Bases strength measurement

The base strength measurements suggest that the organotin sulphides such as (CH3)3SnSSnfCH3)3 are stronger bases than the simple organic sulphides. This would be in accord with little or no back-bonding from sulphur to tin, and tin s lower electro-... 

A new, non destructive method has been developed for testing high strength bolts which is based on measuring the magnetic stress on the head of a bolt. The forces originating in the body of the bolt can be determined in this way since these forces are proportional to the stress state in the head of the bolt. 

The University developed a method of determination of the material residual strength, based on measurement of the change of phase velocity of ultrasonic waves, as well as an ultrasonic flaw detector-tomograph with multi-element transducers of the type of phased acoustic array. It enables control of the internal structure of materials and products of up to 300 mm thickness, with the resolution of up to 0.5 mm. In the same university, work on NDT is also carried out in the welding and electro-acoustic departments. 

Basicity constant Ki, (Section 1 14) A measure of base strength especially of amines... 

Analytical Methods. Analysis of fresh and spent peroxides and superoxides is done by adding the material to water. Approximately 0.1 wt % permanganate is used in the water to decompose the peroxide ion which otherwise forms. The evolved oxygen is measured volumetricaHy. If the material is spent, the base strength is titrated to a phenolphthalein end point, acidified further, and the carbon dioxide is deterrnined volumetricaHy. 

Properties of copper—tin—lead alloys are Hsted in Table 10. The members of the tin bronze alloy group are cast using the centrifugal, continuous, permanent, plaster, and sand molding methods. Leaded tin—bronze alloys have minimum tensile strengths of 234—248 MPa (34,000—36,000 psi) as cast in sand molds, whereas the minimum tensile strengths for high leaded tin—bronze alloys are 138—207 MPa (20,000—30,000). The values are based on measurement of test bars cast in sand molds. 

Color Difference Evaluation. Shade evaluation is comparable in importance to relative strength evaluation for dyes. This is of interest to both dye manufacturer and dye user for purposes of quaUty control. Objective evaluation of color differences is desirable because of the well-known variabihty of observers. A considerable number of color difference formulas that intend to transform the visually nonuniform International Commission on Illumination (CIE) tristimulus color space into a visually uniform space have been proposed over the years. Although many of them have proven to be of considerable practical value (Hunter Lab formula, Friele-MacAdam-Chickering (FMC) formula, Adams-Nickerson formula, etc), none has been found to be satisfactorily accurate for small color difference evaluation. Correlation coefficients for the correlation between average visually determined color difference values and those based on measurement and calculation with a formula are typically of a magnitude of approximately 0.7 or below. In the interest of uniformity of international usage, the CIE has proposed two color difference formulas (CIELAB and CIELUV) one of which (CIELAB) is particularly suitable for appHcation on textiles (see Color). 

Most organic compounds are bases, that is, they are capable of accepting a proton. The best-studied organic bases are the moderately strong ones, which will receive a proton in dilute aqueous solutions amines are the most important examples. The pKa value of the protonated base, referred to the infinitely dilute aqueous solution, is the usual measure of base strength, and the pH of the solution is a quantitative measure of solvent acidity, or ability to transfer a proton. 

Recently Stamhuis et al. (33) have determined the base strengths of morpholine, piperidine, and pyrrolidine enamines of isobutyraldehyde in aqueous solutions by kinetic, potentiometric, and spectroscopic methods at 25° and found that these enamines are 200-1000 times weaker bases than the secondary amines from which they are formed and 30-200 times less basic than the corresponding saturated tertiary enamines. The baseweakening effect has been attributed to the electron-withdrawing inductive effect of the double bond and the overlap of the electron pair on the nitrogen atom with the tt electrons of the double bond. It was pointed out that the kinetic protonation in the hydrolysis of these enamines occurs at the nitrogen atom, whereas the protonation under thermodynamic control takes place at the -carbon atom, which is, however, dependent upon the pH of the solution (84,85). The measurement of base strengths of enamines in chloroform solution show that they are 10-30 times weaker bases than the secondary amines from which they are derived (4,86). 

Basicity constant, Kh (Section 24.3) A measure of base strength. For any base B, the basicity constant is given by the expression... 

To use the above expression for measuring the strength of an acid, a standard acid-base pair, say A2-B2, must be chosen, and it is usually convenient to refer acid-base strength to the solvent. In water the acid-base pair H30 + -H20 is taken as the standard. The equilibrium defining acids is therefore ... 

The proton-donating strength of an acid is measured by its acidity constant the proton-accepting strength of a base is measured by its basicity constant. The smaller the constants, the weaker the respective strengths. The larger the value of pK, the weaker the acid or base. 

The properties of excited states are not easy to measure because of their generally short lifetimes and low concentrations, but enough work has been done for us to know that they often differ from the ground state in geometry, dipole moment, and acid or base strength. For example, acetylene, which is linear in the ground state, has a trans geometry... 

Based on the above arguments, with peel strength measurements for the three SUV/Minivan tires. We will also include the elongation to break data for the Large Car-C tire even though the difference in wedge rubber modulus between the held and oven sets makes the comparison between these data sets somewhat questionable. 

Basicity measures base strength (or how unstable the base is) by the position of equilibrium. The term basicity does not reflect how quickly the equilibrium was reached. The equilibrium might have been established in a fraction of a second or it could have taken several hours. It doesn t matter, because we are not measuring speed of reaction. We are measnring stability and the position of the eqnilibrinm. 

The strength of acids and bases is measured on a pH (potential of hydrogen) scale pH = -logio [H+]... 

Base strength refers to the relative tendency to produce OH- ions in aqueous solution by (1) the dissociation of soluble metal hydroxides or (2) by ionization reactions with water using Arrhenius theory. A more general definition, applying Bronsted-Lowry theory, is that base strength is a measure of the relative tendency to accept a proton from any acid. 

The small difference between the successive pK values (cf. values below) of tungstic acid was previously explained in terms of an anomalously high value for the first protonation constant, assumed to be effected by an increase in the coordination number of tungsten in the first protonation step (2, 3, 55). As shown by the values of the thermodynamic parameters for the protonation of molybdate it is actually the second protonation constant which has an abnormally high value (54, 58). An equilibrium constant and thermodynamic quantities calculated for the first protonation of [WO, - pertaining to 25°C and zero ionic strength (based on measurements from 95° to 300°C), namely log K = 3.62 0.53, AH = 6 13 kJ/mol, and AS = 90 33 J, are also consistent with a normal first protonation (131) (cf. values for molydate, Table V). 

Directions for Future Work. The measurement of rates of proton transfer from a single acid to more bases differing only in thermodynamic base strength should allow the construction of BrjSnsted plots of kinetic versus thermodynamic acidity. The bases we have used at this early stage of development of the subject have involved different proton acceptor atoms and cannot be so used (although comparison of the Et N transfer rates of... 

A number of tetracyanoethylene (TCNE) n complexes of mono-substituted [2.2]paracyclophanes were examined both spectroscopically and kinetically. The position of max of the longest-wavelength charge-transfer band in the UV spectrum of the complexes, and in some cases estimated equilibrium constants 76> were used as a measure of the relative 7t-base strengths of the substituted cycles 15>. From the results of this investigation it was at once clear that complexes of tetracyanoethylene and [2.2]paracyclophane with electron-releasing substituents (Type A,... 

Methods for determining permanent dipole moments and polarizabilities can be arbitrarily divided into two groups. The first is based on measuring bulk phase electrical properties of vapors, liquids, or solutions as functions of field strength, temperature, concentration, etc. following methods proposed by Debye and elaborated by Onsager. In the older Debye approach the isotope effects on the dielectric constant and thence the bulk polarization, AP, are plotted vs. reciprocal temperature and the isotope effect on the polarizability and permanent dipole moment recovered from the intercept and slope, respectively, using Equation 12.5. 

One can analogously measure base strength via which refers to equation 18 ... 

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