Theoretical treatment of the spectrophotometric titration of bivalent cations with complexon-iii and metal-specific indicators

It was derived theoretically that a sharp end-point of this spectrophotometrical titration is defined, in order of importance, by: 1. *K_C ? *K_I (numerically speaking, log$\text{*K}{}_{\mathrm{C}}\text{*K}{}_{\mathrm{I}}$ should be at least 4); 2. *K_I being large (numerically e.g. 10⁴-10⁵); this is already reached by choosing a high pH; 3. it being low; 4. m_t being as high as possible.     

Amperometric argentimetric and mercurimetric titration of sulfhydryl: Mercurimetric titration

The ampero-mercurimetric titration of cysteine (RSH), glutathione (GSH), thioglycolic acid (TSH) and 2-mercaptoethanol (ESH) at the RMPE at pH 9 yields a sharply defined end-point corresponding to the composition (XS)₂Hg. Under the same conditions with the KPtWK two lirciiks an; (ibst'rvc-d in the titration lines with RSH and GSH, corresponding to compositions (RS)₂Hg and (RS)₂Hg₂ respectively. On the other hand, with TSHl and ESH only one clear break is found at the RPtWE corresponding to ('l'S)₂Hg or (ES)₂Hg Conditions liave been describcd for the accurate mercurimetric titration of the thiol compnunds at pH 2 in the pesence of 0.01 M sulfur dioxide at the RMPE, use of this can be made in the determination of disufides and in the determination of the equilibrium concentrations of the reaction betwcen a disulfide and a sulfite at varying pH.     

Integrated absorption intensities of haloethanes and halopropanes

The infrared absorption intensities of the chlorofluorocarbons C₂Cl_xF_y, (x + y = 6); the hydrofluorocarbons C₂H_xF_yH (x + y = 6); and a number of hydrochlorofluorocarbons, including some members of the propane series, have been measured. Absorption intensities have been obtained by integration over specified ranges of frequencies. The ranges used include the atmospheric window (1250t-833 cm⁻¹), 3500-450 cm⁻¹, 1300-700 cm⁻¹, and those for selected individual absorption bands. Comparisons of the results have been made with published work where available, and attention is drawn to possible sources of error in the measurement of band areas. The spectra of the halopropanes have been included for the range 3500-150 cm⁻¹. A preliminary study has been made of the relation between the number of fluorine atoms in the molecule and the intensity of absorption of the CF stretching vibrations.     

Azeotropic line determination from the caloric data on binary stratifying systems

The experimental isochoric heat capacity values of stratifying n-hexane-water mixtures of the compositions 0.120, 0.166, 0.200, and 0.256 H₂O mole fractions were obtained using a high-temperature adiabatic calorimeter over the density ranges 244.74–498.25, 121.06–438.21, 252.02–500.00, and 208.11–398.88 kg/m³, respectively. The C _{V, x} heat capacities were tabulated for the mixture with 0.120 H₂O mole fractions. Liquid-liquid and liquid-gas phase equilibrium curves were plotted. The suggestion was made that the intersection point between these curves characterized the state of an azeotrope. The azeotropic line with the critical point at its end was constructed.     

The accuracy and precision of the classical technique for locating the point of maximum slope on a potentiometric titration curve

When it is applied to data simulating those that might be obtained in the titration of either a strong acid or a monobasic weak acid with a strong base at the same concentration, the classical-technique for locating the end-point of a potentiometric titration has a bias that is statistically indistinguishable from zero. Its precision depends on the standard error of measurement of the volume of reagent but exhibits no detectable dependence on the standard error of measurement of the pH. If the acid is strong, the precision is improved by decreasing its concentration; if the acid a weak, the precision is improved by inccreasing its pK_a value or by decreasing its concentration.     

Oxidations with alkaline permanganate using monovalent thallium for the back titration: Estimation of lead. selenium,tellurium and chromium

Monovalent-thallium can be successfully used for the back titration of KMnO₄ in the course of estimating Pb⁺², Sc⁺⁴, Te⁺⁴ and Cr⁺³.Reduction of KMnO4 with Tl+ in alkaline solution yields MnO₄^-2 which then passes to MnO₂. he end-points are attained late, but in presence of telluric acid the end-point at MnO₂ stage corresonds to the theoretical value. Reduction at the MnO₄^-2 stage can be checked in presence of Ba⁺² ns and good results obtained with 1–1.5N NaOH.     

End-point evaluation in instrumental titrimetry-I Linear extrapolation of hyperbolic titration curves

A method is described for the estimation of a systematic titration error which is introduced by linear extrapolation of hyperbolic titration curves in amperometric, photometric, and other instrumental titrations. It is assumed that the titration is based upon a single-step ion-association reaction mA + nB right harpoon over left harpoon A(m)B(n) and that the measured physical property falls within known minimum and maximum values. The procedure is suitable for end-point determination, even when the titration curves have extensive curvature, and for predicting the choice of optimum experimental conditions for a given titration.     

Voltammetric,potentiometric and amperometric studies with a rotated aluminum wire electrode : Amperometric titration of fluoride with aluminum

The rotated aluminum electrode is a suitable indicator electrode in the amperometric titration of fluoride, Fluoride in concentrations varying between 1.10^-4 and 2.10^-3M was titrated with a standard aluminum nitrate solution in aqueous buffer solutions (pH between 3.6 and 46) Equilibrium was established within 15 mim. The fluoride-aluminum ratio at the (true) end-point was found to increase from 2 2 in 10^-4M fluoride to 28 in. 2.10^-3M fluoride. The titration calculated from the stability constants of the various aluminum-fluoride complexes were found to be in excellent agreement with the experimental curves.From a practical point of view titration in an acetate buffer in 50% alcohol in the presence of 0 5 M potassium or sodium nitrate is recommended. The fluoride-aluminum ratio at the end-point was found to be 5 9 ± 0 1 and independent of the fluoride concentration.     

An automatic titration control unit

A unit is described for the automatic termination of coulometric or volumetric titrations in conjunction with a suitable valve millivoltmeter and motorized buret or constant current generator. Two values of potential can be preset on the instrument, in either rising or falling sequence. On reaching the first potential, the end-point is approached by pulsed addition of the titrant ; the titration is terminated at the second potential, The on and off time cycles for the pulsing circuit are independently variable from 0.1 to 1.0 sec on and 3 to 15 sec off.     

Ultrasonic speeds and thermodynamic properties of (benzene + nitrobenzene) under high pressures

Ultrasonic speeds u in {(1?x)C₆H₆ + xC₆H₅NO₂} were measured by a fixed-path pulse technique at 293.15, 303.15, and 313.15 K under pressures up to 30 or 200 MPa with an observed error of less than 0.3 per cent. Curves of u(x) change smoothly in the benzene-rich region. But near x = 0.7, u(x) apparently deviates from a smooth curve, and the apparent gap becomes progressively greater as the temperature is reduced or the pressure is raised. From the experimental values, densities, isentropic compressibilities, and expansivities were calculated at high pressures. These quantities also show unusual behavior with x similar to that of u.     

Halon thermochemistry: Ab initio calculations of the enthalpies of formation of fluoroethanes

The ab initio G2, G2(MP2), CBS-4 and CBS-Q quantum mechanical protocols and the parameterized BAC-MP4 procedure were used to calculate the enthalpies of formation (Δ_fH⁰) of ethane and the complete series of fluoroethanes, C₂H_xF_6−x, x = 0−5. Results from all methods exhibited significant negative deviations from experiment. With the exception of the CBS-4 and BAC-MP4 procedures, the negative errors in the calculated enthalpies were observed to be linearly dependent upon the number of CF bonds in the molecule. Application of a bond additivity correction (BAC) parameter, Δ_CF, derived in an earlier investigation of fluoro- and chlorofluoromethanes, removed some although not all of the systematic deviations. Introduction of a heavy atom interaction parameter, representing the effect of an attached carbon on the CF bond error, yielded corrected enthalpies which agree with experiment to within the reported uncertainties. The BAC-MP4 method, which has already been parameterized with generalized BACs, yields calculated enthalpies which average approximately 10 kJ mol⁻¹ below the experimental values of Δ_fH⁰ in the fluoroethanes.     

The titration error in potentiometric precipitation titration

The titration error can be calculated with the aid of the value of the buffer index determined at the inflection point of the titration curve when a precipitation titration is followed with an ion-selective electrode. When the precipitate is not formed ideally in the titration (i.e., is not formed under equilibrium conditions) the titration error cannot be predicted from the values of the solubility product, nor can the values of the solubility product be calculated from titration data at the inflection point.     

Determination of cationic polyelectrolytes using a photometric titration with crystal violet as a color indicator

The reaction of the cationic dye, crystal violet (CV) with the anionic polyelectrolytes such as potassium poly (vinyl sulfate) (PVSK) results in a decrease of the absorbance of CV at the maximum absorption wavelength (590 nm). This change of the absorption spectra of the CV has been already applied to the determination of anionic polyelectrolytes using flow injection analysis method. In this paper, CV was applied to the indicator for the determination of cationic polyelectrolytes such as poly (diallyldimethylammonium chloride) (Cat-floc) by photometric titration, using a PVSK solution as a titrant. The end-point of the titration is detected as the break point of the titration curve. A linear relationship between the concentration of cationic polyelectrolyte and the end-point volume of the titrant exists in the concentration range from 0 to 5×10⁻⁵ eq. mol dm⁻³ for Cat-floc, glycol chitosan and methylglycol chitosan. The effects of the concentration of CV and coexisting electrolytes in the sample solution and the effect of pH of the sample solution on the degree of the change of absorbance at the end-point were also examined.     

Photometric titrations with indicators

Various types of photometric titration curves are discussed. If a metal M is titrated conipleximetrically using a metal indicator and the absorbance is plotted vs. the titrant consumed, the inflection point appears at a pM value defined by the equation 3 pM_infl = pM_trans + 2 pM_eqThis expression is valid when M combines in a 1 : 1 ratio with the complexing agent and the indicator and when the indicator concentration is small compared to the total metal concentration.The difference between the pM values at the inflection and equivalence points can be calculated from the equation ΔpM = pM_infl — pM_eq = $\text{1}\text{3}$(pM_trans — pM_eq) = $\text{1}\text{6}$log(C_MK²_MI/K_MY)If the inflection point is taken as the equivalence point, the error arising can be calculated from ΔpM, or more simply, read from a diagram.If transmittance, instead of absorbancc, is plotted as a function of the titrant volume, the inflection point depends on the added amount of indicator. However, at high transmittance values, i.e., at low indicator concentrations, the inflection point of a transmittance curve occurs practically at the same volume of added titrant as the inflection point of an absorbance curve. Rules are given for applying an indicator correction for the amount of metal bound to the indicator at the end-point.The derived equations and discussions can also be applied to acid-base titrations.     

Titrations with extractive end-points: The dichromate titration

A method for the titration of iron(II) with K₂Cr₂O₇ in coloured solutions is reported, using the extraction of Cr₂O₇^-2 ions as (Ph₃MeAs)₂Cr₂O₇ at the end-point. The method is applicable to titration with $\text{N}\text{10}$ K₂Cr₂O₇ in the presence of normally interfering coloured cations in molar concentrations up to 50 times that of the iron (II). The method may be used to estimate iron in ferrous alloys, usually without separation from the other metals present. A stable dichromate, (Ph₃MeAs)₂Cr₂O₇ has been isolated.     

H/P NMR pH indicator series to eliminate the glass electrode in NMR spectroscopic pKa determinations

NMR titration is an efficient method to determine pK_a values of multiprotic acids in aqueous solution. While modern 1D/2D NMR techniques yield chemical shifts with increasing precision, the glass electrode-based pH measurement becomes the limiting factor to affect the precision of the resulting dissociation constants. The pH in the NMR tube can also be deduced from the actual chemical shift of an appropriate monoprotic indicator molecule. In the present work, the in situ NMR pH measurement has been extended for the entire pH range 0-12 using indicators with overlapping ranges of dissociation. In the first, calibrating ¹H/³¹P NMR titration, limiting chemical shifts and pK were determined for each indicator. An analysis of error propagation showed that the accuracy and precision of glass electrodes can be achieved at 1.8 < pH < 12 and even exceeded at pH extremes by NMR indicators, respectively. The assembled set of indicators was applied for in situ pH monitoring in the following “electrodeless” ¹H/³¹P NMR titration of a newly synthesized aminophosphinophosphonic acid. Multivariate nonlinear parameter estimation was used to calculate the pK values that were confirmed by potentiometric titrations.     

Anomalous deuterium labeling effect on anharmonicity of the benzene ring breathing mode,v1

¹B_2u excited state anharmonicity constants have been obtained from ν₁ progressions in two-photon multiphoton ionization spectra for C₆H₆, C₆D₆, and ¹³C₆H₆, in a supersonic free jet. The diagonal anharmonicity constant, x₁₁, is found to increase in C₆D₆ to −1.18 cm⁻¹ from −0.50 cm⁻¹ in C₆H₆. It is unchanged in ¹³C₆H₆. a mechanism for the anomalous deuterium-induced increase is suggested which involves the almost purely skeletal ring breathing mode, v₁, in C₆H₆ gaining highly anharmonic C-D stretching character in C₆D₆. Excited state x_1.6,x_1.7, and x_1.14 off-diagonal constants have also been obtained for C₆H₆ by combining the two-photon analysis with ultraviolet data from Atkinson and Parmenter. The values are −1.4, −2.0, and −3.4 cm⁻¹, respectively.