Nonvolatile solutes in water

Consider a 1.00 m solution and a 2.00 m solution of glucose, C6H12O6, a nonvolatile solute, in water, (a) Which solution has the greater boiling-point elevation (b) Which one has the higher boiling point ... 

For a solution of one (nonvolatile) solute in water, whose water activity is known over a concentration range, the activity of the solute can be derived from the Gibbs-Duhem relation, which can for this case be written... 

How does increasing the concentration of a nonvolatile solute in water affect the following properties (a) vapor pressure,... 

A solution of a nonvolatile solute in water has a boiling point of 375.3 K. Calculate the vapor pressure of water above this solution at 338 K. The vapor pressure of pure water at this temperature is 0.2467 atm. 

Sucrose is a nonvolatile, nonionizing solute in water. Determine the vapor pressure lowering, at 25°C, of the 1.25 sucrose solution in Example 14-2. Assume that the solution behaves ideally. The vapor pressure of pure water at 25°C is 23.8 torr (Appendix E). 

The presence of a nonvolatile. solute in an aqueous solution tends to reduce its water vapor pressure to an extent that depends on the nature and concentration of the solute. On a purely geometric basis, there are fewer solvent molecules in the surface layer than in the case of a pure solvent drop. This would lead to a vapor pressure reduction proponional to concentration, and this is observed for ideal soiiitiotts. Specific chemical effects of an attractive nature between solute and solvent may lead to a further reduction in vapor pressure. The reduction of vapor pressure makes it possible for aero.sol particles to incorporate significant amounts of aqueous. solution in equilibrium with air whose relative humidity is much less than 100%. The water associated with aerosol particles strongly affects light... 

In cases in which there is a nonvolatile solute in a solvent (for example, salt in water) it is not possible to sublime the solution into the left-hand chamber (shown in Fig. 5.6), and oxygen removal is best accomplished by carrying out the freeze-pump-thaw cycle in situ before filling. Again, it is necessary to add a magnetic-stirrer bar to the bottom of the compartment to ensure that a representative sample of the mixture is drawn up into the capillary. 

Automotive antifreeze contains ethylene glycol, CH2(OH)CH2(OH), a nonvolatile nonelectrolyte, in water. Calculate the boiling point and freezing point of a 25.0% by mass solution of ethylene glycol in water. 

Generalizations. Several generalizations can be made regarding taste (16,26). A substance must be in water solution, eg, the Hquid bathing the tongue (sahva), to have taste. Water solubiUty is the first requirement of the taste stimulus (12). The typical stimuli are concentrated aqueous solution in contrast with the Hpid-soluble substances which act as stimuli for olfaction (22). Many taste substances are hydrophilic, nonvolatile molecules (15). Taste detection thresholds for lipophilic molecules tend to be lower than those of their hydrophilic counterparts (16). 

Toxicity. Sodium fluoroacetate is one of the most effective all-purpose rodenticides known (18). It is highly toxic to all species of rats tested and can be used either in water solution or in bait preparations. Its absence of objectionable taste and odor and its delayed effects lead to its excellent acceptance by rodents. It is nonvolatile, chemically stable, and not toxic or irritating to the unbroken skin of workers. Rats do not appear to develop any significant tolerance to this compound from nonlethal doses. However, it is extremely dangerous to humans, to common household pets, and to farm animals, and should only be used by experienced personnel. The rodent carcasses should be collected and destroyed since they remain poisonous for a long period of time to any animal that eats them. 

FIGURE 8.28 The vapor pressure of a solvent is lowered by a nonvolatile solute. The barometer tube on the left has a small volume of pure water floating on the mercury. That on the right has a small volume of 10 m NaCI(aq) and a lower vapor pressure. Note that the column on the right is depressed less by the vapor in the space above the mercury than the one on the left, showing that the vapor pressure is lower when solute is present. 

Equation describes the total vapor pressure above a solution when the solute does not have a significant vapor pressure of its own. In other words, Raoulfs law applies only to nonvolatile solutes. When the solute is volatile, such as for a solution of acetone in water, the total vapor pressure above the solution is a sum of contributions from both solvent and solute. 

The phase diagram for water, showing how the phase boundaries change when a nonvolatile solute dissolves in the liquid. 

The depression of the freezing point of a solvent due to the presence of a dissolved solute is an example of a colligative property, that is, a property of a dilute solution that depends on the number of dissolved particles and not on the identity of the particles. Water has a freezing point depression constant, Kf, of 1.86 K kg mol-1. In other words, for every mole of nonvolatile solute dissolved in a kilogram of water, the freezing point of water is lowered by 1.86°C. The change in freezing point, A T, can be calculated from the equation... 

The curves in Fig. 10 were drawn for the particular instance of a volatile solute dissolved in a volatile solvent, such as would exist for the acetone-chloroform system (whose diagram is very nearly like that of Fig. 10B). For many nonvolatile solutes, it not possible to trace smooth partial pressure curves across the entire range of mole fractions. This is especially true for aqueous salt solutions, where at a certain concentration of solute the solution becomes saturated. Any further addition of crystalline solute to the system does not change the mole fraction in the liquid phase, and the partial pressure of water thereafter remains constant, in accord with the phase rule. This phenomenon permits the use of saturated salt solutions as media to establish fixed relative humidity values in closed systems [12],... 

There are several basic physical-chemical principles involved in the ability of aerosol particles to act as CCN and hence lead to cloud formation. These are the Kelvin effect (increased vapor pressure over a curved surface) and the lowering of vapor pressure of a solvent by a nonvolatile solute (one of the colligative properties). In Box 14.2, we briefly review these and then apply them to the development of the well-known Kohler curves that determine which particles will grow into cloud droplets by condensation of water vapor and which will not. 

Thus, if a nonvolatile solute is dissolved in water, the vapor pressure of water is lowered by an amount proportional to the mole fraction of dissolved solute, taking into account any dissociation that occurs (vide infra). It should be noted that this assumes ideal solution behavior. 

As shown in the first diagram in this sidebar (for water), the melting point of solution is also displaced toward lower values by addition of a nonvolatile solute, the freezing-point depression effect. By arguments similar to those given above, the freezing-point depression ATfp = T p — 7fp(.xB) will also be found to be proportional to solute molality ... 

What is the vapor pressure (in mm Hg) of the following solutions, each of which contains a nonvolatile solute The vapor pressure of water at 45.0°C is 71.93 mm Hg. 

Certain of the nonvolatile compounds affected the ability of panelists to determine the threshold of d-limonene (Table V). Thus, precision appeared high in solutions of water and in the aqueous solutions of sugar alone, but was less in solutions containing pectin and least in solutions containing acid. 

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