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Titrimetric Analysis
Published in Pradyot Patnaik, Handbook of Environmental Analysis, 2017
One of the most common acid–base indicators is phenolphthalein. In an aqueous solution of pH less than 8, it is colorless. As the pH approaches 10, the color turns red. Some of the common acid–base indicators are listed in Table 6.2. An acid–base titration may be graphically represented by a titration curve, which is a plot between the change of pH versus the volume of acid or base added, causing such a pH change. Shapes of some of the titration curves are shown in Figures 6.1 through 6.3. Figure 6.1 illustrates the shape of a titration curve for a strong acid and strong base using the same concentrations of acid and base. Such a titration curve would have a long vertical section, typifying a strong acid–strong base titration. Near this vertical section, the addition of a very small amount of titrant causes a very rapid change in the pH. The midpoint of this vertical section is known as the equivalence point, which theoretically should be equal to the end point of the titration. The equivalence point in an acid–base titration involving equal concentrations of a strong acid and a strong base is 7. In other words, a strong acid would completely neutralize an equal volume of strong base of the same strength, or vice versa at pH 7. Figures 6.2 and 6.3 show the titration curves for acids and bases of different strengths. The vertical section is very short in the weak acid–weak base curve.
Titrations of Acids and Bases
Published in James F. Pankow, Aquatic Chemistry Concepts, 2018
Acidimetric titrations are usually carried out by adding volume increments of a relatively concentrated solution (titrant) of strong acid to the solution of interest. Similarly, alkalimetric titrations are usually carried out by adding volume increments of a relatively concentrated solution (titrant) of strong base. For both alkalimetric and acidimetric titrations, the titration curve is the plot of solution pH on the y-axis vs. amount (volume) of strong base or strong acid added on the x-axis.
Effect of sequentially adsorbed multilayers, citric acid(CA)-PEI-CA-PEI and PEI-CA-PEI-CA, on the surface chemistry and rheology of spherical α-alumina suspensions
Published in Journal of Dispersion Science and Technology, 2019
Wei Zhang, Yee-Kwong Leong, Chunbao Sun, Hong Fan, Xianwei Zhang
The pH of zero zeta potential pHξ = 0 was shifted to ∼4.5 by the adsorbed CA. At the initial pH of 11.8, no CA adsorption was expected as both the CA and α-Al2O3 are negatively charged. At both ends of titration curve, the zeta potential is −42.9 mV at pH 11.8 and 52.24 mV at pH 2.5. At pH 2.5, PEI at a concentration of 0.1 dwb% was added to form Layer 2. The pHξ = 0 was shifted to 10.2. The zeta potential of 58.7 mV at pH 2.5 was reduced progressively to −31.5 mV at pH 12, the end of the titration curve. Adsorption of PEI on CA is clearly evident from the change in zeta potential-pH behavior, in particular, the large shift in the pHξ = 0 from 4.5 to 10.2. Layer 3 CA shifted the pHξ = 0 marginally, to a lower pH of 10.1 and affected the magnitude of the positive zeta potential at any given pH only marginally. Similarly, Layer 4 PEI shifted pHξ = 0 to a slightly higher pH of 10.6 and increased the magnitude of the positive zeta potential slightly at most pH. The small changing of zeta potential values in layer3 and layer4 showed that CA and PEI adsorption are relatively weak in this two layers.
pH-responsive nanomicelles of poly(ethylene glycol)-poly(ε-caprolactone)-poly(L-histidine) for targeted drug delivery
Published in Journal of Biomaterials Science, Polymer Edition, 2020
Penghui Wang, Wei Liu, Shuai Liu, Rong Yang, Yajie Pu, Wenjie Zhang, Xiaoxue Wang, Xin Liu, Yanhan Ren, Bo Chi
The acid-base titration curve is shown in Figure 3(A), PEG block polymer solution has a good buffering capacity in pH 5.5–8.0. This shows that the nanomicelles have responsiveness in weak acidic of the tumor site, because the histidine imidazole based on unsaturated N atoms contains unpaired electron to lead to a pH sensitive property [18]. When pH of the environment turned into weak acid, unsaturated N amino of the poly (L-histidine) segment imidazole based become protons, Poly (L-histidine) chain segment transferred from hydrophobic to hydrophilic. These reactions allowed the micelles to swell, achieve the goal of drug release. From titration curve, the pKa value of polymer is about 6.8, which is consistent with the relevant literature report [42,44].
Synthesis, characterization and an application of graphene oxide nanopowder: methylene blue adsorption and comparison between experimental data and literature data
Published in Journal of Dispersion Science and Technology, 2021
Zeynep Ciğeroğlu, Aydın Haşimoğlu, Oğuz Kaan Özdemir
In the literature survey, the point of zero charge of the GO was estimated at in the range of 3.0–3.9 whose obtained from acid-base titration curve.[42–44] For better understanding of the effect of pH, it is necessary to know pKa (3.8) of MB.[45] Higher solution pH improves the adsorption capacity of MB. Electrostatic attractions can be occurred between the positively charged MB (pH > pKa) and the negatively charged GO (pH > pHpzc). Experimental results showed that optimal pH for MB adsorption on GO was 10. Adsorption mechanisms progress through hydrogen bonding and π–π interaction for pH ˂ pHpzc.[44]