Phase diagram salt/water

Using the phase diagram for water and Raoult s law, explain why salt is spread on the roads in winter (even when the temperature is below freezing). 

Figure 1. Solid-liquid phase diagrams for water — (n-C4H9)i+N00CR systems.The number attached to each curve stands for the same salt as the one listed in TABLE I. The congruent composition corresponds to the hydrate with hydration number 30.

Figure 4.71 Phase diagrams of water-carboxymethylcell-ulose (CMC) sodium salt. Water content (WJ = mass of water/mass of dry CMC, (gg ) heating rate, 10°Cmin sample mass, ca 5 mg sample vessel, sealed-type aluminum...

Fig. 5. Stable phase diagram of the quaternary system (NaCl - KCl - Na2B4C>7 - K2B4O7 - H2O) at 298.15 K. (a), dry-salt phase diagram (b), water-phase diagram.

Hydrated salts are the intermediate compounds of water-salt systems. Some hydrated salts (such as CaCl2.6H20, CaCNOs) 6H2O) are good materials for heat storage, and many hydrated double salts(such as alum) are industrial products. The computerized prediction of the formation and stability of hydrated salts and hydrated double salts is crucial for the computerized prediction and assessment of the phase diagrams of water-salt systems. 

The basis for the separation is that when two polymers, or a polymer and certain salts, are mixed together in water, they are incompatible, leading to the formation of two immiscible but predominantly aqueous phases, each rich in only one of the two components [Albertsson, op. cit. Kula, in Cooney and Humphrey (eds.), op. cit., pp. 451 71]. A phase diagram for a polyethylene glycol (PEG)-Dextran, two-phase system is shown in Fig. 22-85. Proteins are known to distribute unevenly between these phases. This uneven distribution can be used for the selective concentration and partial purification of the products. Partitioning between the two phases is controlled by the polymer molecular weight and concentration, protein net charge and... 

HF is miscible with water in all proportions and the phase diagram (Fig. 17.4a) shows the presence of three compounds H2O.HF (mp — 35.5°), H2O.2HF (mp-75.5°) and H2O.4HF (mp — 100.4°, i.e. 17° below the mp of pure HF). Recent X-ray studies have confirmed earlier conjectures that these compounds are best formulated as H-bonded oxonium salts [HsOJF, [H30][HF2], and [H30][H3F4] with three very strong H bonds per oxonium ion and average O - - F distances of 246.7, 250.2... 

Figure 104. Phase separation of a salt hydrate (e.g. CaCl2 6H20) into three distinct phases with different water concentration and density (right) and corresponding phase diagram (left)...

The use of dissociable diastereomers for enantiomer resolution may be illustrated by the case where racemic mandelic acid is resolved using en-antiomerically pure a-methylbenzylamine. The n and p salts of a-methylbenzyl-amine mandelate have aqueous solubilities of 49.1 and 180 g/L, respectively, at 25°C [153], A more recent example, which focuses on the crystallographic origin of the solubility differences, is provided by the resolution of ( )-mandelic acid with (-)-ephedrine in water or methanol solution [154], In general, the relative solubilities of the n and p salt pairs are strongly influenced by the choice of solvent medium and temperature, which provide considerable flexiblity in optimizing the crystallization conditions and the efficiency of resolution. This process may be facilitated by the development of a full solubility phase diagram. 

SLE of quaternary ammonium ILs in alcohols, hydrocarbons, and water have been measured for many salts. Systematic studies of SLE phase diagrams for quaternary ammonium salts [(Cj)2C2HOC2N]Br, [(Ci)2C3HOC2N]Br, [(Cj)2C4HOC2N]Br, and [(Ci)2CgHOC2N]Br in water and alcohols have been published [52,79]. Other anions including [BFJ, [PFg], [dca] , and [TfjN] have also been investigated [53]. 

The interesting influence of the cation on the SLE diagram IL + water can be observed [99,100] from the diagrams of ammonium salts [(Cio)2(Q)2N][N03] and [Be(Ci)2C N][N03]. Simple liquidus curve and no immiscibility in the liquid phase for the didecyldimethylammonium cation with the eutectic point shifted strongly to the solvent-rich side was noted (see Figure 1.11). 

Diphasic liquid systems used in CCC may have a wide variety of polarities. The most polar systems are the ATPS made by two aqueous-liquid phases, one containing a polymer, for example, polyethylene glycol (PEG), the other one being a salt solution, for example, sodium hydrogen phosphate. The less polar systems do not contain water there can be two-solvent systems, such as heptane/acetonitrile or dimethylsulfoxide/hexane systems or mixtures of three or more solvents. Intermediate polarity systems are countless since any proportion of three or more solvents can be mixed. Ternary phase diagrams are used when three solvents are mixed together. 

The IL is mainly located in the upper phases of the ATPS. The lower phases contain the phosphate salt. Water is partitioning almost evenly between the two-liquid phases. By definition, all initial compositions belonging to the same tie-line split into two liquid phases of identical composition only the volume amounts (and the phase ratios) change. Since the tie-lines are, by chance, almost parallel to the water hypotenuse, the phase diagram clearly shows that the chemical composition of the two liquid phases crucially depends on the water content of the system. 

Lower a small crystal of Glauber salt into the solution. Explain what happens. Draw curves of the solubility of anhydrous sodium sulphate and its crystallohydrates. Acquaint yourself with the phase diagram of the sodium sulphate-water system. In what parts of the diagram is the system invariant, monovariant, or divariant ... 

It is also good practice to have each salt s phase-diagram, in order to know how they would precipitate under supercritical conditions. For example, sodium chloride yields crystals that are larger than sodium sulphate [28], which facilitates its separation by filtration or using cyclones. When a sodium chloride solution is heated, it reaches an L/V equilibrium zone, where water-evaporation takes place, and the salt s concentration in the liquid drops, thus producing formation of larger crystals (10 tolOO (am). In contrast, sodium sulphate reaches... 

Fujiwara, M., T. Okano, H. Amano, H. Asano, and K. Ohbu. 1997. Phase diagram of a-sulfonated palmitic acid methyl ester sodium salt-water systdrangmuirl 3 3345-3348. 

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