Solution concentration units

The major goal of this chapter is to help you master the concepts associated with solutions—concentration units, solubility, and especially colligative properties. We will also examine the properties of colloids. If you are still unsure about calculations and the mole concept, review Chapters 1,3, and 4. And again, the only way to master these concepts is to Practice, Practice, Practice. 

In this chapter, you learned about solutions. A solution is a homogeneous mixture composed of a solvent and one or more solutes. Solutions may be unsaturated, saturated, or supersaturated. Solution concentration units include percentage, molarity, molality, and mole fraction. The solubility of solids in liquids normally increases with increasing temperature, but the reverse is true of gases dissolving in liquids. The solubility of gases in liquids increases with increasing pressure. 

The emission spectrometer is interfaced to a programmable calculator (Model 9830, Thermal Printer 9866, Hewlett-Packard, Mississanga, Ontario). During calibration raw millivolt data of the matrix acid blank are subtracted from the standard data. Slopes and intercepts are obtained through a second-order polynomial regression. Dming analysis all data listed on the thermal printer and stored on the %-in. magnetic tape cassettes is in solution concentration units with appropriate sample... 

Table 3.1. Conversion factors for solution concentration units...

Finding out about solutes, solvents, and solutions Working with the different kinds of solution concentration units Checking out the colligative properties of solutions Figuring out colloids... 

But suppose you dissolve 25 grams or 50 grams of sodium chloride in a liter of water Is the solution dilute or concentrated These terms don t hold up very well for most cases. And consider the case of IV solutions — they must have a very precise amount of solute in them, or the patient will be in danger. So you must have a quantitative method to describe the relative amount of solute and solvent in a solution. Such a method exists — solution concentration units. 

You can use a variety of solution concentration units to quantitatively describe the relative amounts of the solute(s) and the solvent. In everyday life, percentage is commonly used. In chemistry, molarity (the moles of solute per liter of solution) is the solution concentration unit of choice. In certain circumstances, though, another unit, molality (the moles of solute per kilogram of solvent), is used. And I use parts-per-million or parts-per-billion when I discuss pollution control. The following sections cover some of these concentration units. 

All of the solution concentration units introduced in this chapter are direct proportionalities. Percentage concentration by mass is a direct proportionality between mass of solute and mass of solution molarity, between moles of solute and liters of solution molality, between moles of solute and kilograms of solvent and normality, between equivalents of solute and liters of solution. These proportional relationships allow you to think of solution concentration units as conversion factors between the two units in the fraction. Do you know mass of solution and need mass of solute Use percentage concentration. Do you know volume of solution and need moles of solute Use molarity. Thinking about solution concentration units in this way allows you to become more skilled at solving quantitative problems. 

Chemists use phenolphthalein in a procedure called a titration, in which they determine the concentration of an acid or base by its reaction with a base or acid of known concentration (see Chapter 10 for info on molarity and other solution concentration units). Here s howto evaluate an acid solution using titration ... 

Solutions in water are designated as aqueous, and the concentration of the solution is expressed in terms of the number of moles of solvent associated with 1 mol of the solute. If no concentration is indicated, the solution is assumed to be dilute. The standard state for a solute in aqueous solution is taken as the hypothetical ideal solution of unit molality (indicated as std. state or ss). In this state... 

Preparing a solution of known concentration is perhaps the most common activity in any analytical lab. The method for measuring out the solute and solvent depend on the desired concentration units, and how exact the solution s concentration needs to be known. Pipets and volumetric flasks are used when a solution s concentration must be exact graduated cylinders, beakers, and reagent bottles suffice when concentrations need only be approximate. Two methods for preparing solutions are described in this section. 

A stock solution is prepared by weighing out an appropriate portion of a pure solid or by measuring out an appropriate volume of a pure liquid and diluting to a known volume. Exactly how this is done depends on the required concentration units. For example, to prepare a solution with a desired molarity you would weigh out an appropriate mass of the reagent, dissolve it in a portion of solvent, and bring to the desired volume. To prepare a solution where the solute s concentration is given as a volume percent, you would measure out an appropriate volume of solute and add sufficient solvent to obtain the desired total volume. 

It is conventional to use molality—moles of solute per kilogram of solvent (symbol m)—as the concentration unit in electrolyte thermodynamics. Accordingly, we shall represent the concentrations of both the indifferent electrolyte and the polymer in these units in this section m3 and m2, respectively. In the same dilute (with respect to polymer) approximation that we have used elsewhere in this chapter, m2 is related to the mass volume system of units C2 by... 

The reduced viscosity expresses the specific viscosity per unit of solute concentration. 

The units of [77] reveal the concentration units in this experiment to be grams of protein per cubic centimer of solution. Dividing this concentration unit by the density of the unsolvated protein converts these concentration units to volume fractions ... 

As noted at the end of the last section, it is fluctuations in concentration 5c2 rather than density which act as the scattering centers of interest for solutions of small molecules. There is nothing in the forgoing theory that prevents us from placing 6p by 6c2, the solute concentration in mass volume" units. Therefore we write for a solution of small molecules... 

The urea solution stream is then fed to the vacuum concentrator unit which operates at 17.3 kPa (130 mm Hg abs) and produces 88.7 wt % urea. It then goes to either two-stage evaporators if prills are made, or a single-stage unit for granule production. 

Concentration. The basis unit of concentration in chemistry is the mole which is the amount of substance that contains as many entities, eg, atoms, molecules, ions, electrons, protons, etc, as there are atoms in 12 g of ie, Avogadro s number = 6.0221367 x 10. Solution concentrations are expressed on either a weight or volume basis. MolaUty is the concentration of a solution in terms of the number of moles of solute per kilogram of solvent. Molarity is the concentration of a solution in terms of the number of moles of solute per Hter of solution. 

Because many studies have shown a direct relationship between pesticide sorption and organic carbon content of sod, attempts have been made to develop a universal sorption coefficient based on sorption of the pesticide to sod organic carbon (44). Sorption based on sod organic carbon is expressed as C, where is pesticide sorbed per unit mass sod organic carbon, and C is pesticide solution concentration after equdibration. If. is the fraction of organic carbon, can be obtained from i in the equation. Assumptions in the use of this approach include... 

Sodium metaborate tetrahydrate can be prepared by cooling a solution containing borax and an amount of sodium hydroxide just in excess of the theoretical amount. The dihydrate is prepared by United States Borax Chemical Corp. by mixing appropriate quantities of borax penta- or decahydrate hydrate and aqueous NaOH to give a 46 to 52% solution concentration of Na20 20 (107). The mixture is then heated to about 90°C to dissolve all soHds and slowly cooled to 60—75°C. Crystals of the dihydrate ate then harvested and dried. 

Evaporative crystalli rs generate supersaturation by removing solvent, thereby increasing solute concentration. These crystallizers may be operated under vacuum, and, ia such circumstances, it is necessary to have a vacuum pump or ejector as a part of the unit. If the boiling poiat elevation of the system is low (that is, the difference between the boiling poiat of a solution ia the crystallizer and the condensation temperature of pure solvent at the system pressure), mechanical recompression of the vapor obtained from solvent evaporation can be used to produce a heat source to drive the operation. 

II The increment in the free energy, AF, in the reaction of forming the given substance in its standard state from its elements in their standard states. The standard states are for a gas, fugacity (approximately equal to the pressure) of 1 atm for a pure liquid or solid, the substance at a pressure of 1 atm for a substance in aqueous solution, the hyj)othetical solution of unit molahty, which has all the properties of the infinitely dilute solution except the property of concentration. 

The response of solute concentration in the raffinate to the sol-vent-to-feed ratio S /F can be calculated by Eqs. (15-26) and (15-27) for a constant number of transfer units based on the overall raffinate phase N r-... 

The values given in this table are only approximate, but they are adequate for process screening purposes with Eqs. (16-24) and (16-25). Rigorous calculations generally require that activity coefficients be accounted for. However, for the exchange between ions of the same valence at solution concentrations of 0.1 N or less, or between any ions at 0.01 N or less, the solution-phase activity coefficients prorated to unit valence will be similar enough that they can be omitted. 

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