Log aH Research Articles

Determination of the Activity of Hydrogen Ions in Dilute Sulfuric Acids by Use of an Ionic Liquid Salt Bridge Sandwiched by Two Hydrogen Electrodes

The activities of hydrogen ions in 20-200 μmol dm(-3) H(2)SO(4) solution were estimated by use of an ionic liquid salt bridge (ILSB), made of tributyl(2-methoxyethyl)phosphonium bis(pentafluoroethanesulfonyl)amide (TBMOEPC(2)C(2)N), sandwiched by two hydrogen electrodes. The experimental pH values (pH = -log a(H), where a(H) is the activity of hydrogen ions) were in good agreement, within 0.01 pH unit, with those calculated using the Pitzer model. The difference between the experimental and theoretical pH values at 50 μmol dm(-3) H(2)SO(4) solution was much smaller than that obtained by use of a glass electrode in combination with a reference electrode with a concentrated KCl salt bridge. The source of the small deviation can be explained by the residual diffusion potential due to the dissolution of TBMOEPC(2)C(2)N in the H(2)SO(4) solution (W) and the resultant increase in the ionic strength of W. The use of a reference electrode equipped with an ILSB opens the way to accurately estimate the pH in dilute aqueous solutions, for which we have not had effective means.

PH Paradoxes: Demonstrating That It Is Not True That pH ≡ -log[H+

Six demonstrations highlighting paradoxes that arise if pH is incorrectly defined as -log[H+] are presented as justification for the recommendation that pH should be correctly defined as pH = -log aH+ in textbooks. For example, when acid with pH ~1 is diluted with an equal volume of 5 M MgCl2, one would expect the pH calculated as -log[H+] to increase as the concentration of acid is halved; surprisingly, it decreases to values below zero, as demonstrated with a pH meter or methyl green indicator. If a sample of the acid at pH ~2, and a second sample, diluted with salt solution so that it has pH ~0.5 are titrated with NaOH solution, equal volumes of base solution are required; but [H+] = antilog(-pH) is 0.01 in the first case and 0.32 in the second, leading to predictions of much different volumes of titrant. We could tolerate an approach to pH calculations that sacrificed reasonable practical answers for a sound theoretical foundation, but our current pedagogy seems to provide neither!

Examination of the time–water content superposition on the dynamic viscoelasticity of moistened polyamide 6 and epoxy

AbstractWe have investigated the behavior of moisture absorption by the polyamide 6 and epoxy samples in various humid environments at constant temperature and also examined the effect of absorbed moisture on their dynamic viscoelastic properties. The moisture absorption was revealed to show the Fickian type of diffusion and to shift the dynamic viscoelastic properties of the specimen to those at lower temperature, as an effect of plasticization. Anti‐plasticization taken with an increase in the storage modulus was also observed in a low‐temperature range below −50°C. The time–water content superposition was confirmed to hold at various equilibrium water contents at constant temperature for both polyamide 6 and epoxy. The relation of the shift factor, log aH, to the equilibrium water content for polyamide 6 has a form similar to WLF equation of time–temperature superposition, whereas the log aH for epoxy does not have such a form. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 560–567, 2004

Characterization of neoformed illite from hydrothermal experiments at 250 degrees C and P (sub v,soln) ; an HRTEM/ATEM study

Other| December 01, 1998 Characterization of neoformed illite from hydrothermal experiments at 250 degrees C and P (sub v,soln) ; an HRTEM/ATEM study Douglas M. Yates; Douglas M. Yates Washington State University, Department of Geology, Pullman, WA, United States Search for other works by this author on: GSW Google Scholar Philip E. Rosenberg Philip E. Rosenberg Search for other works by this author on: GSW Google Scholar Author and Article Information Douglas M. Yates Washington State University, Department of Geology, Pullman, WA, United States Philip E. Rosenberg Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online ISSN: 1945-3027 Print ISSN: 0003-004X GeoRef, Copyright 2004, American Geological Institute. American Mineralogist (1998) 83 (11-12_Part_1): 1199–1208. https://doi.org/10.2138/am-1998-11-1208 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Douglas M. Yates, Philip E. Rosenberg; Characterization of neoformed illite from hydrothermal experiments at 250 degrees C and P (sub v,soln) ; an HRTEM/ATEM study. American Mineralogist 1998;; 83 (11-12_Part_1): 1199–1208. doi: https://doi.org/10.2138/am-1998-11-1208 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Solid products from hydrothermal experiments conducted at 250 degrees C and P (sub v.soln) were characterized by powder X-ray diffraction (XRD) and ATEM/HRTEM. Experiments were conducted with muscovite, kaolinite, and quartz or amorphous silica in 2M KCl solutions for 43 to 176 d. Post-experiment solution compositions lie either within the illite (0.88 K) stability field or on the illite(0.88 K)-kaolinite or illite(0.88 K)-diaspore univariant boundaries in log (a K (super -) /a H (super -) ) vs. log aH 4 SiO 4 activity space. Transmission electron microscopy (TEM) observations of muscovite grain edges reveal the neoformation of illite crystals with a range of compositions (ATEM) from 0.31 to 0.89 K/O 10 (OH) 2 . The range of K-contents appears to narrow toward 0.88 K/O 10 (OH) 2 with increased experiment duration. HRTEM suggests the presence of 2 to 11 layer fundamental particles composed of illitic layers with 10 A periodicity. Fundamental particle thicknesses increase toward an average of 8 layers/particle with increased experiment duration. In the longer duration experiments, fundamental particle thicknesses were normally distributed about thicknesses of 4 and 8 layers, whereas fundamental particles with thicknesses <4 layers were common in a shorter duration experiment. The compositions and structure of the illites are consistent with the multiphase model, which states that the smectite-to-illite transition occurs through the step-wise formation of solubility-controlling phases consisting of fundamental particles with thicknesses of 1, 2, 4. and > or =8 layers. The increase in K-content and fundamental particle thickness with the extent of reaction suggests that the illite crystals underwent a prograde reaction culminating in the formation of end-member illite [0.88 K/O 10 (OH) 2 ]. This reaction, in conjunction with the previously observed, retrograde reaction from muscovite to end-member illite, demonstrates the stability of end-member illite in the system K 2 O-Al 2 O 3 -SiO 2 -H 2 O at 250 degrees C. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Experimental study of the solubilities of pyrite in NaCl-bearing aqueous solutions at 250–350°C

A total of sixty-three silica capsule experiments were performed to determine the solubilities of pyrite in NaCl-bearing aqueous solutions (0, 0.1, 0.5, 1, 2, 3, and 4 m) at 250, 300, and 350°C at pressures of vapor/liquid coexistence. The starting materials in the capsules were H 2 O(1) + FeS 2( s) + S ° ( s) ± NaCl ( s). After reaction times up to ~ 60 days, the quenched solutions were analyzed for ΣFe, σH 2 S, ΣSO 4 2−, and pH; the ΣFe content, ranging 5–1,300 ppm, generally increased with increasing temperature and ΣCl content of solution. The calculated solution compositions at the experimental P-T conditions fall mostly in the following ranges: pH = 2.0 to 3.2, log aH 2 s = −1.9 to −1.0, log aHSO 4 − = −3.8 to −2.0, and log aH 2( aq) = −7.0 to −5.0. Evaluation of the experimental data suggests that the various redox equilibria between solution and mineral were attained in most of the experimental solutions. The pH, a H 2 S( aq) , and a H 2( aq) of the solutions were controlled by the sulfur hydrolysis reaction (48° + 4 H 2 O( l) = 3 H 2 S( aq) + HSO 4 − + H +) and the sulfide/sulfate reaction ( H 2 S( aq) + 4 H 2 O( l) = 4 H 2( aq) + H + + HSO 4 −). The pyrite solubility is controlled by a general reaction: FeS 2( s) + nCl − + 2 H + + H 2( aq) = FeCl n 2− n + 2 H 2 S( aq). The equilibrium constants for this reaction, as well as those for association of ferrous chloride complexes ( Fe 2+ + nCl − = FeCl n 2− n ), were obtained at 250, 300, and 350°C; they were used also to compute the equilibrium constants for the reactions controlling the solubilities of pyrrhotite, magnetite, and hematite: FeS( s) + 2 H + + nCl − = FeCl n 2− n + H 2 S( aq); Fe 3 O 4( s) + 6 H + + 3 nCl − + H 2( aq) = 3 FeCl n 2− n + H 2 O( aq); Fe 2 O 3( s) + 4 H + + 2 nCl − + H 2( aq) = 2 FeCl n 2− n + 3 H 2 O( aq). Our experimental data suggest that the dominant Fe-Cl complex is FeCl + in solutions of ΣCl ≤ 0.5 m at 250°C and ΣCl ≤ 0.1 m at 300 and 350°C; FeCl 2 0 is dominant in solutions of the higher ΣCl contents at each temperature. The association constants for FeCl + and FeCl 2 estimated from this study are in good agreement with those estimated recently by Heinrich and Seward (1990), Ding and Seyfried (1992), Fein et al. (1992), and Palmer and Hyde (1992). Our solubility constants for pyrite are in good agreement with those obtained by Crerar et al. (1978) and Wood et al. (1987) for 3 m ΣCl solution at 350°C, but are 0.5–2 orders of magnitude higher than those obtained by them at lower temperatures and/or at lower ΣCl values. Our data suggest that natural hydrothermal fluids that are in equilibrium with pyrite, the most abundant sulfide mineral in the upper crust, are able to transport sufficient amounts (> 10 − m) of both Fe and H 2S to produce pyrite-rich ore deposits at temperatures above 250°C, and possibly at lower temperatures. The solubility of pyrite (and of other Fe-bearing minerals) is affected very little by a change of temperature, provided the pH, a H 2( aq) , a H 2 S( aq) , and ΣCl values remain constant.

Solubility of gold in NaCl-and H 2S-bearing aqueous solutions at 250–350°C

A total of 108 silica capsule experiments were performed in order to determine the solubility of gold in aqueous solutions containing both NaCl and H 2S at temperatures of 250, 300, and 350°C, at pressures dictated by vapor/liquid coexistence. The starting materials in the capsules were H 2 O + S° + gold wire + NaCl (0 to 4 m) ± Na 2 SO 4. The pH, a H 2 S ( aq), aH 2( aq), ƒ H 2(g) ,ƒ O 2(g) , and ƒ S 2(g) values of the solutions were controlled by the sulfur hydrolysis reaction (4 S ° + 4 H 2 O(1) = 3 H 2 S( aq) + HSO − 4 + H +) and the sulfide/sulfate reaction. The quenched run products were analyzed for Au (0.1 to 66 ppm), ΣH 2S, ΣSO 2− 4, and pH. The calculated solution compositions at 250–350°C fall in the following ranges: pH = 1.9 to 5.0, log aH 2 S( aq) = −2.0 to −0.7, log a HSO 4 − = −3.8 to −1.4 , and log a H 2( aq) = −7-0 to −4.7. The results of our experiments indicate that gold solubility is independent of the activity of Cl − and H + in the solutions, indicating that chloride complexes are not important. The gold solubility, however, increases with increasing H 2S(aq) activity, indicating that gold dissolved largely as a bisulfide complex according to the reaction: Au(s) + 2H 2S(aq) = HAu(HS) 0 2 + 1 2 H 2(aq) . The equilibrium constant determined from our experimental data for the above reaction is constant over a temperature range of 250 to 350°C at log K = −5.1 ± 0.3. The above equilibrium constant, together with that for a reaction involving Au(HS) − 2 obtained by Shenberger and Barnes (1989), determines the dissociation constant of HAu (HS) 0 2: HAu( HS) 0 2 = H + + Au( HS) − 2. The log K value becomes −5.3 ± 0.5 at 250°C, −5.6 ± 0.6 at 300°C, and −6.2 ± 0.6 at 350°C. Therefore, HAu(HS) 0 2 is the dominant gold-sulfide species at pH below about 5.5, while Au(HS) − 2 becomes dominant at higher pH conditions. The results from our study suggest that the solubility of gold in ore-forming fluids in equilibrium with pyrite and/or pyrrhotite at 250–350°C is typically between 0.1 ppb to 1 ppm Au, transported mostly as bisulfide complexes; gold-chloride complexes do not become important unless the fluid is H 2S-poor (e.g., <10 −4 m H 2S(aq) at 250°C), chloride-rich (>0.5 m 2Cl), and of low pH (<4.5). Precipitation of gold from ore-forming solutions may occur by increasing a H 2 ( aq), such as by reactions with organic matter or ferrous-bearing minerals, or by decreasing a H 2 S( aq), such as by precipitation of sulfide minerals or by mixing of H 2S-poor fluids. Simple cooling or heating of fluids without changing the H 2(aq) and H 2S(aq) contents is not an effective mechanism of gold precipitation when gold is transported largely as a bisulfide complex. Effects of oxidation or of boiling on gold precipitation, however, cannot be easily evaluated from the available thermodynamic data alone.

Which value for the first dissociation constant of carbonic acid should be used in biological work?

The apparent first dissociation constant of carbonic acid has been defined in different ways in the literature. Harned and co-workers (8-10) have defined it in terms of molalities of the participating species, including H ions: Ks = mHmHCO3/mCO2. In contrast, Hastings and Sendroy have defined an apparent constant in which acidity is expressed as H ion activity: K'1 = aHmHCO3/mCO2. These constants differ by a factor gamma H, the activity coefficient of H ions at the prevailing ionic strength. Therefore, pK'1 is greater than pKs by an amount equal to -log gamma H, which, at mu = 0.16 M, is approximately 0.1. It is important that the correct value for the apparent dissociation constant or its logarithmic form be entered in the mass action expression or in the Henderson-Hasselbalch equation in order to prevent significant errors in the computation by means of these equations of quantities that cannot be directly measured. Specifically, for the derivation of bicarbonate concentration from PCO2 and pH (-log aH), pK'1 is to be used and not an uncorrected pKs.

Solar abundance of praseodymium

16 lines of Pr ii possibly present in the solar photospheric spectrum have been studied. When including hyperfine structure in synthetic calculations, investigations of 9 lines result in an abundance APr = 0.71 ± 0.08 in the log AH = 12.00 scale.

Azidität konzentrierter elektrolytlösungen

The comparison of the conventional (electrochemically measured) pH-value with the pwH-values in concentrated salt solutions, as well as measurements in cells of the type Hg/Hg2Cl2(s)Cl−, MeA/Reference electrode show that in such solutions the pH can be considered to be approximately equal to log aH+. The influence of neutral salts upon the activity of the hydrogen ions in dilute strong acids is interpreted as being electrostatic in nature; this interpretation is in good agreement with the measured changes.The effect of the increased hydrogen ion activity (caused by neutral salts) upon equilibria involving H+ ions and upon the rate of (Particularly electrochemical) reactions is discussed.

A Study of the Determination of Solar Atmospheric Abundances

A study is made of the determination of solar atmospheric abundances from the observed intensities of faint Fraunhofer lines. The method of weighting functions, which utilizes the results of the observed limb-darkening, is considered in detail. An alternative method is proposed, the method of the Planckian gradient, which makes no recourse to limb-darkening observations and which is entirely dependent upon the physical characteristics of the solar atmospheric model considered. Throughout the paper reference is made to the case of nitrogen (ionization potential = 14.54 volts) primarily to compare results obtained by the above two methods. Nine absorption lines are considered and the nitrogen abundance is determined from each of the nine lines. Appreciable discrepancies are found between the results obtained by the two methods. Theoretical considerations lead to the conclusion that in the case of nitrogen, and in general for all elements of high ionization potential, the method of weighting functions is quite unreliable and the Planckian gradient method should be used. Three atmospheric models are considered, and, for nitrogen, the mean results obtained by the latter method are (on the basis log AH = 12.00) Claas model: log AN = 7.71, Vitense model: log AN = 7.81, Swihart model: log AN = 7.93 (cf. Hunaerts 9.02, Unsöld 8.61).