analyzed. The probe reaction was studied in two ionic liquids differing for the ability of the cation to give hydrogen bond and π-π interactions, namely [bm 2 im][NTf 2 ] and [bmpyrr][NTf 2 ]. Data collected show that benzoic acids are less dissociated in ionic liquid than in water solution. Furthermore, the equilibrium constant values seem to be significantly affected by both the nature of ionic liquid cation and the structure of the acid. In particular, the ortho-steric effect seems to operate differently in water and in the aromatic ionic liquid, determining in this solvent medium a particular behavior for orthosubstituted benzoic acids. (1) (a) See, for example: Caldwell, J. J.; Davies, T. G.; Donald, A.; Mc Hardy, T.; Rowlands, M. G.; Aherne, G. W.; Hunter, L. K.; Taylor, K.; Ruddle, R.; Raynaud, F. I.; Verdonk, M.; Workmann, P.; Garrett, M. D.; Collins, I. J. Med. Chem. 2008, 51, 2147-2157. (b) Kornhuber, J.; Tripal, P.; Reichel, M.; Terfloth, L.; Bleich, S.; Wiltfang, J.; Gulbins, E. J. Med. Chem. 2008, 51, 219-237. (c) Tosco, P.; Rolando, B.; Fruttero, R.; Henchoz, Y.; Martel, S.; Carrupt, P.-A.; Gasco, A. Helv. Chim. Acta 2008, 91, 468-482. (d) Opatrilova, R.; Jampilek, J.; Raich, I.; Kacerova, S.; Havlicek, J.; Pekarek, T.; Dohnal, J.; Csollei, J. Curr. Org. Chem. 2009, 13, 965-975. (e) Innocenti, A.; Pastorekova, S.; Pastorek, J.; Scozzafava, A.; Simone, G. D.; Supuran, C. T. von Coburg, Y.; Camelin, J.-C.; Ligneaux, X.; Rau, O.; Schubert-Zsilavecz, M.; Schwartz, J.-C.; Stark, H. Bioorg. Med. Chem. Lett. 2010, 20, 1581-1584. (h) Jiang, Y. L.; Gao, X.; Zhou, G.; Patel, A.; Javer, A. J. Org. Chem. 2010, 75, 324-333. (2) See, for example: (a) Castro, E. A.; Garcia, P.; Leandro, L.; Quesieh, N.; Rebolledo, A.; Santos, J. G. K€ onig, P.; Prat-Resina, X.; Yu, H.; Elstner, M.; Fruenheim, T.; Cui, Q. Monsier, N. S.; Scott, E. L.; Beeftink, H. H.; Sanders, J. P. M. Biochem. Eng. J. 2009, 43, 92-97. (g) Olenic, L.; Mihailescu, G.; Pruneanu, S.; Lupu, D.; Biris, A. R.; Margineanu, P.; Garabagiu, S.; Biris, A. S.

The equilibrium constants for ion pair formation of some pyridines have been evaluated by spectrophotometric titration with trifluoroacetic acid in different ionic liquids. The basicity order is the same in ionic liquids and in water. The substituent effect on the equilibrium constant has been discussed in terms of the Hammett equation. Pyridine basicity appears to be less sensitive to the substituent effect in ionic liquids than in water.

The equilibrium constants for ion pair formation of some pyridines have been evaluated by spectrophotometric titration with trifluoroacetic acid in different ionic liquids. The basicity order is the same in ionic liquids and in water. The substituent effect on the equilibrium constant has been discussed in terms of the Hammett equation. Pyridine basicity appears to be less sensitive to the substituent effect in ionic liquids than in water.

Os valores de acidez carboxílica (CA), fenólica (PhA) e total (TA) de um conjunto de cinco amostras padrão da Sociedade Internacional de Substâncias Húmicas (IHSS) e de quatro compostos modelo foram determinados pelo método de titulação potenciométrica. Os dados das curvas de titulação foram tratados pelo programa BEST7 assim como pela equação de Henderson-Hasselbalch modificada (MHHM) e os parâmetros obtidos mostraram-se extremamente dependentes do modelo matemático aplicado. Para as amostras de substâncias húmicas (SH), a aplicação da MHHM resultou em uma alta CA e uma baixa PhA, sendo o resultado praticamente oposto quando o programa BEST7 foi empregado. No caso dos compostos modelo entretanto, os valores de acidez convergiram aos valores esperados (teóricos) independente do modelo aplicado. Para investigar as razões das discrepâncias, variações na condução das titulações (p.e., titulação rápida ou lenta) também foram consideradas. O conjunto de informações mostrou que a determinação da acidez de SH por titulação potenciométrica é extremamente dependente do modelo matemático, assim como das condições experimentais aplicadas. Carboxylic (CA), phenolic (PhA) and total (TA) acidity contents of five International Humic Substances Society (IHSS) standards and four model compounds were determined via the potentiometric titration method. Titration curves were scrutinized both by the BEST7 algorithm and the modified Henderson-Hasselbalch model (MHHM). In the case of IHSS samples, the fitting data depended on the analytical procedure undertaken. Whilst high CA and low PhA were usually recorded using the MHHM, the opposite trend was observed employing the BEST7 algorithm. In contrast, in the case of model compounds the acidity values matched well with theoretical data regardless of the procedure. In order to better understand the reasons for such discrepancies changes in the titrations procedure (e.g.: fast or slow) were also considered. General data strongly suggest that acidity determination of humic substances (HS) by potentiometric methods is extremely dependent on both the choice of mathematical model to fit experimental data points as well as the experimental conditions employed.

Carboxylic (CA), phenolic (PhA) and total (TA) acidity contents of five International Humic Substances Society (IHSS) standards and four model compounds were determined via the potentiometric titration method. Titration curves were scrutinized both by the BEST7 algorithm and the modified Henderson-Hasselbalch model (MHHM). In the case of IHSS samples, the fitting data depended on the analytical procedure undertaken. Whilst high CA and low PhA were usually recorded using the MHHM, the opposite trend was observed employing the BEST7 algorithm. In contrast, in the case of model compounds the acidity values matched well with theoretical data regardless of the procedure. In order to better understand the reasons for such discrepancies changes in the titrations procedure (e.g.: fast or slow) were also considered. General data strongly suggest that acidity determination of humic substances (HS) by potentiometric methods is extremely dependent on both the choice of mathematical model to fit experimental data points as well as the experimental conditions employed.

The effect of a range of ionic liquids, with systematic variations in the cation and anion, on the rate constant of an aromatic substitution process was investigated. Temperature-dependent kinetic data allowed calculation of activation parameters for the process in each solvent. These data demonstrate a generalised ionic liquid effect, with an increase in rate constant observed in each ionic solvent, though the microscopic origins of the rate constant enhancement differ with the nature of the ionic liquid.

The equilibrium constants for ion pair formation of some pyridines have been evaluated by spectrophotometric titration with trifluoroacetic acid in different ionic liquids. The basicity order is the same in ionic liquids and in water. The substituent effect on the equilibrium constant has been discussed in terms of the Hammett equation. Pyridine basicity appears to be less sensitive to the substituent effect in ionic liquids than in water.

The quenching of the fluorescence of three anthropogenic fulvic acids (FA) provoked by Cu(II) (pH 6.0), Fe(III) (pH 4.0) and UO 2 2 + (pH 3.5), was analyzed by a non-linear method and by Stern-Volmer plots. The FA samples were extracted from composted sewage sludges (csFA), composted municipal wastes (mwFA) and composted livestock wastes (lsFA). Synchronous-scan fluorescence (SyF) spectra were collected as a function of metal ion concentration. Spectral data were treated by a self-modeling mixture analysis method (SIMPLISMA) to detect the SyF spectral band with the strongest quenching and to calculate the corresponding quenching profile. The analysis of these profiles by a non-linear method allowed the estimation of conditional stability constants (K) and of the percentage of non-complexing fluorophores. The same quantitative information was obtained by the modified Stern-Volmer equation taking into account the existence of fluorophores that do not participate in the complexation. Good agreement was found between the results of the two procedures. The log K calculated by the non-linear method were (standard deviation in parenthesis): csFA, Cu(II), 4.22 (5); Fe(III), 5.0 (1); UO 2 2 + , 5.2 (2); mwFA, Cu(II), 4.21 (3); Fe(III), 5.6 (2); UO 2 2 + , 4.7 (3); lsFA, Cu(II), 4.51 (8); Fe(III), 5.5 (2); UO 2 2 + , 3.6 (2).

The acid-base properties of two samples of anthropogenic fulvic acids (FA) extracted from the untreated sewage sludge (rsFA) of a municipal wastewater treatment plant and from the compost (csFA) obtained in the aerobical digestion of this sludge were studied. Potentiometric titrimetry, infrared spectroscopy and synchronous molecular fluorescence (SyF) spectroscopy were used to obtain experimental information about the acid-base properties of the samples. Moreover, the SyF spectral data which were collected as function of the pH were analysed by a self-modelling curve resolution technique, evolving factor analysis with a gradient concentration window (EFA-GCW), to calculate the number of acid-base systems, their SyF spectra and the corresponding distribution diagrams, from which the pKa values were estimated. Two acid-base systems with pKa values about 6.2 and 8.9 were detected for rsFA and three systems with pKa values about 3.8, 6.6 and 9.4 for csFA. The amounts of acid groups directly titrated in water were (standard deviations in brackets) about 6.8(1) for rsFA and 6.73(3) for csFA. This information for rsFA and csFA was compared with similar information for natural soil FA samples extracted from a pinewood soil. Beyond different structural composition, this comparison showed that the anthropogenic samples have a higher amount of acid structures, but the structures of natural samples have stronger acid properties.

The quenching of the fluorescence of three anthropogenic fulvic acids (FA) provoked by Cu(II) (pH 6.0), Fe(III) (pH 4.0) and UO 2 2 + (pH 3.5), was analyzed by a non-linear method and by Stern-Volmer plots. The FA samples were extracted from composted sewage sludges (csFA), composted municipal wastes (mwFA) and composted livestock wastes (lsFA). Synchronous-scan fluorescence (SyF) spectra were collected as a function of metal ion concentration. Spectral data were treated by a self-modeling mixture analysis method (SIMPLISMA) to detect the SyF spectral band with the strongest quenching and to calculate the corresponding quenching profile. The analysis of these profiles by a non-linear method allowed the estimation of conditional stability constants (K) and of the percentage of non-complexing fluorophores. The same quantitative information was obtained by the modified Stern-Volmer equation taking into account the existence of fluorophores that do not participate in the complexation. Good agreement was found between the results of the two procedures. The log K calculated by the non-linear method were (standard deviation in parenthesis): csFA, Cu(II), 4.22 (5); Fe(III), 5.0 (1); UO 2 2 + , 5.2 (2); mwFA, Cu(II), 4.21 (3); Fe(III), 5.6 (2); UO 2 2 + , 4.7 (3); lsFA, Cu(II), 4.51 (8); Fe(III), 5.5 (2); UO 2 2 + , 3.6 (2).