Vapor pressure depression

A wide variety of data for mean ionic activity coefficients, osmotic coefficients, vapor pressure depression, and vapor-liquid equilibrium of binary and ternary electrolyte systems have been correlated successfully by the local composition model. Some results are shown in Table 1 to Table 10 and Figure 3 to Figure 7. In each case, the chemical equilibrium between the species has been ignored. That is, complete dissociation of strong electrolytes has been assumed. This assumption is not required by the local composition model but has been made here in order to simplify the systems treated. 

In the present study, systems composed of two solvents and a salt are treated as ternary systems. Data on the vapor pressure depression of the solvent by the salt for isothermal systems and on the boiling point elevation of the solvent in the presence of salt for isobaric systems are used to develop the parameters for the solvent-salt binaries. For such binaries only the activity coefficients for the solvent are considered. The parameters for all three binary sets are generated from the binary data by a regression subroutine. 

Fig. 9.8. Apparatus for the determination of molecular weights by vapor-pressure depression. The bottom of the differential manometer (D) may he frozen with Dry Ice to keep the mercury from sloshing when solvent is added or removed, or when the sample tube is attached. The solenoid used to stir the sample tube is described in Fig. 9.6. V and V are grease-free valves.

The isopiestic (isothermal distillation) method for the determination of molecular weights is closely related to the vapor pressure depression method.10 A weighed amount of standard is introduced into one leg of an apparatus and a weighed portion of the unknown is placed in the other leg. Solvent is introduced into the apparatus, which is then evacuated and thermostated. The solvent will distill from one solution to the other until the vapor pressures (and therefore mole fractions) of the two have equalized. If the solutions are ideal, or if the deviations from ideality are similar, equilibrium will occur when the mole fraction of the known equals that of the unknown. 

The observation of alkyl cations such as the ferf-butyl cation [trimethyl-carbenium ion, (CH3)3C+] 1 and the isopropyl cation [dimethylcarbenium ion, (CH3)2CH+] 2 was a long-standing challenge. The existence of alkyl cations in systems containing alkyl halides and Lewis acids has been inferred from a variety of observations, such as vapor pressure depressions of CH3C1 and C2H5CI in the... 

Vapor pressure depression = AP = (v.p. solvent) x (mole fraction solute)... 

The LCM has proven to be useful in predicting data of molal ionic activity coefficients and vapor pressure depression of various single electrolyte, single solvent systems. The standard deviation of the natural logarithm of the mean activity coefficient was 0.01 for uni-univalent aqueous single electrolytes (17). Similar results... 

There are many measurement techniques for activity coefficients. These include measuring the colligative property (osmotic coefficients) relationship, the junction potentials, the freezing point depression, or deviations from ideal solution theory of only one electrolyte. The osmotic coefficient method presented here can be used to determine activity coefficients of a 1 1 electrolyte in water. A vapor pressure osmometer (i.e., dew point osmometer) measures vapor pressure depression. 

Add the appropriate boxes and connectors to Figure 12.10 to illustrate the calculation of mole-related quantities from (a) vapor-pressure depression data, (b) freezing-point lowering data, (c) boiling-point elevation data, and (d) osmotic pressure data. 

Calculate the vapor-pressure depression of an aqueous solution of density 1.02 g/mL if its osmotic pressure at 25°C is 98.0 torr. The molar mass of the nonvolatile solute is 125 g/mol. 

Saturated salt solutions and sulfuric acid solutions establish relative humidity by reducing the vapor pressure above an aqueous solution (a colligative effect). Saturated salt solutions at controlled temperature maintain a constant relative humidity as long as excess salt and bulk solution are present. As water is added or removed from the solution, moisture from the head-space will either condense or evaporate (as appropriate), with subsequent dissolution or precipitation of salt to maintain the equilibrium vapor pressure. Because the degree of vapor pressure depression is dependent on the number of species in solution and, further, since the solubility of most salts is somewhat dependent on temperature, the relative humidity generated is also temperature dependent. Hence, use of the same salt at different temperatures can result in different relative humidities. Refs. can be consulted for specific saturated salt solutions that result in defined relative humidities as a function of... 

By comparing the weight of the aerogel at 0 and 30 % relative humidity the amount of water that each RF aerogel adsorbs is determined. After storing the samples at 90 °C for 48 h and cooling down to room temperature in dry N2-atmosphere the weight at 0 % relative humidity is measured. To obtain the values at 30 % relative humidity the samples are placed in a closed cell with a specific salt-water solution. By vapor pressure depression above saturated solutions this specific solution keeps the atmosphere constant at 30 % relative humidity. 

Aerothene [Dow]. TM for a group of chlorinated solvents used as vapor pressure depressants, or with compressed gases to replace fluorocarbon propellant systems. 

Use Cold cleaning, vapor degreasing, resins application, dry-film photoresist processing, adhesive solvent, in aerosols as solvent and vapor-pressure depressant. 

Osmolality is commonly measured by freezing point or vapor pressure depression. In terms of vapor pressure (P ), the osmotic pressure (jt) is defined as... 

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