Osmotic pressure

 

Osmotic pressure (atmospheres)

Sodium chloride                                 Sucrose

 

Molality

Eqn 1

Eqn 2

Experimental

Eqn 1

Eqn 2

Experimental

0.1

2.44

4.48

4.56

2.35

2.39

2.65

0.5

12.1

22.4

22.5

11.1

12.4

13.1

1.0

23.7

45.2

45.8

20.4

25.4

27.3

2.0

46.9

96.0

96.5

35.0

58.0

56.2

3.0

68.7

153.0

154.4

46.1

93.2

90.1

4.0

89.7

217.7

220.3

54.6

134.0

126.9

5.0

107.1

291.2

294.8

61.5

176.2

NA

 

Equation 1: p V  = n R T

 

Equation 2:  p v1  = R T  ln ( P1* / P1 )


Where v1 = partial molal volume of water
P1* = vapor pressure of pure water
P1 = vapor of pressure of water in solution

The idea is that Equation 1 is OK for substances such as sucrose that are not ionized. Equation 2 is required for ionic compounds.