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Coulometry
Published in Ernő Pungor, A Practical Guide to Instrumental Analysis, 2020
Coulometric analysis can be performed At a constant current (amperostatic or galvanostatic coulometry). In this case the measurement of the amount of electricity consists of the measurement of time. The equivalence point of the titration can be indicated by various methods such as photometric, potentiometric, or amperometric techniques.At a controlled potential (potentiostatic coulometry). In this case the potential of the working electrode is kept constant while the current decreases because of the decrease in the concentration of the reacting species. The amount of electricity is obtained by integrating the current vs. time function (Figure 4.1). In this technique, end-point detection is substituted by observing the decrease in the intensity. However, the residual current must be taken into account.
Ionic Equilibria in Aqueous Solutions
Published in Franco Battaglia, Thomas F. George, Understanding Molecules, 2018
Franco Battaglia, Thomas F. George
We need only to determine the equivalence point: a technique to accomplish this is to make use of acid–base indicators. We shall discuss them briefly in the next section. For the time being, let us move on and consider the titration of a weak base with a strong acid. As before, at the equivalence point the acid is completely salified, but being a weak acid, a salt of it gives hydrolysis, and at the equivalence point the pH is not neutral. For instance, if a solution of acetic acid has been titrated with lye, at the equivalence point we shall factually have a solution of sodium acetate, whose pH is alkaline; hence, the jump in pH at the equivalence point is less abrupt, but sufficient to allow the determination of the equivalence point with an indicator, as we shall see.
Chemical Equilibrium for Acids and Bases
Published in Paul Mac Berthouex, Linfield C. Brown, Chemical Processes for Pollution Prevention and Control, 2017
Paul Mac Berthouex, Linfield C. Brown
Figure 7.3 is the titration curve for an acid that is neutralized by the addition of a base chemical. The equivalence point in a titration is the point at which all the acid (or base) molecules in the solution react with an exact stoichiometric amount of the titrant. The pH is equal to 7 at the equivalence point only if a strong acid is used to titrate a strong base (or vice versa). If a strong acid is used to titrate a weak base, the equivalence point will be at a pH lower than 7 because of hydrolysis. For a strong base titrating a weak acid, the equivalence point will be at a pH higher than 7.
Automated system for performing pH-based titrations
Published in Instrumentation Science & Technology, 2023
Naga P. D. Boppana, Robyn A. Snow, Paul S. Simone, Gary L. Emmert, Michael A. Brown
A schematic of the decision tree for the automated potentiometric pH titration is presented in Figure 4. To begin a potentiometric titration, the analyst selects a pH-based titration method in the drop-down menu shown in Figure 2. The auto-titrator system reads and saves the initial pH of the sample. If the titration is set to a fixed equivalence point, the end-pH (pH where titration is stopped) is set to a user-defined input value. For example, the end-pH in alkalinity titrations is typically set to 4.3. While in a full-scale titration, the end-pH is set to either 2 or 12 depending on the analyte. The titrator then compares the initial pH of the sample to the end-pH. If the initial pH is equal to the end-pH, the titration is stopped without adding any titrant and reset for the next titration. Otherwise, the titrator adds a relatively large volume of titrant called a pre-dose to expedite the titration. The pH stabilization factor is the rate of change in pH at which the titrator waits until stabilization is less than or equal to 0.0025. This value was experimentally determined and may be modified.
Ion Exchange of Layered α- Zirconium Phosphates and Functionalized Derivatives: Determination of Thickness and Percent Functionalization by Exchange
Published in Solvent Extraction and Ion Exchange, 2020
Edward J. Broker Jr., Eduardo Cruz Jr., Brian M. Mosby
The ion-exchange behavior of the prepared zirconium phosphates was initially investigated by titration with sodium hydroxide (Figure 1). The ZrP nanoparticles display a continuous rise in the pH as sodium hydroxide is added. Exchange curves of more crystalline reflux materials typically contain plateaus during exchange and vertical regions once a pure phase has been obtained. The lack of plateaus and the ambiguity of the first equivalence point is indicative of solid-solution formation as opposed to conversion of the hydrogen phase directly to the sodium phase. This behavior is typical of particles with low crystallinity, where the irregularity of the cavities leads to increases in the solid solution ranges.[7] The final equivalence point of the titration occurs at ~6.6 milliequivalents of hydroxide per gram of ZrP (meq/g), which corresponds with the theoretical value based on the stoichiometry of the compound. Overall, the exchange behavior closely resembles that of the previously reported 2.5:48 samples.[8] This is expected, as the preparation of ZrP nanoparticles requires a final acid concentration of 3 M and 48-h reflux. The ZrP nanoparticles are slightly more crystalline than the reported samples, as indicated by the steeper slope of 2.5:48 corresponding to more solid-solution ranges.
Extraction of Uranium(VI) and Plutonium(IV) with Tetra-Alkylcarbamides
Published in Solvent Extraction and Ion Exchange, 2019
Clémence Berger, Cécile Marie, Dominique Guillaumont, Elisabeth Zekri, Laurence Berthon
The diluent used is hydrogenated tetrapropylene (TPH) and was purchased from Novasep. Nitric acid (analytical grade) was furnished by VWR Co. TBU was purchased from FluoroChem and the purity was checked by GC-MS (purity ≥98%). THU and TOU were obtained from ChemCollect and the purity was checked by GC-MS (purity ≥98%). MDEHA was synthesized by Diverchim CDMO company (purity by GC-FID >99%). TPU was synthesized in our laboratories using the procedure described below and the purity was checked by GC-MS (99.6%). The amide concentration in organic solutions was measured by potentiometric titration with perchloric acid (CHClO4 = 0.1 mol•L−1) in acetic anhydride.[25,26] This titration experiment was also used to evaluate the relative basicity of each extractant by determination of the pH at half-equivalence point with parallel tangents method.