1,721,062 research outputs found
Salt bridges for minimization of liquid junction potentials in different solvent media
No full textSome recent applications of salt bridges for aq. and aq.-org. solvent mixts. are presented. The main cause of high residual liq. junction potentials, and of consequent intrinsic errors, in direct potentiometric electroanal. (pIon and pH measurements) is the inadequacy of the salt bridge selected for insertion in the operational cell. Salt bridges with RbCl, CsCl and KCl were compared. The decreasing order of equitransference in aq. solns. was RbCl, CsCl, KCl. The order was not kept in alc./water mixts. KCl improved its equitransference with increasing proportion of alc., while it was reverse for CsCl. The soly. of KCl sharply decreased with increasing alc. contents. NaCl, which had a poor equitransference in aq. solns., greatly improved its equitransference with increasing percentages of alc., and at ≈80% of alc. it behaved as good as CsCl
Sulfate-sensing electrodes. The lead-amalgam/lead-sulfate electrode
No full textA new, simplified design and a convenient prepn. procedure for the Pb(Hg)|PbSO4|SO42- electrode are proposed. This procedure ensures prepn. of stable amalgams and reproducible electrode potentials, which make this electrode useful and attractive for both thermodn. studies and electroanal. applications. For these purposes, the electrode prepd. according to the proposed procedure was exhaustively characterized both thermodynamically and as a sulfate-sensing electrode, in different sulfate solns., including H2SO4. Also, a practical standardization procedure is proposed. The Pb(Hg)|PbSO4|SO42- electrode can be structured with a built-in concd. Li2SO4 salt bridge for use as a sulfate-based ref. electrode. This electrode can be operated as a ref. electrode alternative to the conventional calomel or Ag|AgCl ref. electrodes in electroanal. practice
Recent advances in the electromotive force method for determining transference numbers of electrolytes and characterizing new salt bridges
No full textRecent transference-cell e.m.f. data sets for various 1:1 electrolytes in aqueous-organic solvent mixtures obtained in these laboratories for the determination of ionic transference numbers have been aggregated with earlier sets for 1:1 electrolytes in aqueous solutions and reexamined in the light of a new theoretical approach accounting for the solvent transfer phenomena accompanying ionic transfer. The potentialities and the precision of the transference-cell e.m.f. method have been highlighted, and new salt bridges, for use in aqueous-organic solvents, have been thereby characterized
Alternative reference electrodes
No full textTwo ref. electrodes, Hg(I) sulfate and Pb(I) sulfate, with incorporated Li2SO4 salt bridge, are proposed as alternatives for diffuse electrodes of calomel and silver chloride, in potentiometric monitoring such as pH-metry and pIonometry. With a Li2SO4 salt bridge of 2m, the operating potential of the two ref. electrodes is, resp., EREF[Hg4SO4] = 0.6326 ± 0.0008 V and EREF[PbSO4] = -0.3327 ± 0.0008 V, at 25°
Continuous conductometric determination of ionic impurities in hyperpure waters
No full textCombination of cond. and pH-transducer, makes it possible, in conjunction with a temp. sensor and an ad hoc programmed online minicomputer, to gain satisfactory information about nature and quantity of traces of foreign ions in highly deionized waters, so that the use of much more costly methods is often unnecessary
Reference value standards and primary standards for pH measurements in organic solvents and water + organic solvent mixtures of moderate to high permittivities
Full text linkRef. value stds. (pHRVS) and primary stds. (pHS) for pH measurements detd. prior to 1985, the aggregation of new stds. freshly detd. in the light of IUPAC rules and procedures, and the compilation of recommended data were reexamd. The pHRVS data (the RVS material is the 0.05 m K H phthalate buffer) now available cover the following solvents and/or their mixts. with H2O: MeOH, EtOH, 2-PrOH, 1,4-dioxane, MeCN, DMSO, and D2O. The various pHS now available cover MeOH, EtOH, DMSO and D2O
Multipurpose ammonium chloride : its possible use as a high-ionic-strength pH-metric standard
No full textPH measurements on high-ionic-strength sample solns., esp. at high acidities or high alkalinities, may be impaired by high residual liq.-junction potentials. To cope with this problem, a refined pH-metric procedures is suggested. It implies the use of CsCl salt bridges, (rather than KCl), together with the adoption of pH stds. having ionic strengths comparable with those of the sample solns., under conductimetric control. A scheme of detn. of high-ionic-strength pHs stds. based on aq. NH4Cl solns. of molalities 0,0534 < m < 7 is described
Characterization of potassium chloride as an equitransferent "intersolvental" salt bridge
No full textThe electromotive forces (emF) E-A and E-C of the following concentration cells with transference: Ag/AgCl/KCl(m(2))parallel to KCl (m(1))\AgCl\Ag and KxHg1-x\KCl (m(1))parallel to KCl (m(2))\KxHg1-x, respectively, together with the emfs E-MAX of the corresponding double cell without transference: KxHg1-xKCl (m(1))\AgCl\Ag-Ag\AgCl\KCl (m(2))\KxHg1-x have been measured at KCl molalities m (m(1) fixed and m(2) varied, with m(2) > m(1)) approximately up to the KCl solubility limit in 12 solvent mixtures for the three aqueous-oganic solvent systems (ethylene glycol + water),(acetonitrile + water), and (1,4-dioxane + water) up to 0.8 mass fraction of organic component. For all the cases explored, the E-A vs. E-MAX relation is linear over the whole KCI molality range. The ionic transference numbers tof KCI determined therefrom show a curvilinear dependence on the mass fraction of the organic component of the relevant solvent mixture and are found to fall in the range 0.52-0.48, viz, within +/-4% of exact equitransference (t(+) = t(-) = 0.5). In particular, KCI becomes exactly equitransferent (i.e., an ideal salt bridge) in aqueous mixtures with the following mass fractions of organic component: 0.4 ethylene glycol and 0.09 acetonitrile, as well as 0.12 methanol, and 0.08 and 0.34 ethanol from our recent work. Even if use of KCI as a salt bridge would be somewhat restricted by its limited solubility in high mass fractions of dioxane and acetonitrile and pending extension of investigation to other mixed-solvent systems, the above figures characterize KCI as a fairly good "intersolvental" salt bridge in electrochemistry, electroanalysis, and corrosion science
Thermodynamics of the amalgam cell {LixHg1-x | Li2SO4(m) | Hg2SO4 | Hg} in water, (methanol + water), and (acetonitrile + water) solvent mixtures
No full textThe emf. E of the amalgam cell {LixH1-x | Li2SO4(m) | Hg2SO4 | Hg} was measured as a function of the mole fraction x of Li metal in amalgams, and of the molality m of Li2SO4 in (methanol + water) and (acetonitrile + water) solvent mixts. contg. up to 0.3 mass fraction of the org. component, at the temp. 298.15 K. The resp. std. electromotive forces Emo were detd. together with the relevant activity coeffs. γ± as a function of Li2SO4 molality. A new scheme is introduced here and implemented for verification of the internal consistency of the γ± results in terms of complementary pairs of concn. cells with transference. The Emo depends linearly on the mass fraction w of the org. component of the solvent mixt. within the range explored, according to: Emo/V = 2.80137 - 0.20325w(methanol), Emo/V = 2.80137 - 0.23139w(acetonitrile), which reproduce the obsd. Emo values to within ±0.2mV
The transference numbers of aqueous hydrobromic acid
No full textThe transference nos. of aq. hydrobromic acid at molalities up to 7 mol kg-1 at 25° have been redetd. from the electromotive forces Et of the transference cell Pt|H2|HBr(m1)||HBr(m2)|H2|Pt, following the recently modified general treatment which implies a functional correlation between bromide ion transference no. tBR, water transference no. tw, and primary hydration no. h of hydrobromic acid
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