Dilution The process of adding solvent

Dilution the process of adding solvent to lower the concentration of solute in a solution. (4.3)... 

The process of adding water to a solution is called dilution. Because only the solvent amount is changing, only the total volume and molarity of the solution is changing, not the number of moles of solute. Modifying the molarity equation yields... 

Dilution The process of reducing the concentration of a solute in solution, usually simply by adding more solvent. 

To save time and space in the laboratory, solutions that are routinely used are often purchased or prepared in concentrated form (called stock solutions). Water (or another solvent) is then added to achieve the molarity desired for a particular solution. The process of adding more solvent to a solution is called dilution. For example, the common laboratory acids are purchased as concentrated solutions and diluted with water as they are needed. A typical dilution calculation involves determining how much water must be added to an amount of stock solution to achieve a solution of the desired concentration. The key to doing these calculations is to remember that only water is added in the dilution. The amount of solute in the final, more dilute, solution is the same as the amount of solute in the original concentrated stock solution. 

One of the most common procedures encountered in any science laboratory is dilution, the process in which solvent is added to a solution to decrease the concentration of the solute. In dilution, the amount of solute does not change. The number of moles of solute is the same before and after dilution. Because we already know that the number of moles of solute equals the product of molarity and volume, we can write the following equation, where the subscripts denote the initial (i) and final (f) values of the quantities involved ... 

Reverse Osmosis. Osmosis is the flow of solvent through a semipermeable membrane, from a dilute solution to a concentrated solution. This flow results from the driving force created by the difference in pressure between the two solutions. Osmotic pressure is the pressure that must be added to the concentrated solution side to stop the solvent flow through the membrane. Reverse osmosis is the process of reversing the flow, forcing water through a membrane from a concentrated solution to a dilute solution to produce pure water. Figure 2 illustrates the processes of osmosis and reverse osmosis. 

This reaction, in general, competes, more or less effectively, with simple protonation, and is favoured when the hydrocarbon is added as a solid. With care, if dissolution is effected by extraction or as a dilute solution in an inert but miscible solvent such as acetic acid, only protonation results (Grace and Symons, 1959). It therefore appears that oxidation is facilitated during the process of dissolution of the pure hydrocarbon, and this has been explained (Carrington ef al., 1959) in terms of an initial charge transfer between protonated and unprotonated species ... 

In very dilute solutions, the molecules of the solute are completely separated from each other and are in contact only with solvent molecules. If more solvent is added to such a solution, the number of solute-solvent contacts does not change. Hence no enthalpy change accompanies this process. Solute molecules occupying some location exclude this location from the volume available to other molecules. This steric interference influences entropy but not enthalpy [7]. 

SECTION 4.5 The concentration of a solution expresses the amount of a solute dissolved in the solution. One of the common ways to express the concentration of a solute is in terms of molarity. The molarity of a solution is the number of moles of solute per liter of solution. Molarity makes it possible to interconvert solution volume and number of moles of solute. Solutions of known molarity can be formed either by weighing out the solute and diluting it to a known volume or by the diution of a more concentrated solution of known concentration (a stock solution). Adding solvent to the solution (the process of dilution) decreases the concentration of the solute without changing the number of moles of solute in the solution... 

The principle of solvent extraction in refining is as follows when a dilute aqueous metal solution is contacted with a suitable extractant, often an amine or oxime, dissolved in a water-immiscible organic solvent, the metal ion is complexed by the extractant and becomes preferentially soluble in the organic phase. The organic and aqueous phases are then separated. By adding another aqueous component, the metal ions can be stripped back into the aqueous phase and hence recovered. Upon the identification of suitable extractants, and using a multistage process, solvent extraction can be used to extract individual metals from a mixture. 

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