Ionization Constant Of Water Research Articles

Structure and acid-base properties of 1-propylimidazole-4,5-dicarboxylic acid

NMR spectra of 1-propylimidazole-4,5-dicarboxylic acid in DMSO- d 6 were studied. It was revealed that it presents in a zwitterion form in solution. The ionization constants in water were determined and their attribution to the certain sites was performed, at that for the deprotonation constants, the correctness of the attribution was confirmed by calculations. Based on the results of calculations, the preferred zwitterion and monoanion forms of 1-propylimidazole-4,5-dicarboxylic acid were selected from several alternative structures.

A Study of Indium Extraction with Carboxylic Acids with the Aim to Produce Scintillators for Solar Neutrino Detection by LENS Spectroscopy of Low-Energy Neutrino

The physicochemical properties of C4-C8 carboxylic acids (mutual solubility of carboxylic acids and water, ionization constants in water, distribution between water and 1,2,4-trimethylbenzene, dimerization constants in 1,2,4-trimethylbenzene) were studied. Since indium carboxylates are sparingly soluble in 1,2,4-trimethylbenzene and the second organic phase is formed in the system, In-containing scintillators can be prepared from C4-C5 acids only in the presence of neutral organophosphorus compounds. The best results were obtained with an extracting agent containing isovaleric acid (C5) and 0.25 M triisoamylphosphine oxide. The scintillator prepared in this system contained 80 g l−1 In and had a transparency of up to 2 m and a 40% light output. These parameters did not change when the sample was stored in tightly sealed dark glass vessels for 2 years at 12–34°C in an argon atmosphere. Acids C6-C8 can be used for In extraction without organophosphorus additives. The best results were obtained with methylvaleric acid (H2MVA, C6). The correlation between the transparency and light output of the scintillators, on the one hand, and the preparation conditions, on the other hand, was studied. The properties of scintillators prepared from solutions of polymeric indium hydroxy-2-methylvalerates in 1,2,4-trimethylbenzene { [In(2MVA)0.8(OH)2.2] n (n = 9–115)} were the best. A procedure for extracting indium hydroxycarboxylates and preparing scintillators suitable for LENS experiment was developed. Scintillators with a volume of 4 1, an In concentration of 50 g l−1, a light output more than 65%, and a 3-m transparency were prepared.

Chemical Speciation in the Copper (I)-Ammonia-Chloride System

Chemical speciation in the system CuI/NH3/Cl- which may be represented by the general equilibrium pCuI(aq)+qNH3(aq)+rCl-(aq)↔ Cup(NH3)qClr(p-r)+(aq) has been studied by glass electrode potentiometry at 25.0°C and an ionic strength of 1.00 M (NaClO4). A number of binary and ternary complexes were detected with formation constants, βpqr: logβ120 = 11.381�0.077, logβ111 = 8.920�0.045, logβ112 = 8.82�0.18 and logβ121 = 11.33�0.24. The ionization constant of water (pKw) and the protonation constant of ammonia (pKa) obtained by the same procedures were 13.7462�0.0012 and 9.4613�0.0010 at I = 1 (NaClO4), and 13.7165�0.0010 and 9.4521�0.0007 at I = 1 (NaCl) respectively.

Substituent Constants of Azulene

The ionization constants in water for six 3-substituted azuloic acids were determined spectrophotometrically. Conversion of these physical constants to their pKa values allowed a set of Hammett-type σ values for the substituents on these acids to be calculated. Determination of partition coefficients for nine 1-substituted azulenes allowed Hansch-type π values to be determined, using azulene as the model compound.

Deuterium isotope effects on the ionization of the lower carboxylic acids in water and deuterium oxide

To facilitate the interpretation of isotope effects on the ionization of weak acids in water and deuterium oxide, a comparison of these quantities with that for a standard acid is proposed. Therefore, a quantity Kr has been defined by the equation Kr = (kH/kD)/(kH′/KD′). The equilibrium constants KH and KD refer to the ionization constants in water and deuterium oxide respectively. The equilibrium constant KX′(X = H, D) refers to the acid used as a reference. An equation is derived from which it may be concluded, that for a series of acids closely similar in geometry and force field around the acidic group, a value of Kr close to unity should be obtained. To test this prediction the values of KH/KD for a series of n-alkanoic acids (N = 3–6) are compared experimentally with the value of KH/KD of acetic acid (25 °C). An emf method has been used in these measurements (quinhydrone electrode). In agreement with the theory a value for Kr close to unity has been observed.

Temperature dependence of point of zero charge of cobalt and nickel oxides and hydroxides

The points of zero charge (pzc) of well characterized Co(OH) 2, Co 3O 4, Ni(OH) 2, and NiO have been determined between 25 and 80°C. The pzc have been measured by three independent methods: (I) by finding the solution pH which does not change on addition of the oxide, (II) by electrometric titration of the oxide suspensions, and (III) by electrophoretic mobility (em) measurements. The pzc values differ with the extent of the equilibration. The em and the titration methods give similar pzc values but they are higher than the ones obtained for the primary equilibrium. The pzc values decrease with increasing temperature and this change is in the direction of the change of 1 2 p K w , the neutral point of water. For NiO and Co 3O 4, the value of (pzc − 1 2 p K w ) remains constant at all the temperatures studied and the magnitude of the change of pzc is explained by the change in the ionization constant of water, K w , with temperature. Similarly for Co(OH) 2 and Ni(OH) 2, the pzc values obtained from the titration method give a constant ( pzc − 1 2 pK w ) and the change is explained by the change of K w . However, the pzc derived from the primary equilibrium decreases more than the corresponding change in 1 2 p K w . Thus the potential on Ni(OH) 2 and Co(OH) 2 changes more than can be accounted for by the change in 1 2 p K w . The results are discussed with reference to the equation for the temperature dependence of pzc derived by Bérubé and De Bruyn.

Electronic spectra and structures of protonated pyrazine and quinoxaline N-oxides

The electronic spectra of neutral molecules and monocations of N-oxides of 2- and 3-substituted pyrazines and quinoxalines were measured, and their ionization constants in water were determined. The position of the protonation center in the investigated compounds was established.

Changes in electrical conductivity, ionization constant of water, and structuring at the absolute boiling point of water and aqueous solutions

Changes in electrical conductivity, ionization constant of water, and structuring at the absolute boiling point of water and aqueous solutions

The effect of pressure on the ionization of water at various temperatures from molal-volume data1

The apparent molal volumes of dilute (0.002 to 1.0m) aqueous HCl and NaOH solutions have been determined at 0, 25, and 50°C and NaCl solutions at 50°C. The partial molal volumes ( $$\bar V$$ ) of HCl, NaOH, and NaCl solutions have been determined from these apparent molal volumes and other reliable data from the literature. The partial-molal-volume changes ( $$\Delta \bar V_1 $$ ) for the ionization of water, H2O→H++OH−, have been determined from 0 to 50°C and 0 to 1m ionic strength from the partial molal volumes of HCl, NaOH, NaCl, and H2O. The partial molal compressibilities ( $$\bar K$$ for HCl, NaOH, NaCl, and H2O have been estimated from data in the literature and used to determine the partial molal compressibility changes ( $$\Delta \bar K_1 $$ ) for the ionization of water from 0 to 50°C and 0 to 1m ionic strength. The effect of pressure on the ionization constant of water has been estimated from partial-molal-volume and compressibility changes using the relation $$RTln(K^P /K) = - \Delta \bar V(P - 1) + \tfrac{1}{2}\Delta \bar K(P - 1)^2 $$ from 0 to 50°C and 0 to 2000 bars. The results agree very well with the directly measured values.

Temperature dependence of point of zero charge of alumina and magnetite

The points of zero charge (pzc) of alumina and magnetite suspensions have been determined between 25 and 90°C by measuring the distribution of the potential-determining ions (H +, OH −) at the oxide-solution interface as a function of pH. The pzc for both alumina and magnetite decreases with increasing temperature. The pzc of alumina decreases about 0.7 pH unit from 9.06 between 30 and 90°C. The change in 1 2 p Kw , the neutral point of water between the same temperatures is also 0.7 unit. It is also found that for alumina (pzc − 1 2 p Kw ) is constant (2.1 units) at all the temperatures studied. Thus the magnitude of the shift in pzc of alumina is explained by the change in the ionization constant of water K w, with temperature. However, for magnetite the variation of 1 2 p Kw with temperature does not fully account for the magnitude of the shift in pzc. The pzc decreases to 5.4 at 90°C from a value of 6.55 at 25°C, a decrease of 1.15 units for a corresponding decrease of only 0.79 units in 1 2 p Kw . Also the quantity ( 1 2 p Kw—pzc ) increases with increasing temperature (from 0.45 at 25°C to 0.8 at 90°C). These results do not seem to satisfy the equation for the temperature dependence of pzc derived by Berube and De Bruyn.

Blood gas relationships in the rainbow trout Salmo gairdneri.

ABSTRACT Oxygen dissociation curves were determined using blood from rainbow trout, acclimated for at least 3 weeks to temperatures of 6, 15 and 20 °C. Carbon dioxide tensions in the range 0·3–7 mmHg produced both the Bohr and Root effects in the blood. Increasing temperature, and hydrogen ions, whether raised individually or together, caused a decrease in blood O2 affinity (increased value for P50). Blood at low temperatures had a higher pH than blood at high temperatures. This is related to the fact that the ionization constant of water is diminished with decreasing temperature. When blood was 50 % saturated and was 1 mmHg, the pH value was 8·25 at 6 °C, 7·83 at 15 °C and 7·62 at 20 °C. The factors influencing unloading of oxygen from the blood are discussed. To release the same amount of oxygen from blood, a greater change in carbon dioxid tension is required at 6 °C than at higher temperatures. The Bohr effect expressed quantitatively (ΔlogP50/ΔpH) was –0·54 at 6°C, –0·57 at 15 °C and –0·59 at 20 °C. These values are similar to those for the blood of many mammals, and are within the range reported for fish, where whole blood has been used.

Pyridone–pyridol tautomerism in 2-hydroxypyridines with [5,6]-annelated rings and oxygen at the [6]-position: 2,3-dihydro-6-hydroxy-4-methylfuro[2,3-b]pyridine and 3,4-dihydro-7-hydroxy-5-methylpyrano-[2,3-b]pyridine

U.v. spectra in a range of solvents, i.r. and 1H n.m.r. spectra, and ionization constants in water have been determined for the title compounds (I) to (IV) and their O- and N-methylated derivatives (V) to (VIII). Replacement of the annelated five-membered ring by a six-membered one (a) reduces the ratio [pyridol]/[pyridone](KT) by a factor of ca. 15–30; (b) raises the base strength of the 2-methoxypyridine; (c) scarcely changes the base strength of the 2-pyridone; (d) lowers the acid strength of the 2-pyridone. The greater part of the ring-size effect on the tautomeric equilibrium is attributable to a Mills–Nixon–Brown type of ring strain, which is present in the five-membered ring in (II) but absent from the six-membered one in (IV); this strain is relieved by conversion into the pyridol (I), and by ionization; in part the ring-size effect is due to electron-withdrawal by the (strained) five-membered ring. In cation formation by the 2-pyridone (II) this electron-withdrawal and relief of ring strain oppose and almost cancel one another. 2-Hydroxy-6-methoxypyridine is intermediate between [(I). (II)] and [(III). (IV)] in both tautomeric equilibrium constants and ionization constants, but when allowance is made for the effect that a 4- and 5-alkyl group is expected to have in the first-named compound it is found that the properties of the pyrano-compound are quite similar to those of the ‘open-chain’ counterpart, whereas those of the furocompound are normally different. In the solid state all three above compounds exist in the pyridone form. Differences in zwitterionic character between the furopyridones and the pyranopyridones are shown not to be significant.In an Appendix attention is drawn to the relatively large errors in KT values derived by some common pK–KT relations.

Pyridone–pyridol tautomerism in 2-hydroxypyridines with [5,6]-annelated rings and carbon atoms at positions [5] and [6] : 1,3-dihydro-5-hydroxyfuro[3,4-b]pyridine, 1,3-dihydro-5-hydroxythieno[3,4-b]pyridine, and 1,3-dihydro-5-hydroxythieno[3,4-b]pyridine S,S-dioxide

U.v. spectra, in a range of solvents, i.r. spectra, and ionization constants in water have been determined for the title compounds (I) to (VI), their O- and N-methylated derivatives (VII) to (XII), counterparts that correspond to O- and S-ring fission products (XIII) to (XVI), and their methylated derivatives (XVII) to (XIX). All the the title compounds exist to an appreciable extent in the pyridol form in solution in dioxan. By a comparison of the cyclic sulphide with, on the one hand the cyclic sulphone, and on the other the cyclic ether, the effects of electron withdrawal and of ring strain have been assessed almost independently of one another. Replacement of the sulphide ring by the (smaller) ether ring (a) increases the ratio [pyridol]/[pyridone](KT) in dioxan by a factor of 2·7, (b) lowers the base strength of the 2-methoxypyridine, (c) lowers the base strength of the 2-pyridone, but by a much smaller amount, (d) raises the acid strength of the 2-pyridone. Replacement of the sulphide by the sulphone ring (a) produces a 2·8-fold increase in KT in dioxan, and (b), (c), and (d) reduces the base strengths and raises the acid strength, all by much greater amounts than in the above comparison. Analysis shows that no more than a third of the difference in KT between the cyclic ether and the cyclic sulphide is attributable to greater electron withdrawal (inherent plus ring-strain-induced) by the oxygen ring; about two thirds of it is due to a Mills–Nixon–Brown type of ring strain in the pyridone (II), which is relieved by conversion into the pyridol (I) or by ionization. The effects of ‘ring closure’ of the di-(methyl ether) to the cyclic ether, e.g. of [(XIII), (XIV)] to the [(I), (II)], show clear evidence of ring strain in the latter, whereas the effects of ‘ring closure’ of the dimethylthio-compounds to the cyclic sulphides indicate only a small amount of ring strain in the last-named. All the 2-hydroxypyridines listed are in the pyridone form in the solid state.

Chaleurs D'Interaction de Complexes par Liaison Hydrogène. II. — Complexes Phénol — Pyridine Substituée

AbstractEnthalpies of hydrogen bond formation between phenol and substituted pyridines are measured by calorimetry. The obtained energies are compared with the base ionization constants in water and the σ values of the pyridine substituents. The relation formation energy to infrared frequency shift is the same as for alcohols or phenols‐pyridine complexes. Distances between O and N atoms linked by the hydrogen bond are related to the infrared frequency shift: it is then concluded that a linear relation exists, for the complexes studied, between the heat of formation and the bond distance. Influence of steric hindrance on the bond distance is discussed.

Steric effects of o‐methyl groups on the ionization constants of phenols and anilines

AbstractThe values of the ionization constants of the phenols and anilines in water and water‐ethanol mixtures, determined by Gelsema et al.3, have been analysed for the presence of “o‐effects” by the method, devised by McDaniel and Brown7. It appeared that, contrary to the prevailing belief, in the phenol series an “o‐effect” is present, which is attributed to steric hindrance of hydration.The partition coefficients of benzene, toluene, the xylenes and the phenols and anilines derived from these hydrocarbons have been determined for the n‐heptane‐water system at 25°.Assuming that the standard free enthalpy of hydration, referred to the solution in n‐heptane, is in first approximation the sum of contributions of the hydrocarbon moiety and the ‐OH and ‐NH2 groups, respectively, the latter quantities (ΔG° ‐OH and ΔG° ‐NH2) have been calculated. An analysis for “o‐effects” showed them to be definitely present in the phenol series. In the aniline series the effect is so small that its significancy could not be proved.By combining the “o‐effect” on ΔG° ‐OH and ΔG° ‐NH2 (if real) with that on the ionization constants in water, the influence of steric hindrance of hydration by one o‐methyl group on the standard free enthalpy in aqueous solution could be calculated for the species R‐OH, R‐NH2, R‐O⊖ and R‐NH3⊕. The values obtained were 0.4, 0.1, 0.6 and 0.8 kcal/mole, respectively.Heinen's17 recent results on the association of phenols with acetone in carbon tetrachloride solution have also been explained in terms of steric hindrance of solvation by one o‐methyl group.

Chaleurs D'Interaction de Complexes par Liaison Hydrogène. 1. — Complexes Alcool ou Phénol — Pyridine

AbstractHeats of formation of Hydrogen bond complexes between pyridine and alcohols or substituted phenols are measured in carbon tetrachloride solution by calorimetry. The obtained energies are compared with the acid ionization constants in water and the a values of the phenol substituents. Steric hindrance lowers the bond energy. However the heats of complex formation are linearly related to the frequency shift of the hydroxyl absorption brought about by the Hydrogen bond interaction.

The ionization constant of water

Some textbooks claim that the ion product constant of water is constant under all conditions at a given temperature.

THE ACIDITY OF SOME AROMATIC FLUORO ALCOHOLS AND KETONES

A series of five trifluoroacetophenones and five phenyl trifluoromethyl carbinols have been synthesized and their ionization constants in water measured. They are the unsubstituted, p-methoxy, p-methyl, m-bromo, and m-nitro compounds. The ketones exist as hydrates in aqueous solution and each is about two pK units stronger than the corresponding alcohol. The acidities of both series are correlated by the Hammett relation with ρ values of 1.11 and 1.01 for the ketone hydrates and alcohols respectively. The acid strengths vary from a pKa of 9.18 for m-nitro-α,α,α-trifluoroacetophenone to 12.24 for p-methoxyphenyl trifluoromethyl carbinol.