Avogadro constant refractive index

Absolute methods provide the molecular weight and the degree of polymerization without any calibration. Their calculation from the experimental data requires only universal constants such as the gas constant and Avogadro s number, apart from readily determinable physical properties such as density, refractive index, etc. The most important methods in use today are mass spectrometry, osmometry, light scattering, and - to some extent - sedimentation and diffusion measurements. Also, some chemical and spectroscopic methods (determination of end-groups) are important because of their relative simplicity. 

K is also known as the Debye constant [9], NA is Avogadro s number, and n0 is the refractive index of the pure solvent. 

The refractive index, nD, defined as the ratio of light speed at the sodium D-line in a vacuum to that in the medium, is used in obtaining the polarizability, a, of solvent molecules. The relationship between a and nD is given by a = (3Vm/ 4 rNA)( D-l)/(wD + 2), where NA is the Avogadro constant and Vm is the molar volume.4 Solvent molecules with high a-values tend to interact easily with one another or with other polarizable solute particles by dispersion forces.5 ... 

In these equations ns is the solvent refractive index, dn/dc the refractive index increment, c the polymer concentration in g/ml, T the temperature in K, R the gas constant, NA Avogadro s number, and n the osmotic pressure. Equation (B.8) follows from Eq. (B.7) by using the familiar virial expansion of the osmotic pressure... 

Mass of a molecule Mass of proton Mass of ion Concentration Avogadro constant Complex refraction index Optical refraction index Polarization... 

Some of the factors in the foregoing equation are instrument constants and are determined independently of the actual light scattering measurement. These include no (refractive index of pure solvent at the experimental temperature and wavelength) L (Avogadro s constant) X, which is set by the experimenter and r, an instrument constant. 

X is the wavelength of the incident light, Na is the Avogadro number, v is the specific refractive index increment, M is the weight average molecular weight, and Kls is the instrument constant. 

Generally dn/dc maybe taken as a constant characteristic of the solute and independent of c over a considerable range in dilute solutions, so we may write 3w/3c = ( — w )/c, where 0 is the refractive index of the solvent. (N is Avogadro s number, and c is expressed as g. solute/cc. solution.)... 

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