Mass average relative molecular

Epikote 1001 is a synthetic epoxy resin with an average relative molecular mass of 900... 

Monoisotopic vs. chemical (average) relative molecular mass... 

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

Rule 1.8 Specifications about mass fractions (w), mole fractions (x), molar masses (A/), relative molecular masses (M-), degrees of polymerization (DP) or the average values of the latter three quantities, may be expressed by placing the corresponding values in parentheses after the formula of the macromolecule in a manner analogous to that recommended for the naming of copolymers [6]. 

The translational entropy is high about 120 J/deg/mol (30 cal/deg/mol) for a 1 -M solution of a small molecule. This is equivalent to about 40 kJ/mol (9 kcal/mol) at 25°C (298 K). The translational entropy is proportional to the volume occupied by the molecule the smaller the volume, the more the molecule is restricted and the lower the entropy. Similarly, the entropy decreases with increasing concentration, since the average volume occupied by a molecule is inversely proportional to its concentration. It is important to note that the dependence on mass is low (Table 2.3). A 10-fold increase in mass on going from, say, a relative molecular mass of 20 to one of 200 leads to only a small increase in translational entropy. 

Colloidal systems are generally of a polydispersed nature - i.e. the molecules or particles in a particular sample vary in size. By virtue of their stepwise build-up, colloidal particle and polymer molecular sizes tend to have skew distributions, as illustrated in Figure 1.2, for which the Poisson distribution often offers a good approximation. Very often, detailed determination of relative molecular mass or particle size distribution is impracticable and less perfect experimental methods, which yield average values, must be accepted. The significance of the word average depends on the relative contributions of the various molecules or particles to the property of the system which is being measured. 

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 ... 

In contrast to osmotic pressure, light-scattering measurements become easier as the particle size increases. For spherical particles the upper limit of applicability of the Debye equation is a particle diameter of c. A/20 (i.e. 20-25 nm for A0 600 nm or Awater 450 nm or a relative molecular mass of the order of 10 ). For asymmetric particles this upper limit is lower. However, by modification of the theory, much larger particles can also be studied by light scattering methods. For polydispersed systems a mass-average relative molecular mass is given. 

If a polymer molecule in solution behaves as a random coil, its average end-to-end distance is proportional to the square root of its extended chain length (see page 25) - i.e. proportional to Ai 5, where Mr is the relative molecular mass. The average solvated volume of the polymer molecule is, therefore, proportional to M 5 and, since the unsolvated volume is proportional to A/r, the average solvation factor is proportional to (i.e. Af 5). The intrinsic viscosity of... 

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

Make appropriate extrapolations and calculate an average relative molecular mass for the cellulose nitrate. 

K and a in the expression, [17] = KM , are 3.7 x 10-5 m3 kg-1 and 0.62, respectively, for this polymer-solvent system. Assuming a constant density for the solutions, calculate an average relative molecular mass for the polystyrene sample. How would this relative molecular mass be expected to compare with the relative molecular mass of the same sample of polystyrene in toluene determined from a) osmotic pressure and (b) light-scattering measurements ... 

Relative molecular mass Some of the average atomic masses found in a compound. 

The relative molecular mass that is determined by the mass spectrometer is numerically different from the chemical (average) molecular mass used to calculate molar concentrations or reaction stoichiometries. For the elements... 

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