Semipermeable Allowing passage

Electrochemical Reactions. Consider a simple galvanic cell, composed of two metal electrodes, zinc and copper, immersed in two different aqueous solutions of unit activity—in this case, 1.0 M ZnS04 and 1.0 M CUSO4, respectively, connected by an electrical circuit, and separated by a semipermeable membrane (see Figure 3.8). The membrane allows passage of ions, but not bulk flow of the aqueous solutions from one side of the cell to the other. Electrons are liberated at the anode by the oxidation (increase in the oxidation number) of the zinc electrode ... 

A semipermeable membrane allows only certain types of molecules to pass through. Typical membranes allow passage of water and small molecules, but not large molecules or ions. 

Interstitial fluid is essentially an ultrafiltrate of blood plasma (see Figure 46-1). When all extracellular spaces except plasma are included, the volume accounts for about 26% ( 17 L) of the total body volume. Plasma is separated from the interstitial fluid by the endothehal lining of tbe capillaries, which acts as a semipermeable membrane and allows passage of water and diffusible solutes but not compounds of large molecular mass, such as proteins. However, this impermeability is not absolute, as demonstrated by the varying (although low) concentration of protein in intersti-... 

Imagine a semipermeable membrane that prevents passage of A molecules, but allows passage of B molecules. The difference of pressure across this membrane is called the osmotic pressure of A molecules (see Section 1.7.1). The osmotic pressure is defined as the rate of change of the total free energy of the system ATmix = nAFmix with respect to volume at constant number of A molecules ... 

Reverse osmosis employs a semipermeable membrane that allows passage of the solvent molecules, but not those of the dissolved organic and inorganic material. A pressure gradient is applied to cause separation of the solvent and solute. Any components that may damage or restrict the function of the membrane must be removed before the process is performed. Capital investment and operating costs depend on the waste stream composition. 

The polyelectrolyte also affects the distribution of coions (small ions having a charge of the same sign). This is known as the Donnan effect, which may be illustrated by envisaging a system with two compartments that are separated by a semipermeable membrane. This membrane does not allow passage of polymers but is permeable for small ions. Assume that one compartment initially contains the polyelectrolyte (PEZ ) and sufficient counterions (Na+) to neutralize the charge, while the other compartment initially contains NaCl. At equilibrium, the activity of NaCl (which means the free ion activity a+) must be equal in both compartments. This implies that CD will diffuse towards the other compartment, and the condition of... 

NeuraWrap Integra Life Sciences Type I collagen Semipermeable inner membrane allows passage of small molecules but prevents escape of growth factor outer membrane prevents scar ingrowth... 

Encapsulation of an electroactive area with a polymer which should serve as a barrier layer is very often the most challenging step in the whole sensor fabrication process. The most needed barrier is a layer that protects the electroactive area and does not allow passage of a charge through it. The second type of barrier layer is semipermeable, allowing a transport of charge... 

The Colloid-Osmotic Pressure. Besides semipermeable membranes which allow passage only for water and not for dissolved substances, there are also those which allow substances of low molecular weight, but not of high molecular weight, to penetrate. It can easily be seen that there may be pores whose diameter is smaller than that of protein molecules. In this case, salts can diffuse freely and give no cause for differences in pressure, while the law of osmosis still applies to macromolecules. Since the number of macromolecules is relatively small, the pressures that result from them commonly are small, too. The organism, however, can develop mechanical... 

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... 

When a polymer solution is separated from the pure solvent by a semipermeable membrane that allows passage of the solvent but not the solute, then (as shown in Fig. 8.4) the tendency to equalize concentrations results in flux of the solvent across the membrane and into the solution. As mass transfer proceeds, a pressure head builds up on the solution side, tending to slow down and ultimately stop the flow of solvent through the membrane. At equilibrium, the liquid levels in the two compartments differ by h units the difference in pressure % is known as the osmotic pressure of the solution. Note that if additional pressure is applied to the solution, solvent can be made to flow back to the solvent side from the solution side this is known as reverse osmosis. As the following analysis demonstrates, osmotic pressure can be employed to measure the number-average molecular weight of a polymeric solute. 

Osmosis is the movement of solvent molecules through a semipermeable membrane. The membrane is a thin, pliable sheet of material, perforated with molecular-scale holes. The holes are large enough to allow water molecules to pass back and forth through the membrane, but too small to allow the passage of solute molecules or hydrated ions hence, the membrane is semipermeable. 

If you were to place a solution and a pure solvent in the same container but separate them by a semipermeable membrane (which allows the passage of some molecules, but not all particles) you would observe that the level of the solvent side would decrease while the solution side would increase. This indicates that the solvent molecules are passing through the semipermeable membrane, a process called osmosis. Eventually the system would reach equilibrium, and the difference in levels would remain constant. The difference in the two levels is related to the osmotic pressure. In fact, one could exert a pressure on the solution side exceeding the osmotic pressure, and solvent molecules could be forced back through the semipermeable membrane into the solvent side. This process is called reverse osmosis and is the basis of the desalination of seawater for drinking purposes. These processes are shown in Figure 13.1. 

Semipermeable Membrane media that allows the passage of solvent molecules but blocks solute molecules Shortwave Radiation radiation emitted by the Sun that passes through and interacts with the atmosphere... 

A reverse osmosis membrane acts as the semipermeable barrier to flow in the RO process, allowing selective passage of a particular species, usually water, while partially or completely retaining other species, ie, solutes such as salts. Chemical potential gradients across the membrane provide the driving forces for solute and solvent transport across the membrane. The solute chemical potential gradient, —A (is, is usually expressed in terms of concentration the water (solvent) chemical potential gradient, — A fiw, is usually expressed in terms of pressure difference across the membrane. 

Water molecules tend to move from a region of higher water concentration to one of lower water concentration. When two different aqueous solutions are separated by a semipermeable membrane (one that allows the passage of water but not solute molecules), water molecules diffusing from the region of higher water concentration to that of lower water concentration produce osmotic pressure (Fig. 2-12). This pressure, n, measured as the force necessary to resist water movement (Fig. 2-12c), is approximated by the van t Hoff equation ... 

How does a semipermeable membrane allow for the passage of water molecules but not any solute ions or molecules ... 

OSMOTIC PRESSURE. Pressure that develops when a pure solvent is separated from a solution by a semipermeable membrane which allows only the solvent molecules to pass through it. The osmotic pressure of the solution is then the excess pressure which must be applied to the solution so as to prevent the passage into it of the solvent through the semipermeable membrane. 

Certain materials, including those that make up the membranes around living cells, are semipermeable. That is, they allow water or other small molecules to pass through, but they block the passage of large solute molecules or ions. When a solution and a pure solvent (or two solutions of different concentration) are separated by the right kind of semipermeable membrane, solvent molecules pass... 

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