Molarities, effective, experimental

When standardizing a solution of NaOH against potassium hydrogen phthalate (KHP), a variety of systematic and random errors are possible. Identify, with justification, whether the following are systematic or random sources of error, or if they have no effect. If the error is systematic, then indicate whether the experimentally determined molarity for NaOH will be too high or too low. The standardization reaction is... 

In the last two decades, there has been a large accumulation of experimental evidence as well as of theoretical interpretations of intramolecular reactions. One notes, however, that attention has been focused on the phenomena of immediate interest to the various specialists. As a consequence of the fact that specialisation implies intensification of knowledge on the one hand but limitation on the other, there has still been insufficient communication and cross-fertilisation between the different schools. This situation is well exemplified by the two most extensive reviews on intramolecular phenomena, namely, that of Kirby (1980), entitled Effective Molarities for Intramolecular Reactions , and that of Winnik (1981a), entitled Cyclisation and the Conformation of Hydrocarbon Chains , which present different approaches and apparently unrelated facts and theories. 

The effect of the solute on the vapor pressure of a solution gives us a convenient way to count molecules and thus provides a means for experimentally determining molar masses. Suppose a certain mass of a compound is dissolved in a solvent, and the vapor pressure of the resulting solution is measured. Using Raoult s law, we can determine the number of moles of solute present. Since the mass of this number of moles is known, we can calculate the molar mass. 

Available experimental values of the refractive index were used to calculate "experimental" values of the molar refraction RLL by using Equation 8.3. Equation 9.8 was then used to calculate the "experimental" effective dipole moments at room temperature for the 40 polymers from the dataset for which all of the necessary information was available to calculate both PLl and RT i from experimental data. "Fitted" values of RT T, calculated as described in Section 8.E, were then combined with the fitted values of PT T, to estimate the effective dipole moment. 

Figure 9.6. Comparison of the "experimental" effective dipole moment p.(298K) at room temperature, calculated from observed dielectric constants, refractive indices and molar volumes, with l(298K) calculated from the values predicted for the same properties by using the new correlations developed in this book, for 40 polymers. 

Note well as this is important the concentration which appears in this expression is always a stoichiometric concentration. All experimentally determined molar conductivities are therefore based on stoichiometric concentrations. However, in the theoretical descriptions of conductance, the arguments are generally given in terms of actual concentrations. Being aware of this distinction is vital in the theoretical description of the effect of non-ideality on molar conductivity (see Chapter 12). It is also important in the theoretical analysis of the determination of the degree of ionisation of very weak acids, or the degree of protonation of very weak bases, using conductance measurements (see Section 11.14). 

The effective magnetic moment, can be obtained from the experimentally measured molar magnetic susceptibility, Xm, and is expressed in Bohr magnetons p ) where l B = eh/Attm = 9.27 x 10 JT . Equation 20.12 gives the relationship between and Xml using SI units for the constants, this expression reduces to equation 20.13 in which Xm is in cm moU. In the laboratory, the continued use of Gaussian units in magnetochemistry means that irrational susceptibility is the measured quantity and equation 20.14 is therefore usually applied. ... 

The effective magnetic moment, can be obtained from the experimentally measured molar magnetic susceptibility, Xm (see Box 21.5), and is expressed in Bohr magnetons ( b) where lpB = eh/Anm = 9.27 x 10 " JT. Equation... 

In this approach, connectivity indices were used as the principle descriptor of the topology of the repeat unit of a polymer. The connectivity indices of various polymers were first correlated directly with the experimental data for six different physical properties. The six properties were Van der Waals volume (Vw), molar volume (V), heat capacity (Cp), solubility parameter (5), glass transition temperature Tfj, and cohesive energies ( coh) for the 45 different polymers. Available data were used to establish the dependence of these properties on the topological indices. All the experimental data for these properties were trained simultaneously in the proposed neural network model in order to develop an overall cause-effect relationship for all six properties. 

The gas phase mass transfer coefficient for the absorption of ammonia into water from a mixture of composition NHj 20%, N2 73%, Hj 7% is found experimentally to be 0.030 m/s. What would you expect the transfer coefficient to be for a mixture of composition NH3 5%, N2 60%, Hj 35% All compositions are given on a molar basis. The total pressure and temperature are die same in both cases. The transfer coefficients are based on a steady-state film model and the effective film thickness may be assumed constant. Neglect the solubility of Ny and Hi in water. 

Experimentally, fCsp = 1.6 X 10 10 at 25°C, and the molar solubility of AgCl in water is 1.3 X 10 5 mol-IT. If we add sodium chloride to the solution, the concentration of Cl ions increases. For the equilibrium constant to remain constant, the concentration of Agf ions must decrease. Because there is now less Ag+ in solution, the solubility of AgCl is lower in a solution of NaCl than it is in pure water. A similar effect occurs whenever two salts having a common ion are mixed (Fig. 11.16). 

On the basis of the experimental results, Sn02-Zr02 catalysts were prepared by the coprecipitation method. That is, Sn02 and Z1O2 were mixed chemically rather than physically. The effects of the Sn/Zr molar ratio and reaction temperature on the SO2 conversion and sulfur yield for Sn02-Zr02 catalysts were... 

The final structure of resins produced depends on the reaction condition. Formaldehyde to phenol (F/P) and hydroxyl to phenol (OH/P) molar ratios as well as ruction temperahne were the most important parameters in synthesis of resols. In this study, the effect of F/P and OH/P wt%, and reaction temperature on the chemical structure (mono-, di- and trisubstitution of methyrol group, methylene bridge, phenolic hemiformals, etc.) was studied utilizing a two-level full factorial experimental design. The result obtained may be applied to control the physical and chemical properties of pre-polymer. 

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