Osmotic pressure mixing

In Chap. 8 we saw how the equilibrium osmotic pressure of a solution is related to AG for the mixing process whereby the solution is formed. Any difference in the concentration of the solution involves a change in AG j, ... 

Human blood has an osmotic pressure relative to water of approximately 7.7 atm at body temperature (37°C). In a hospital, intravenous glucose (C6H)2Ofc) solutions are often given. If a technician must mix 500.111L of a glucose solution for a patient, what mass of glucose should be used ... 

Fig Reduced Osmotic pressure of polystyrene solutions in mixed-solvents as a function of the concentration. 

The Osmotic pressure equilibrium in this type of osmometers is attained quick and very small quantities of solvent and solution are needed in this case. Sometimes mixed solvents may be used in this type of osmometer. The disadvantages of the osmometer Organisation and Qualities... 

As we have the free energy of mixing, we may now estimate the osmotic pressure of our dilute polymer solution ... 

If you have a class with biochemists, clearly the area of enzyme kinetics is practically mandatory. If biologists are mixed in with the biochemists, osmotic pressure is an important concept to cover carefully and a concept typically not well covered in general chemistry and in most physical chemistry texts or classes. A quick example what is a 2 Osmolar solution of sodium chloride Such concentration units are used when dispensing various saline solutions in hospitals. What is the origin of the unit A 1 M NaCl solution dissociates into two ions that would double the osmotic pressure of a non dissociating solute. Thus, the 1 M solution of NaCl becomes a 2 Osmolar solution. Other examples abound - the bursting pressure of a cell relates to the osmotic pressure of the serum in which the cell finds itself. 

We present a review of theoretical and experimental results on the swelling behavior and collapse transition in polymer gels obtained by our group at Moscow State University. The main attention is paid to polyelectrolyte networks where the most important factor is additional osmotic pressure created by mobile counter ions. The influence of other factors such as condensation of counter ions, external mechanical force, the mixed nature of low-molecular solvents, interaction of network chains with linear macromolecules and surfactants etc. is also taken into account Experimental results demonstrate a good correlation with theoretical analysis. 

The contribution fl>3 corresponds to the difference between the osmotic pressure in the ionized gel and in external solution (mixing of ions with the slovent). From the Donnan equilibrium we obtain... 

The recent systematic investigations carried out by Newman et al. [37] were devoted to the viscosity, sedimentation, diffusion and osmotic pressure of nitro-celluloses prepared by nitrating non-purified cotton, purified cotton, and viscose fibres with mixed add containing phosphoric acid and phosphoric anhydride. 

We can express the free energy of gel in terms of the above quantities, and calculate from it the osmotic pressure 7t acting on the network. For a gel to be in equilibrium with the outer solvent, n must be zero. Several different mechanisms are known to contribute to 7t, the mixing process, the rubber elasticity, and counter ions, etc. The osmotic pressure due to mixing is expressed as... 

Fig. la, h. The elastic part (ne) and the negative of the mixing part (— Jtm) of the osmotic pressure as functions of polymer concentration < >. The intercepts of ae and — nm correspond to the equilibrium state of neutral gels. Numbers besides each curve of — represent Xi> which increases with temperature, (a) x2 = 0. Only one root at all temperatures, (b) Xi = 0.56. Three roots appear in the intermediate temperature range (around Xi = 0.465), which correspond to stable, unstable, and metastable states, respectively. (Reproduced with permission from Ref. 20)... 

Fig. 2. The sum of the elastic and the ionic parts (ne + iq) and the negative of the mixing part ( — n ) of the osmotic pressure as functions of polymer concentration 4- The calculation was made forf= 10 and = 0. Note that the ordinate scale is fifty times larger than in Fig. 1. The intercepts of...

Flory [3] formalized the equation of state for equilibrium swelling of gels. It consists of four terms the term of rubber-like elasticity, the term of mixing entropy, the term of polymer solvent interaction and the term of osmotic pressure due to free counter ions. Therefore, the gel volume is strongly influenced by temperature, the kind of solvent, free ion concentrations and the degree of dissociation of groups on polymer chains. 

The final colligative property, osmotic pressure,24-29 is different from the others and is illustrated in Figure 2.2. In the case of vapor-pressure lowering and boiling-point elevation, a natural boundary separates the liquid and gas phases that are in equilibrium. A similar boundary exists between the solid and liquid phases in equilibrium with each other in melting-point-depression measurements. However, to establish a similar equilibrium between a solution and the pure solvent requires their separation by a semi-permeable membrane, as illustrated in the figure. Such membranes, typically cellulosic, permit transport of solvent but not solute. Furthermore, the flow of solvent is from the solvent compartment into the solution compartment. The simplest explanation of this is the increased entropy or disorder that accompanies the mixing of the transported solvent molecules with the polymer on the solution side of the membrane. Flow of liquid up the capillary on the left causes the solution to be at a hydrostatic pressure... 

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