Number-average relative molecular mass

Osmotic pressure, which is a colligative property, depends simply on the number of solute molecules present and so yields a number-average relative molecular mass ... 

Figure 3.20. The time-of-flight SIMS spectrum of a polystyrene oligomer whose number average relative molecular mass is 4964, deposited as a thin film on a silver substrate. After Bletsos et al. (1987).

Figure 6.23. The eifect of polydispersity on the interfacial tension. The interfacial tension between polybutadiene (M = 4100 and Mv,/M = 1.40) and polystyrene samples made by blending three fractions of narrow relative molecular mass to achieve a constant number average relative molecular mass (M — 5500) and various polydispersity indices was measured at 150 °C. After Nam and Jo (1995).

Hence equation (8.1.3) could be used to analyse surface pressure data to obtain number average relative molecular masses from the intercept at = 0 of a plot of yr/Fs as a function of Fg. The interpretation of the virial coefficients in molecular terms depends on which theory is used Huggins (1965) has collected together the correspondences between the virial coefficients for each of the theories. For the case of the original Singer derivation... 

For polydispersed systems an average relative molecular mass intermediate between number-average (a = 0) and mass-average (a = 1) usually results. 

Calculate the number average and weight average relative molecular mass for a sample of polystyrene made by blending eight separate fractions, each of which has a very narrow molecular mass distribution, as follows ... 

Number average molecular weight Relative molecular mass Weight average molecular weight Meter... 

Molecular mass is the average mass of a compound obtained when an accounting is made for all isotopes of the elements present based on their relative abundances, e.g., C = 12.0108 Da, O = 15.9994 Da. If the instrument used cannot resolve the individual isotopes, the observed peaks include all isotopes present. Molecular mass is sometimes referred to as average mass. For cholesterol the molecular (average) mass is 386.6616 Da. (Note the difference between this number and the mono-isotopic exact mass value, 386.3549 Da, as described above.) Molecular mass does have a dimension as it is an absolute value unit, based on 1/12 of the mass of the isotope (in lUPAC units), i.e., 1.6605 x 10- kg. If, however, the mass of an analyte is considered as a ratio with respect to the mass of C, then the dimensions cancel out and the resulting dimensionless number is the relative molecular mass. These two terms are equivalent in everyday usage. 

Figure 2.27. Profiles of the average number of monomers belonging to the same chain near a free surface in a variable density lattice model of a poly(dimethyl siloxane) melt. The relative molecular mass is 3720, the layer thickness is 2.79 A mid the temperature is 30 °C. After Theodorou (1989).

As a result of polydispersity of the compounds, the measured relative molecular masses are weighted averages of the relative molecular masses of all the individual components. Depending on the method used, the weighting can be based on the number of molecules containing the sample (osmotic pressure, vapor pressure osmometry, depression of freezing point), on their weight proportion with respect to the... 

According to ISO 31-8, the term "Molecular Weight" has been replaced by "Relative Molecular Mass", symbol M,. Thus, if this nomenclature and notation were to be followed in this publication, one would write Af,j, instead of the historically conventional M for the number average molecular weight, with sinular changes for M , Mj, and Mv, and it would be called the "Number Average... 

The average mass of all molecules of a compound is its molecular mass (formerly called molecular weight). The molecular mass of a compound is calculated by multiplying the atomic mass of each element by the relative number of atoms of the element, then adding all the values obtained for each element in the compound. For example, the molecular mass of NH3 is 14.0 + 3 x 1.0 = 17.0. For another example, consider the following calculation of the molecular mass of ethylene, C2H4 ... 

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