Determination of Molecular Weight and Second Virial Coefficient

2 DETERMINATION OF MOLECULAR WEIGHT AND SECOND VIRIAL COEFFICIENT 

For a thermodynamically ideal solution (e.g., a very dilute solution), the osmotic pressure obeys Van t Hoff s equation  

FIGURE 9.1 Osmometers (a) Helfritz type b) Schultz type. 

The coefficients A2, A3,. .. or F2, F3,. .. are functions of the molecular weight distribution of solute, the solvent-solute system, and the temperature. Virial coefficients beyond A3 or F3 are usually of no physical interest and can be neglected. There are several ways to treat the osmotic pressure data if the plot is not linear  

The curve-fitting method can be used to determine Ai, A2, and A3 directly. 

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FIGURE 14.6 Determination of molecular weight and second virial coefficient. 

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