Molar mass determination

In carrying out a molar mass determination by freezing point depression, we must choose a solvent in which the solute is readily soluble. Usually, several such solvents are available. Of these, we tend to pick one that has the largest kf. This makes ATf large and thus reduces the percent error in the freezing point measurement From this point of view, cyclohexane or other organic solvents are better choices than water, because their kf values are larger. 

If it is possible to analyse end groups of a particular specimen of polymer, it may be possible to use the data to determine number average relative molar mass. If the molecules are branched the degree of branching can be measured from a combination of end group analysis and relative molar mass determination (determined by an alternative method). 

Fig. 4. Critical concentrations of polystyrene/toluene and polyacrylamide/water at 25 °C in relation to molar mass determined by viscometry and light scattering... 

Vapour pressure osmometry is the second experimental technique based on colligative properties with importance for molar mass determination. The vapour pressure of the solvent above a (polymer) solution is determined by the requirement that the chemical potential of the solvent in the vapour and in the liquid phase must be identical. For ideal solutions the change of the vapour pressure p of the solvent due to the presence of the solute with molar volume V/1 is given by... 

Figure 15.1. MALDI spectrum of a polycarbonate sample along with peak assignment. In the inset, an expansion of the spectral region from 3.0 up to 3.7 kDa is shown. (Reproduced from Puglisi, C. et al., 1999. Analysis of Poly(bisphenol A Carbonate) by Size Exclusion Chromatography/Matrix-Assisted Laser Desorption/lonization. I. End Group and Molar Mass Determination. Rapid Communications in Mass Spectrometry, 13 2260-2267. With permission of John Wiley Sons, Inc.)...

To get the final answer, we must divide the energy released by the moles of glucose. We find the moles of glucose from the mass given in the problem and the molar mass determined from the atomic weights of the elements. 

It took a long time before the percolation theory could be proved to be the better one in most cases. The reason for this delay resulted in part from the fact that until ten years ago the size exclusion chromatography (SEC) with on-hne light scattering was not sufficiently well developed. A direct molar mass determination is, however, imperative, since the separation in SEC is due to the hydrodynamic volume of the particles. A branched macromolecule has, however, a significantly higher molar mass than a linear one of the same hydrodynamic volume. Since 1989 a number of results have been reported which all strongly supported the percolation theory [109,111-116]. 

It is necessary to say that the molar masses of the calibration materials quoted by some suppliers may differ from the actual values. In other words, some commercial calibration materials may jump out from the calibration dependences because their molar mass determined by the producer is wrong. 

Molar mass determinations based on SDS-PAGE is sometimes misleading, since some proteins are not conversed completely into a rod-like shape or the protein/SDS ratio differs from the average. 

For characterization of a GPC medium other than defined macromolecules as dextrans, polypeptides, polystyrene sulfates, or colloidal gold may be used. For these standards the eluent is ddH20. These macromolecules are suitable for molar mass determination of proteins with restrictions only. 

Introduction and Orientation, Matter and Energy, Elements and Atoms, Compounds, The Nomenclature of Compounds, Moles and Molar Masses, Determination of Chemical Formulas, Mixtures and Solutions, Chemical Equations, Aqueous Solutions and Precipitation, Acids and Bases, Redox Reactions, Reaction Stoichiometry, Limiting Reactants... 

X V iution), the determination of the molar mass of a solute requires a measurement of mass, volume, temperature, and osmotic pressure. Osmotic pressures are generally large and can be determined quite accurately, thus yielding accurate molar masses. Boiling-point elevations and freezing-point depressions are usually small and not very accurate, so molar mass determinations based on those measures often are not accurate. 

Molar mass determination of the acetylated true graft copolymer, the separated branch after acetylation and the acetylated mother cellulose, was carried out with a high speed membrane osmometer using chloroform, benzene, and chloroform, resp., as solvents. 

Laboratory procedures Molar mass determination by freezing-point depression... 

Another option for the analysis of complex polymers is the separation with respect to chemical composition or functionality by means of interaction chromatography. In this case, functionally or chemically homogeneous fractions are obtained which can then be subjected to molar mass determination. 

Molar mass determination requires the knowledge of the specific refractive index increment Ant Ac which in the case of complex polymers depends on chemical composition. Copolymer refractive index increments (dn/dc)copo can be accurately calculated for chemically monodisperse fractions, if comonomer weight fractions and homopolymer values are known ... 

Other examples of successful combinations of liquid chromatography and MALDI-TOF have been reported by Kruger et al. who separated linear and cyclic fractions of polylactides by LC-CC [184]. Just et al. were able to separate cyclic siloxanes from linear silanols and to characterize their chemical composition [185]. The calibration of an SEC system by MALDI-TOF was discussed by Mon-taudo et al. [186]. Poly( dimethyl siloxane) (PDMS) was fractionated by SEC into different molar mass fractions. These fractions were subjected to MALDI-TOF for molar mass determination. The resulting peak maximum molar masses were... 

For the determination of very high molar masses, freezing-point depressions, boiling-point elevations, and vapor-pressure lowerings are too small for accurate measurement. Osmotic pressures are of a convenient order of magnitude, but measurements are time-consuming. The technique to be used in this experiment depends on the determination of the intrinsic viscosity of the polymer. However, molar-mass determinations from osmotic pressures are valuable in calibrating the viscosity method. 

Relative estrogenic potency compared to 17/i-estradiol (100) by molar mass determined with the recombinant yeast cell bioassay (RCBA) [138b]. Trade name. 

Using the mass percents and the molar mass, determine the mass of each element present in 1 mole of compound. 

A molar mass determination using osmotic pressure is illustrated in Example 17.4. 

Calculate the mass and moles of water originally present in the hydrate by using the molar mass determined from the periodic table. 

The attachment of halide ions to anilines may therefore afford abundant adduct ions which are valuable for selective detection and molar mass determination of the analytes. For example, Cl- attachment has proven suitable for the gas chromatography/CI-MS monitoring of human exposure to several aromatic amines112. 

In practice, SEC columns are often calibrated using linear monodisperse polystyrene standards, generating a calibration curve like Fig. 1.26. Then any linear polymer that is soluble in the same solvent, for which a Mark-Houwink equation is known, can have its molar mass determined by this calibrated SEC experiment. The elution volume of the polymer determines [q M from the calibration curve and the Mark-Houwink... 

A.D. McBrady, R. Chantiwas, A.K. Torgerson, K. Grudpan, R.E. Synovec, An absorbance-based micro-fluidic sensor for diffusion coefficient and molar mass determinations, Anal. Chim. Acta 575 (2006) 151. 

A solution of 1.00 g of anhydrous aluminum chloride, AICI3, in 50.0 g of water freezes at — 1.11°C. Does the molar mass determined from this freezing... 

The combustion of 3.795 mg of liquid B, which contains only C, H, and O, with excess oxygen gave 9.708 mg of CO2 and 3.969 mg of H2O. In a molar mass determination, 0.205 g of B vaporized at 1.00 atm and 200.0°C and occupied a volume of 89.8 mL. Derive the empirical formula, molar mass, and molecular formula of B and draw three plausible stmc-tures. 

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