pKa Values in the Undergraduate Curriculum: What Is the Real pKa of Water?

Silverstein, Todd P.; Heller, Stephen T.

doi:10.1021/acs.jchemed.6b00623

Cited by 61 publications

(60 citation statements)

References 30 publications

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“…However, the pKa value for water was later shown to be 14 as predicted by thermodynamics. 35 By this comparison, pure methanol is predicted to be less acidic than water. Nevertheless, both 0.1 M NH 4 NO 3 electrolytes exhibit very similar pH conditions, namely 5.44 for water and 5.23 for methanol.…”

Section: Resultsmentioning

confidence: 99%

In situ electrochemical dissolution of platinum and gold in organic-based solvent

et al. 2018

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In situ highly sensitive potential-and time-resolved monitoring of polycrystalline gold and platinum electrochemical dissolution in pure organic media is reported. This was achieved by successfully upgrading electrochemical flow cell coupled to inductively coupled plasma mass spectrometry. Similar to the aqueous media, aggressive transient dissolution takes place during oxide formation and reduction. In contrary to the aqueous electrolyte, both gold and platinum exhibit enhanced anodic compared to the cathodic oxide-assisted dissolution in organic media. This study intends to highlight the capabilities of the new methodology, which will expand the studies of metals dissolution to the fields like organic electrocatalysis, corrosion, battery research, and sensors among others.

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Section: Resultsmentioning

confidence: 99%

In situ electrochemical dissolution of platinum and gold in organic-based solvent

et al. 2018

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“…[83][84][85][86] To further emphasize the degree of control over the O2 adsorption energies that is possible via this anion exchange approach, the equatorial bridging anions in MAF-Cl were exchanged with a wider range of species. Varying both the metal and bridging anion, we considered M = V 2+ −Ni 2+ and bridging ligands of (in order of increasing p a of the parent acid) 87,88 μ-Br -, μ-Cl -, μ-F -, μ-SH -, and μ-OH -. As shown in Figure 6, there is a qualitative trend in the O2 adsorption energy as a function of the bridging ligand, with stronger O2 binding found in MOFs that have more basic ligands.…”

Section: Overview Of Screening Results and Periodic Trendsmentioning

confidence: 99%

Tuning the Redox Activity of Metal−Organic Frameworks for Enhanced, Selective O2 Binding

Rosen¹,

Mian²,

İslamoğlu³

et al. 2019

Preprint

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Metal−organic frameworks (MOFs) with coordinatively unsaturated metal sites are appealing as adsorbent materials due to their tunable functionality and ability to selectively bind small molecules. Through the use of computational screening methods based on periodic density functional theory, we investigate O2 and N2 adsorption at the coordinatively unsaturated metal sites of several MOF families. A variety of design handles are identified that can be used to modify the redox activity of the metal centers, including changing the functionalization of the linkers (replacing oxido donors with sulfido donors), anion exchange of bridging ligands (considering μ-Br-, μ-Cl-, μ-F-, μ-SH-, or μ-OH- groups), and altering the formal oxidation state of the metal. As a result, we show that it is possible to tune the O2 affinity at the open metal sites of MOFs for applications involving the strong and/or selective binding of O2. In contrast with O2 adsorption, N2 adsorption at open metal sites is predicted to be relatively weak across the MOF dataset, with the exception of MOFs containing synthetically elusive V2+ open metal sites. As one example from the screening study, we predict that exchanging the μ-Cl- ligands of M2Cl2(BBTA) (H2BBTA = 1H,5H-benzo(1,2-d:4,5-d′)bistriazole) with μ-OH- groups would significantly enhance the strength of O2 adsorption at the open metal sites without a corresponding increase in the N2 affinity. Experimental investigation of Co2Cl2(BBTA) and Co2(OH)2(BBTA) confirms that the former exhibits only weak physisorption, whereas the latter is capable of chemisorbing O2 at room temperature. The chemisorption behavior is attributed to the greater electron-donating character of the μ-OH- ligands and the presence of H-bonding interactions between the μ-OH- bridging ligands and the O2 adsorbate.

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“…In terms of the proposed mechanism, the absence of spontaneous separation of GL is caused by the difficulty of glyceroxide formation in the presence of water. H 2 O is characterized by higher acid strength comparing with both glycerol and butanol, which is indicated by the thermodynamically correct value of pK a that is equal to 14.0 [14].…”

Section: T a B L E 3 Residual Potassium Content In Ester Layers Aftermentioning

confidence: 97%

“…In addition, the known numerical values of alcohols dissociation constants are applicable only to diluted water solutions; it is able to be useful for some estimation comparison of relative acidity of alcohols under the conditions of alkaline TE of oils. It is known that pK a (25 0 C) of methanol and glycerol is equal to 15.5 and 14.4, respectively [14]. n-Butyl alcohol, having three atoms on a longer carbon chain, reveals weaker acid properties as compared with methanol (pK a =16.1 [15]).…”

Section: T a B L E 3 Residual Potassium Content In Ester Layers Aftermentioning

confidence: 99%

Alkaline transesterification of sunflower oil triglycerides by butanol-1 over potassium hydroxide and alkoxides catalysts

2019

VKhKhT

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Butyl esters of fatty acids are used in engineering and are considered as potential biodiesel fuel. The difficulty of separation of products, obtaining by alkaline transesterification of oils, causes the pure attention of researchers to this one-stage of synthesis of butyl esters. The difficulty of separating the products obtained by alkaline transesterification of vegetable oils leads to the limited attention of researchers to this one-step route of the synthesis of butyl esters. The aim of this work was to compare the characteristics of the alkaline transesterification of sunflower oil on hydroxide and water-free alkoxide catalysts and to interpret the observed features from the point of view of reaction mechanism. Transesterification was carried out at the temperature of 20 and 40 0 C using potassium butoxide, methoxide and hydroxide. The highest equilibrium yield of butyl esters (up to 96%) was achieved when potassium butoxide was used, whereas it did not exceed 85% for the case of potassium hydroxide. The third order of reaction was determined. The reaction rate constants and apparent activation energies were calculated. The activation energies were found to be almost equal for both used alkoxides (30.5 kJ mol-1). The features of the formation of glycerol layer were studied; this layer appeared during transesterification using potassium butoxide. Alkaline solutions of catalysts in butanol were studied by IRspectroscopy. The degeneracy of valence vibrations of OH-groups in the region of about 3300 cm-1 was observed with as an increase in the potassium butoxide concentration. This may be due to the formation of associates of butanol and butoxide. The fundamental differences between reaction stages of methanolysis and butanolysis, caused by low dissociation degree of potassium butoxide in low polar butanol, were discussed. The ways of the formation of potassium glyceroxide and its role in the further course of the process were considered.

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pK_a Values in the Undergraduate Curriculum: What Is the Real pK_a of Water?

Cited by 61 publications

References 30 publications

In situ electrochemical dissolution of platinum and gold in organic-based solvent

In situ electrochemical dissolution of platinum and gold in organic-based solvent

Tuning the Redox Activity of Metal−Organic Frameworks for Enhanced, Selective O2 Binding

Alkaline transesterification of sunflower oil triglycerides by butanol-1 over potassium hydroxide and alkoxides catalysts

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