Water 7 



to the total number of particles of solute, irrespective of their kind and size. 

 A number of properties of solutions, the colligative properties such as vapor 

 pressure, boiling point, freezing point, and osmotic pressure, arc tiuis related 

 to the number of particles of solute. Dilute solutions behave like gases; hence 

 the osmotic pressure (tt) equals the molal concentration (C) multiplied by 

 the gas constant (R=0.082 Hter atmosphere) and the absolute temperature 

 (T), (tt^CRT). The higher the concentration of solute, the greater are the 



S5- - 



-3 



5.0- 



4.5- 



o ''-^-^ 



Z 3.0--^ < 



0^ 



2.5-- 



2.0- 



1.5— 



1.0— - 



0.5- 



Fig. 2. The relation between lowering of the freezing point and concentration 

 of NaCl in molarity and gm./lOO cc. 



osmotic pressure, the decrease in vapor pressure, the elevation of the boiling 

 point, and the depression of the freezing point of the solution. 



Any one of the colHgative properties can be calculated from any of the 

 others In practice osmotic pressure of body fluids is not ordinarily measured 

 directly, but usually either the depression of the freezing point A rp. or the 

 vapor pressure is measured. A molal aqueous sobtion of nonelectrolyte f eeze 

 at T.86°C. The symbolA indicates lowering of a freezing point; A., e ers 

 to the medium C.,=outside), A. refers to the blood (.-mside), Au refers 

 to urine. 



