Colligative properties osmosis

Osmotic pressure is a third common type of colligative property. Osmosis is the transport of a pure solvent into solution through a semipermeable membrane. The membrane allows passage of solvent but restricts flow of the solute. Figure 8.24 shows the equilibrium state from which we calculate the osmotic pressure. One compartment contains... 

Raoult s law and colligative properties (nonvolatile solutes) osmosis... 

Osmosis, like all colligative properties, results from an increase in entropy as pure solvent passes through the membrane and mixes with the solution. Perhaps the simplest explanation of osmosis is seen by looking at the molecular level (Figure 11.15). Solvent molecules on the solvent side of the membrane, because of their somewhat greater concentration, approach the membrane a bit more frequently than molecules on the solution side, thereby passing through more often. 

Colligative properties have many practical uses, including the melting of snow by salt, the desalination of seawater by reverse osmosis, the separation and purification of volatile liquids by fractional distillation, and the determination of molecular mass by osmotic pressure measurement. 

Osmotic pressure, another of the colligative properties, can be understood from Fig. 17.14. A solution and pure solvent are separated by a semipermeable membrane, which allows solvent but not solute molecules to pass through. As time passes, the volume of the solution increases while that of the solvent decreases. This flow of solvent into the solution through the semipermeable membrane is called osmosis. Eventually the liquid levels stop changing, indicating that the system has reached equilibrium. Because the liquid levels are different at this point, there is a greater hydrostatic pressure on the solution than on the pure solvent. This excess pressure is called the osmotic pressure. We can take another view of this phenomenon, as illustrated in Fig. 17.15. Osmosis can be prevented by applying a pressure to the solution. The pressure that just stops the osmosis is equal to the osmotic pressure of the solution. 

The colligative properties we will be observing are freezing-point depression, boiling-point elevation, vapor-pressure lowering, and osmosis. Put on your safety glasses for all four demonstrations. 

The last colligative property to demonstrate is osmosis. The process of osmosis is rather specialized in that it requires a semipermeable membrane a material that will allow solvent molecules to pass through but not solute molecules. In osmosis, solvent flows from one solution to the other through the semipermeable membrane. If both containers are open to the same atmospheric pressure, the direction of the flow is from the more dilute solution and into the more concentrated solution. 

As osmosis proceeds, pressure builds up on the side of the membrane where volume has increased. Ultimately, the pressure prevents more water from entering, so osmosis stops. The osmotic pressure of a solution is the pressure needed to prevent osmosis into the solution. It is measured in comparison with pure solvent. The osmotic pressure is directly related to the different heights of the liquid on either side of the membrane when no more change in volume occurs. Osmotic pressure depends on the temperature and the original concentration of solute. Interestingly, it does not depend on what is dissolved. Two solutions of different solutes, for example alcohol and sugar, will each have the same osmotic pressure, provided they have the same concentration. Osmotic pressure is therefore a colligative property of solutions, one which depends only on the concentration of dissolved particles, not on their chemical identity. 

I See the Saunders Interactive General Chemistry CD-ROM, Screen 14.9, Colligative Properties (3) Osmosis. 

The pressure required to prevent osmosis from a pure solvent into a solution is called osmotic pressure. Osmotic pressure is proportional to the molarity (the number of particles of solute) of the solution and thus it is a colligative property of solutions, and the osmotic pressure of a pure solvent is zero. 

The osmotic pressure can be calculated from the solution concentration at any temperature. How do we determine "solution concentration" Recall that osmosis is a colligative property, dependent on the concentration of solute particles. Again, it becomes necessary to distinguish between solutions of electrolytes and nonelectrolytes. For example, a 1 M glucose solution consists of 1 mol of particles per liter glucose is a nonelectrolyte. A solution of 1 M NaCl produces 2 mol of particles per liter (1 mol of Na+ and 1 mol of CH). AIM CaClj solution is 3 M in particles (1 mol of Ca + and 2 mol of CH per liter). 

Osmotic Pressure The fourth colligative property appears when two solutions of different concentrations are separated by a semipermeabie membrane, one that allows solvent, but not solute, molecules to pass through. This process is called osmosis. Organisms have semipermeabie membranes that regulate internal cellular concentrations by osmosis. You apply the principle of osmosis when you rinse your contact lenses, and your kidneys maintain fluid volume osmotically by controlling Na concentration. 

Examine a system in which a dilute solution is separated from a concentrated solution by a semipermeable membrane, illustrated in Figure 14.23. During osmosis, water molecules move in both directions across the membrane, but the solute molecules cannot cross it. Water molecules diffuse across the membrane from the dilute solution to the concentrated solution. The amount of additional pressure caused by the water molecules that moved into the concentrated solution is called the osmotic pressure. Osmotic pressure depends on the number of solute particles in a given volume of solution and is a colligative property of solutions. 

Osmosis is a colligative property and its theoretical treatment is similar to that for the lowering of vapor pressure. The membrane can be regarded as equivalent to the liquid-vapour interface, i.e. one that permits free movement of solvent molecules but restricts the movement of solute molecules. The solute molecules occupy a certain area at the interface and therefore inhibit solvent egress from the solution. Just as the development of a vapor pressure in a closed system is necessary for liquid-vapour equilibrium, the development of an OSMOTIC pressure on the solution side is necessary for equilibrium at the membrane. 

Osmotic pressure is also a colligative property. Before we talk about osmotic pressure let s turn our attention to the process of osmosis. Consider two solutions that are made out of the same solvent with different concentrations of solute separated by a semipermeable membrane. The solvent will flow through the semipermeable membrane from the solution of lower concentration to the solution of higher concentration. Thus, osmosis is defined as the flow of solvent through a semipermeable membrane resulting in the equilibrium of concentrations on both sides of the semipermeable membrane. 

Osmotic pressure, another of the colligative properties, can be understood from Fig. 17.14. A solution and pure solvent are separated by a semiperme-able membrane, which allows solvent but not solute molecules to pass through. As time passes, the volume of the solution increases, whereas that of the solvent decreases. This flow of solvent into the solution through the semipermeable membrane is called osmosis. Eventually the liquid levels stop... 

Cured resins behave as semi-impermeable membranes allowing water to diffirse but acting as a barrier to larger molecules so that osmosis can occur. Therefore, if the resin contains water-soluble impurities, thermodynamics will drive the water into the resin. Osmotic pressure (rr) is a colligative property and is directly proportional to the molal concentration of the impurity. As shown in Eqn (12.8) ... 

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