Titration Of Solution Research Articles

Experimental methods in chemical engineering: Karl Fischer titration

AbstractKarl Fischer titration (KF) measures the water content in organic and inorganic compounds. Water reacts with a titrant solution containing iodine and a sulphurous monoalkyl ester to produce a monoalkyl sulphate ester and HI. In volumetric titrators, a burette injects the titrant directly into a cell while coulometric titrators generate titrant in situ. Regardless of the volume of the sample, volumetric titration is limited to 100 mg, while coulometric titration is best suited for . KF is fast (), considered accurate (), and precise (). However, factors such as humidity, non‐standard analytes (hexane, isopropanol, ethylene glycol), tritrant composition, and temperature compromise its repeatability: the % sample standard deviation, (), varied from 2% to 60% (). This high variability is, in part, due to the experimental design that included samples and conditions ill‐suited for the technique. However, even for the tests for which KF is suitable, . Certain compounds react with the titrant, which increases the variability. The main sources of error affecting the analysis are ambient moisture, pH, solvent, sample handling, and titration speed. As of 2023, the Web of Science has indexed 1332 articles with Karl Fischer as a key word (Topic), but more than 3600 mentioning the technique (All fields). A bibliometric analysis classifies these contributions into five clusters: spectroscopy, stability, temperature, solubility, and mixtures.

Analysis of Basic Laboratory Skills of Science Education Students Using Pictorial-Based Instruments

Laboratory skills are an important aspect of natural sciences in schools and higher education, often linked to psychomotor aspects of learning. Several studies have developed several methods that can be used to evaluate laboratory skills, for example, the use of observation sheets equipped with rubrics. However, often using this method requires a longer learning time. Therefore, there is a need for research that examines how to evaluate students' basic laboratory skills. This research aims to analyze students' basic laboratory skills using pictorial-based instruments. This research method uses descriptive qualitative. This instrument is equipped with pictures that provide visualization. The basic laboratory skills are focused on experiments on making standard solutions from solids, making standard solutions from concentrated solutions, and acid-base titrations. Based on the analysis, it was found that the basic laboratory skills of science students in the experiment of making standard solutions from solids contained six basic skills, including selecting tools, weighing solids, transferring solids into a beaker, putting them in a volumetric flask, marking the solution, reading the meniscus mark. In the experiment of making a standard solution, there are five basic skills, namely selecting tools, taking the stock solution, transferring it into a volumetric flask, marking the solution, and reading the meniscus mark. The titration experiment consists of 8 skills, including selecting equipment, taking the analyte solution, taking the titrant solution, adding a titration indicator, using the titration technique, observing the endpoint of the titration, reading the meniscus, and calculating the solution's concentration.

Distance-based paper microfluidics as environmentally friendly platforms for monitoring acid-base titrations

The goal of green chemistry is to reduce the impact of chemical processes on the environment. In this context, it is important to develop new analytical tools that comply with the principles of green analytical chemistry (GAC) to contribute to the sustainable development of the planet. This study describes the development of an environmentally friendly methodology using paper-based analytical devices (µPADs) to perform acid-base titrations by distance-based measurements. The devices were composed of a circular zone defined with 5 mm diameter connected to a rectangular channel of 40 mm long × 3 mm wide. The titrations of acidic (strong and weak) and alkaline (strong and weak) solutions were successfully demonstrated using 10 µL of titrant solution and 10 µL of sample solution. The solution added into the zone travels different distances depending on the concentration of the titrated, thus promoting the channel coloration or discoloration. The distance measurements covered by the titrated solutions were obtained recorded with a digital caliper. As proof-of-concept for quantitative purposes, the µPAD was then used to determine the acetic acid content in commercial vinegar. The average distances ranged from to 32.0 to 32.5 mm and the concentration values ranged from 4.3 to 4.6% (m/v). Conventional acid-base volumetry was used as a control method, and the obtained results demonstrated no statistical difference at 95% confidence level. Lastly, the 12 principles of GAC were analyzed to evaluate the suitability of the proposed method. Considering a unified scale between 0 and 1, the final green value was 0.72. Titrations with distance-based detection on µPADs were found to be a technique with fast responses and low cost that can be used as a replacement for conventional practices in teaching laboratories or adapted for the detection of different analytes.

Method Measures Effective Scale-Inhibitor Concentration at Low Detection Limit

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 209503, “A Fast and Accurate Method for Scale-Inhibitor Effective Concentration Measurement With Low Detection Limit,” by Xin Wang, Rice University; Zhaoyi Dai, SPE, China University of Geosciences; and Saebom Ko, Rice University, et al. The paper has not been peer reviewed. _ The accurate measurement of residual scale-inhibitor concentration in produced brine is essential for scale prevention. However, these scale inhibitors are effective at substoichiometric concentrations in most production conditions. It is difficult to measure such low inhibitor concentration with traditional methods, especially for non- or low-phosphorous polymeric scale inhibitors. In the complete paper, an assay method is developed to determine effective scale-inhibitor concentration. The presented assay method is quick, robust, and accurate, with a relative error of less than 10% even at 1 mg/L of inhibitor. Experimental Setup and Methods Brine Chemistry Inhibitor (BCIn) Continuous-Stirred-Tank Reactor (CSTR) Method. The schematic of the BCIn CSTR testing apparatus is shown in Fig. 1. The original supersaturated solution (OSS) with a designated barite scale inhibitor is injected into the reaction vial with no head space. This OSS may contain zero or a certain amount of scale inhibitor, and it will be stirred continuously and kept at room temperature during the whole test period. At Time 0, the cation titrant solution (TC) and the anion titrant solution (TA) start to be pumped continuously into the reaction vial with the same flow rate by using two syringe pumps. A green laser beam (with a wavelength of 532 nm) is shone through the reaction vial; light intensity is recorded continuously as current by using a multimeter with a photodiode detector in real time. The time between Time 0 and the solution turbidity change, which is detected as current drop, is defined as the critical time. Without the supply of scale inhibitor from the TC and TA solutions, the inhibitor concentration in the reaction vial decreases exponentially and the inhibitor concentration at Time t can be calculated. With continuous dilution of the inhibitor and continuous supply of the barite supersaturated solution in the reaction vial by TC and TA solution, the small nuclei and crystals begin to accumulate in the reaction vial, resulting in a turbidity change detected by the laser at the critical time. Because of the exponential decrease of the scale inhibitors, it is observed that, with the same solution composition and residence time, critical time increases linearly with the initial concentration of inhibitor. A series of tests is designed to match the composition of target brine with different amounts of scale inhibitors. The standard curve can then be developed. For the brine with an unknown amount of scale inhibitor, the inhibitor concentration can be calculated from the measured critical time. The known-additions method also can be used to determine the unknown inhibitor concentration in a sample. This process, and its associated equations, is provided in the complete paper, as is sample pretreatment.

Silver Nanoplates for Colorimetric Determination of Xanthine in Human Plasma and in Fish Meat via Etching/Aggregation/Fusion Steps.

Silver nanoplates (AgP) were prepared and used in a colorimetric method for the evaluation of Xanthine (Xan) in blood plasma and fish meat. The detection mechanism for Xan was observed to occur via etching of AgP particles/aggregation/fusion steps, resulting in a color change from blue to grey. First, the basic Xan solution is adsorbed through partial substitution of capping molecules around the AgP with Xan, and then intermolecular hydrogen bonds form between AgP and AgP. Subsequently, the titrant Xan solution further etches the AgP and finally fuses particles together. Owing to the step by step mechanism, the response range towards Xan has two linear regression ranges: 0.15–0.60 μM and 0.61–3.00 μM, respectively. The detection limit in the range of 0.15–0.60 μM is 0.011 μM (S/N = 3). AgP exhibits good selectivity for Xan over other potential interferents such as amino acids and blood proteins. AgP achieves rapid detection of Xan and can be applied to the satisfactory determination of Xan in blood plasma and fish meat. This colorimetric sensor is easy to use, cost effective, fast, selective and user friendly.

Determination of Sodium Dodecyl Sulfate via Turbidimetric Titration with Poly(Diallyldimethylammonium Chloride)

AbstractTitration of sodium dodecyl sulfate (SDS) solution with poly(diallyldimethylammonium chloride) (PDDA) results in the formation of colloidal dispersion and gradual increase of turbidity. The titration end point can be determined in different ways, depending on both titrant concentration and optical detector used. The maximum value of turbidity depends on concentration of the titrant solution. An immersion probe is applicable to measure turbidity changes only at low concentrations of the colloidal dispersion. An external optical sensor is well suitable at both low and high concentrations of PDDA titrant. Near to the equimolar ratio of the analyte and titrant, large floccules are formed and turbidity values undergo chaotic fluctuations. Calibration graphs for SDS determination are straight lines. Determination range is from 0.2 to 40 mg L−1.

Modified potentiometric titration method to distinguish and quantify oxygenated functional groups on carbon materials by pKa and chemical reactivity

The presence and form of oxygenated functions on carbons lead to significant differences in material properties that impact surface chemistry, catalysis, electronic, and mechanical properties. Titration methodologies, specifically potentiometric and Boehm titrations, classify the types of acidic functions present on carbon materials into broad categories described as carboxylic, lactonic, and phenolic functions based upon the measured or estimated acid dissociation constants (pKa). The accuracy of these methods depends, however, on the estimates for pKa values and suffers when multiple possible species possess similar pKa values. Here, we improve upon past methods by combining potentiometric and chemical titrations, which involves identifying acidic functions by pKa values but also examining how functional groups react with alkaline titrants. Specifically, Brønsted acids like carboxylic and phenolic groups deprotonate reversibly when contacted with alkaline titrant solutions; however, lactonic functions undergo hydrolysis to form carboxylic acids and hydroxyls during identical treatments. Consequently, comparisons between sequential potentiometric titrations can be used to discriminate between functional groups by examining their pKa values but also their reactivity. Tests on probe compounds and functionalized carbon materials show our method successfully distinguishes lactones from other acidic functions on carbon surfaces and suggests the methodology complements other characterization techniques for carbon materials.

Open source, low-cost device for thermometric titration with non-contact temperature measurement

This work proposes a simple device for thermometric titration using a contactless sensor. A low-cost infrared sensor (around $5) was adapted in a disposable, polystyrene vessel for monitoring the temperature to determine the endpoint of neutralization, redox, and complexation titrations, using a homemade syringe pump to titration control. Open-source software was developed to control the device using the Raspberry Pi platform and to perform automatic endpoint determination. The influence of sample volume, the flow rate of titrant, and sensor distance from the solution were evaluated to lower the variation among measurements. The parameters chosen in this regard were 10 mL of sample, 0.8 mL min−1 of titrant solution flow rate, and 3 cm of distance from the sensor to the solution. Results for the determination of the acidity of sauces and the ascorbic acid and calcium content of pharmaceutical products were compared with those from official compendia. The performance of the sensor also was compared with an infrared camera. The proposed method agreed with conventional ones to an extent ranging from 93% to 106%. The robust analytical performance and low cost of the system are essential features that could broaden the use of enthalpimetric analysis in several laboratories.

Enhancing Biochemistry Lab with Arduino

The advancement of the new technologies of information and communication brought significant contributions to science education. The most remarkable and widespread technology is handheld computers, such as smartphones. Some examples of the benefits brought by personal computers to science education are the possibility of interaction with models and their development, the capacity of data storage, treatment, exchange, and visualization as well as the possibility to simulate complex systems. The capacity of having things (instruments, equipment, sensors, actuators) connected to the internet opened a unique perspective for science education that is the possibility of massively teaching science by doing science, even in online courses. Experiments can be planned, and data can be collected and interpreted remotely, using personal devices and equipment that can be made available to students for remote operation, from their schools.We have developed Arduino based pieces of equipment to enhance biochemistry lab optimizing data collection and treatment processes. In this work, it will be presented the results obtained from an online automatic titrator and a low‐cost spectrophotometer. The automatic online titrator (Figure 1) is composed of two scales on which stock solutions of titrants are deposited. The titrant solutions are added to the titrated using peristaltic pumps. A magnetic stirrer plate on which is placed a Becker containing the titrated, having its base illuminated for better visualization of the titration reactions. A pH meter is immersed into the titrated. All measurements of the sensors (scale and pH) are broadcasted online to a web page. The peristaltic pumps and magnetic stirrer controllers are also made online through the same page. Among the experiments that can be performed using this equipment is the amino acid, buffer, and pH indicators titrations.The low‐cost spectrophotometer (Figure 2) was constructed by using an RGB LED and a light detector. The RGB LED can be set to deliver visible light at various wavelengths. Among the experiments that can be performed with this equipment is the dosage of proteins and glucose. We used the low‐cost spectrophotometer for protein dosage by the Bradford method, and for glucose dosage by the Somogyi‐Nelsen method. The results obtained showed a correlation higher than 0.98 with the same measurement made in a commercial spectrophotometer.The use of Arduino technology has enormous potential to increase biochemistry laboratories. Among the equipment developed, the online automatic titrator allows the realization of titrations in a faster way and with the automatic registration of the data. It allows students to devote more time to the planning of the experiments and interpretation of the results. The spectrophotometer developed, presented results equivalent to commercial equipment, and for its small size and battery power, it can be used in field activities. We have also taught graduate students to build their equipment to optimise the experiments they perform in their research and classes.Support or Funding InformationThis study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001, CNPq, and grant# 2016/05243‐7, São Paulo Research Foundation (FAPESP)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Bioinspired Mineralization of Type I Collagen Fibrils with Apatite in Presence of Citrate and Europium Ions

Synthetic nanostructured hybrid composites based on collagen and nanocrystalline apatites are interesting materials for the generation of scaffolds for bone tissue engineering. In this work, mineralized collagen fibrils were prepared in the presence of citrate and Eu3+. Citrate is an indispensable and essential structural/functional component of bone. Eu3+ endows the mineralized fibrils of the necessary luminescent features to be potentially employed as a diagnostic tool in biomedical applications. The assembly and mineralization of collagen were performed by the neutralization method, which consists in adding dropwise a Ca(OH)2 solution to a H3PO4 solution containing the dispersed type I collagen until neutralization. In the absence of citrate, the resultant collagen fibrils were mineralized with nanocrystalline apatites. When citrate was added in the titrant solution in a Citrate/Ca molar ratio of 2 or 1, it acted as an inhibitor of the transformation of amorphous calcium phosphate (ACP) to nanocrystalline apatite. The addition of Eu3+ and citrate in the same titrant solution lead to the formation of Eu3+–doped citrate–coated ACP/collagen fibrils. Interestingly, the relative luminescent intensity and luminescence lifetime of this latter composite were superior to those of Eu3+–doped apatite/collagen prepared in absence of citrate. The cytocompatibility tests, evaluated by the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) colorimetric assay in a dose–dependent manner on GTL–16 human gastric carcinoma cells, on MG–63 human osteosarcoma cells and on the m17.ASC, a spontaneously immortalized mouse mesenchymal stem cell clone from subcutaneous adipose tissue, show that, in general, all samples are highly cytocompatible.

Microfluidic ballistic regime for the generation of linear gradients inside a capillary column: Proof-of-concept and application to the miniaturized acid-base volumetric titration

This work details a simple and original approach for the generation of linear gradients inside straight cylindrical microchannels such as a capillary column. The concept takes advantage of an oft-overlooked regime of dispersion of flowing liquids inside narrow channels: the ballistic regime. The ballistic regime is a pure convective regime and is produced by imposing a high velocity flow in a pre-filled capillary thus limited diffusion takes place. This is obtained by forcing the injection of a plug of solution on a short time scale t, much shorter than t<110×D/r2, D is the diffusion coefficient and r the capillary radius. The result is a stretched solution of a given length or depth of penetration, inside the capillary column. This leads to a linear mean concentration field through the mixing zone forming a linear gradient. In miniaturized systems, this transient regime is followed by mainly radial diffusion of the solution inside the capillary due to the short characteristic diffusion time of narrow channels. A convection-diffusion simulation was used to model the gradient formed under this ballistic regime. A specific experimental prototype set-up was designed to investigate this ballistic regime and the formation of a linear gradient of titrant NaOH solution inside a capillary tubing of 500 µm inner diameter and 35-cm total length pre-filled with nitric acid solution. With this prototype, the linear gradient was then pushed in a non-ballistic regime over a confocal fluorescence point detection system in order to measure the fluorescence emission of a fluorescent dye added to the solutions. Considering strong acid-base reaction, fluorescein was used due to its strong fluorescence dependency with pH near its pKa, i.e 6.4. A first set of experiments was realized to demonstrate the validity of such an approach and to determine the optimal condition for the formation of a linear gradient over 300 mm of the 350-mm capillary length. An injection pressure of 1000-mbars over 0.75 s was chosen. The first result was the stability of the system in its ability to produce reproducible linear gradients. As further proofs of feasibility, samples of different nitric acid concentrations were titrated with a 0.25 M NaOH solution. The result was rapid and reproducible titration curves obtained with a fully automated system that consumes less than approximately 70 µL of sample solution.

Towards Green Titration: Downscaling the Sequential Injection Analysis Lab-at-valve Titration System with the Stepwise Addition of a Titrant.

A downscaling in true titration based on a simple sequential injection analysis-lab-at-valve (SIA-LAV) has been proposed. A titrant solution was stepwise aspirated into a titration LAV chamber and a titration curve was obtained by monitoring the change in the solution color spectroscopically. This fully-automated SIA-LAV system required less volume of the sample/reagents, only a micro-liter scale, compared to the conventional method. The system was investigated with complexometric titration and acid-base titration. Application of the developed technique to some real samples has been demonstrated.

Uncertainty evaluation of alkalinity measurements on seawater samples

Alkalinity and pH are chemical parameters that, once measured in seawater, allow the calculation of the concentration of the carbonate system species CO32−, HCO3−, H2CO3 and CO2 which tend to be in equilibrium. Hence, these are key parameters used in oceanic carbon cycle models. The interpretation of the measured values depends on their respective uncertainties.This work presents a bottom-up evaluation of the uncertainty associated with measurements of total alkalinity, carbonate and bicarbonate concentrations in seawater samples by acid-base titration, with potentiometric detection, using as titrant a hydrochloric acid solution, 0.01 mol L−1 HCl in 0.67 mol L−1 NaCl, in order to approach working conditions to those of real seawater, with average ionic strength I = 0.67 mol L−1. The precision of the endpoint identification is estimated by the difference between the standard deviation of measurements repeatability and the combination of the repeatability of volumetric operations. Endpoint identification is the major uncertainty component that can be reduced by estimating alkalinity and concentration of the titrant solution, using a larger number of replicates. Total alkalinity was evaluated with a relative standard uncertainty of 1.5 % from triplicate measurements enabling distinction of relative differences larger than 6.3 % on a pair of seawater samples.A validated spreadsheet for estimating seawater alkalinity, carbonate and bicarbonate equivalent concentrations with respective uncertainty is made available as Electronic Supplementary Material.

Recovery of silver metallization from damaged silicon cells

Metallization is one of the key process steps to fabricate solar cells with high performance in a cost-effective way. Majority of photovoltaic solar cell manufacturing uses thick film screen print metallization with Ag containing paste to produce solar cells.The average lifetime of PV modules can be expected to be more than 25 years. The disposal of PV systems will become a problem in view of the continually increasing production of PV modules. These can be recycled for about the same cost as their disposal.The proposed method of acidic and basic etching of contacts, presented in this article can be successfully applied to broken solar cells from the landfill without a specialist analysis procedure. The amount of silver that can be recovered from the etching solution is up to 1.6kg/t of broken solar cells. The step-by-step procedure improves efficiency of silver recovery. The best and easiest method for general verification of the silver etching rate is classic titration with suitable concentrations of titrant solution.

Prediction of Edible-oil Iodine Values Based on Raman and near Infrared Spectroscopy

Based on Raman and near infrared spectroscopy (NIR), the modeling of edible-oil iodine value was conducted following chemometrics and support vector machine regression (SVR). The Raman and NIR spectral data of 44 oil samples were collected and preprocessed. The preprocessed spectral data at characteristic wavelengths were extracted with CARS and iPLS methods. Parameter optimization was performed following the grid search algorithm (GS), for the SVR iodine value prediction models. The results show that all the models built could predict the iodine values to some extent. An NIR-MSC-iPLS-SVR model exhibited the greatest stability and its correlation coefficient R of the prediction set reached 97.69%. The results show that NIR has more advantages in the fast prediction of iodine values and can be utilized to manufacture portable spectral instruments for edible-oil iodine-value determination. Vegetable oils can afford human body unsaturated fatty acids, vitamins, and other nutrients [1]. Wherein, the unsaturated fatty acids can ensure the physiological function of cells, reduce cholesterol contents, and perfect blood circulation [2]. The unsaturated fatty acid content can be indicated by unsaturation degree and iodine value (iodine number). The iodine value refers to the grams of iodine consumed in the addition reaction of 100 g of oil. The higher the iodine value is, the greater the unsaturation degree is, and the higher the unsaturated fatty acid content is. The iodine value determination methods include Wijs method (national standard), high-performance liquid chromatography (HPLC) method, and so forth [3-4]. Wherein, the Wijs method is precise and commonly used. Nevertheless, because the sample and titrant solution are immiscible, at the end point of titration, the color change is too slow. And, the method is tedious and requires a large amount of hazardous organic solvents [5-6]. Compared with the Wijs method, the spectral method is fast, efficient, and free of sample pretreatment. Hence, it has been increasingly used in oil and food industries [7]. Yu Yanbo et al. [8] used near infrared spectroscopy (NIR) technology to build a prediction model for the prediction of contents of 4 fatty acids in vegetable oils. María Á. Carmona et al. [9] identified oils and determined iodine values based on Raman spectroscopy.

Monitoring Acid–Base Titrations on Wax Printed Paper Microzones Using a Smartphone

This study describes the use of a smartphone for monitoring acid–base titrations on wax printed paper microzones. An array of twelve microzones of 5 mm diameter each was wax printed on filter paper. The analytical performance of the proposed devices was explored with acid–base titrations examples, where jaboticaba peel extract was used as a natural pH indicator. The color intensity was captured using a smartphone and analyzed through a free App named Photometrix®. Before titrations, color intensity versus pH was calibrated to be used as a reference in titrations as (i) strong acid versus strong base; (ii) strong base versus strong acid; and (iii) weak acid versus strong base. In all examples, images were obtained after the addition of each aliquot of titrant solutions. The obtained titration curves showed the same behavior as the conventional titration curves. After evaluating the feasibility of the proposed methodology, the concentration level of acetic acid was obtained in three vinegar samples. Although the obtained values ranged from 5% to 8% compared to the concentrations on the conventional method, the proposed methodology presented high analytical reliability. The calculated concentrations of acetic acid in three samples ranged from 3.87% to 3.93%, and the proposed methodology did not significantly differ from classic acid–base titration at a confidence level of 95%. The acid–base titration on paper-based devices is outstanding, since any titration can be completed within 5 min using 20 µL volumes. Besides, the use of a smartphone to capture images followed by analysis in a free app offers simplicity to all users. The proposed methodology arises as a new strand to be exploited in the diffusion of the analytical chemistry education field as well as an alternative for quantitative analysis with extremely simplified instrumentation.

Calorimetry of Nucleic Acids.

This unit describes the application of calorimetry to characterize the thermodynamics of nucleic acids, specifically, the two major calorimetric methodologies that are currently employed: differential scanning (DSC) and isothermal titration calorimetry (ITC). DSC is used to study thermally induced order-disorder transitions in nucleic acids. A DSC instrument measures, as a function of temperature (T), the excess heat capacity (C(p)(ex)) of a nucleic acid solution relative to the same amount of buffer solution. From a single curve of C(p)(ex) versus T, one can derive the following information: the transition enthalpy (ΔH), entropy (ΔS), free energy (ΔG), and heat capacity (ΔCp); the state of the transition (two-state versus multistate); and the average size of the molecule that melts as a single thermodynamic entity (e.g., the duplex). ITC is used to study the hybridization of nucleic acid molecules at constant temperature. In an ITC experiment, small aliquots of a titrant nucleic acid solution (strand 1) are added to an analyte nucleic acid solution (strand 2), and the released heat is monitored. ITC yields the stoichiometry of the association reaction (n), the enthalpy of association (ΔH), the equilibrium association constant (K), and thus the free energy of association (ΔG). Once ΔH and ΔG are known, ΔS can also be derived. Repetition of the ITC experiment at a number of different temperatures yields the ΔCp for the association reaction from the temperature dependence of ΔH.

Potentiometric Titration and Out-Of-Equilibrium pH Response of the Biotite-Water System

Minerals in soils contribute significantly to the capacity of soils to buffer pH disturbance. In this paper, we present the pH buffering capacity of a common soil phyllosilicate mineral, biotite. We performed equilibrium potentiometric titrations and we also monitored the pH response kinetics of the mineral-water system in order to develop an out-of-equilibrium model able to capture the interactions between minerals and the surrounding aqueous fluid. During titrations, after each addition of titrant solution from pH 11 to ca. 3, the pH response patterns were monitored over time until reaching a pseudo-equilibrium pH value. Based on the potentiometric dataset Best7, equilibrium calculations were performed to obtain the concentrations and the equilibrium protonation constants of each deprotonable component that fit best our titration curve. In parallel, the out-of-equilibrium pH responses over time at each point of the titration were used in a simple first-order kinetic approach that allow for the determination of “slow” proton exchange [H+ex]t0(mol L-1) and the associated rate constants for the exchange reactions, k (s-1). Our results show a maximum in “slow” proton exchange [H+ex]t0 associated to a minimal value of k at pH < 5 while at neutral and basic pH exhibits the opposite, i.e. , fast rate constant for a minimum value of the “slow” proton exchange. Expressing the observed “slow” proton exchange processes in terms of entropy production, our result demonstrate that the maximum resilience stability of biotite-water system to pH perturbation is in acidic pH, probably due to the consumption of proton associated with biotite dissolution reactions.

Unsaturated Heteropolyoxotungstates with Platinum Cation Complexation

Abstract Background: Polyanions are a special category of coordination compounds with a large development in last years. By coordination of metal oxoions at the lacunary polyoxometalates are obtained new compounds which are studied for theirs possible antitumoral and antiviral activities. The polyoxometalates can bind cations by oxygen atoms from their saturated surface structure or by embedding in vacant sites. Material and method: The methods used for determining cation coordination with the unsaturated polyoxotungstate are spectrophotometry and conductometry. The solutions used in this study were: for ligand a solution of K27[KAsW40O140] and for cation a solution of K2[PtCl6]. The variation of electrical conductivity of ionic species found in solution, caused by their concentrations, decreases during the complex formation, which was determined by conductometry. The spectrophotometric assay was performed to verify ratios between cation:ligand combination, determined by conductometry. Results: The graphical representations of conductivity function of number of moles of added titrant solutions emphasize that there are two types of coordination compounds with two different combination ratios ligand:cation at 1:2 or 1:4. The spectrophotometric determination performed, confirmed these ratios. Conclusions: There are two types of coordination complexes, and the ligand:cation ratios are well known for encrypting polyoxotungstates type used in the study. Besides the main active position SC where K+ alkaline cation is coordinated, it has four active stand side S1-4, which can coordinate metal cations, depending on the size of their cationic radius and the electronic charge they hold.

The constant composition method for crystallization of calcium carbonate at constant supersaturation

The exact control of supersaturation is of great importance when studying the formation of crystalline and amorphous matter. The constant composition method is suitable for the study of crystallization processes at constant supersaturation by controlled addition of titrants to a crystallizer to maintain constant pH. Not all aspects necessary for successful operation of this method are obvious from the existing literature, and the method is often used in an incorrect way. The focus of the present work is to highlight pitfalls associated with the constant composition method. The method is assessed and described in detail to show that even if the solution pH is kept constant, the supersaturation may change. First and foremost, it is illustrated how crucial it is to use a chemical composition of the titrant solutions which is in accordance with the initially prepared aqueous solution. General rules are presented for carbonates as to how the composition of the titrant solutions should be calculated based on total alkalinity in order to maintain constant supersaturation. This has – to the knowledge of the authors – not been shown before. Then, it is shown how exchange of carbon dioxide with the atmosphere corrupts the constancy of the supersaturation level during an experiment. Third, it is pointed out that the ionic strength should be kept constant throughout crystallization experiments since a change in ionic strength alters the activity of the ions in solution. Here, the determination of the thermodynamic driving force (supersaturation) is explained based on the relevant chemical equilibria, total alkalinity and calculation of the activity coefficients. The calculations are presented for the least stable polymorph of calcium carbonate, vaterite, but can easily be extended to the other polymorphs and other pH-dependent systems allowing for crystallization studies at low and maintained supersaturation levels typical of naturally occurring processes in geology and biomineralization, as well as formation of mineral scales in industry.