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Phase Equilibria
Published in Franco Battaglia, Thomas F. George, Understanding Molecules, 2018
Franco Battaglia, Thomas F. George
The relations (10.46b), (10.49)–(10.52) and (10.56) depend on the nature of the solvent but not on that of the solute: the latter comes into play only in that it determines the solution concentration, namely, only the number of solute molecules is important. Because of this, the properties described by the above relations (vapor-tension lowering, boiling-point elevation, freezing-point depression, osmotic pressure) are called colligative properties. In this regard, we just mention that in case the solute dissociates in solution, evaluating its effects on the colligative properties of the solvent requires that the number of particles dissolved be properly counted, in agreement with the degree of dissociation of the solute.
Measurement of Molecular Weight and Its Distribution
Published in Anil Kumar, Rakesh K. Gupta, Fundamentals of Polymer Engineering, 2018
It is easily observed that dissolving a nonvolatile solute in a liquid results in a depression of the freezing point; that is, the temperature at which a solid phase is formed from solution is lower than the temperature at which the pure solvent freezes. This is the principle at work in an ice cream maker and in snow removal when salt is used to melt and thereby remove snow and ice from roads. Besides lowering the freezing point, the addition of a nonvolatile solute also reduces the vapor pressure at a given temperature, with the consequence that the solution boils at a higher temperature than the pure solvent does. Furthermore, a solution can develop a large osmotic pressure (explained later), which can be measured with relative ease. These four effects—depression of freezing point, elevation of boiling point, lowering of solvent vapor pressure, and development of an osmotic pressure—are called colligativeproperties, and they depend only on the number concentration of the solute in solution in the limit of infinite dilution. Thus, beginning with a known mass of solute, knowledge of any of these colligative properties reveals the total number of molecules in solution, which, in turn, allows for the computation of the number-average molecular weight. However, the relative magnitude of these effects is such that, as the molecular weight of the solute increases and the number of molecules in a given sample mass decreases, not all four colligative properties can be measured with equal accuracy or ease; indeed, membrane osmometry is the method of choice for measuring the number-average molecular weight of high polymers.
Preformulation
Published in Sandeep Nema, John D. Ludwig, Parenteral Medications, 2019
N. Murti Vemuri, Abira Pyne Ramakrishnan
Osmolality is a colligative property. Colligative properties of solutions are properties that depend upon the concentration of undissociated solute molecules and/or ions but not upon the identity of the solute. This ideal solution behavior assumes no specific interactions (e.g., hydrogen bonding) between solute and solvent molecules. Since many solutions are nonideal, or “real solutions,” (resulting from solute–solute and solute–solvent interactions such as dimerization or hydrogen bonding), a direct measurement of properties can give us this measure. Measurable colligative properties include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.
Polyethylene glycol and membrane processes applied to suction control in geotechnical osmotic testing
Published in International Journal of Geotechnical Engineering, 2022
Rick Vandoorne, Petrus J. Gräbe, Gerhard Heymann
Osmotic pressure is a colligative property of a solution and is thus related to the other colligative properties: freezing-point depression, boiling-point elevation and vapour pressure depression (Rudin 1999). Boiling-point elevation and freezing-point depression techniques are not well suited for use with aqueous PEG solutions of high molecular weight as is commonly used in geotechnical osmotic testing. This is because the osmotic pressure of an aqueous PEG solution is temperature dependent (Sweeney and Beuchat 1993; Winzor 2004), which is not the case for many common salt solutions such as NaCl, KCl and CaCl2 (Kiyosawa 2003). Due to their very nature, the freezing-point and boiling-point techniques can only determine the osmotic pressure at the freezing-point and boiling-point temperature respectively. This is likely not within the temperature range of interest for geotechnical osmotic testing. Vapour pressure depression techniques allow the determination of the osmotic pressure at the specific temperature of interest.
Optimization of Water Consumption in Hybrid Evaporative Cooling Air Conditioning Systems for Data Center Cooling Applications
Published in Heat Transfer Engineering, 2019
Theodore A. Ndukaife, A. G. Agwu Nnanna
Salinity was created by dissolving solid sodium chloride in water, and stock solutions of 10 ppt, 20 ppt, and 30 ppt (in the range of brackish water) were obtained and used for the experiment. The results obtained as shown in Figure 7 shows that the salinity of the water used for evaporative cooling did not affect the COP of the system. This is because the presence of the salt in water did not reduce the evaporation rate, and thus the evaporation process proceeds just like in the fresh water case. Therefore the temperature drop experienced by the air as it crosses the cooling pad was the same as in the fresh water case. However, it is expected that over time, there may be an accumulation of salt particles along the pad surfaces and this will ultimately decrease the pads' ability to absorb water and thus reduce pad performance. According to [25], solid sodium chloride dissolves in water with no evidence of a chemical reaction. It is noteworthy to mention that if boiling was required, the salt will act as an impurity and affect the colligative properties (boiling point elevation, freezing point depression) of the solution. However, evaporation takes place at all temperatures and boiling doesn't need to precede evaporation in our case. In addition evaporation only occurs at the surface, in contrast to boiling which occurs throughout the entire volume of the liquid. This means that the salt does not act as an impurity. Our result proves that saline water not fit for drinking was effective for the evaporative cooling process, over the time period the tests were conducted. However, constant use of saline water may also lead to early corrosion of metal parts and may negatively impact the pump.