Exploring Water Mixtures

Students mix the five unknown solids with a greater amount of water than they used in Lesson 4. Through observations and discussion, students discover another property of the solids some dissolve in water to form solutions, while others form suspensions. Through the process of filtering mixtures, students discover that solids in a suspension can be separated while those in a solution cannot. (In the next lesson, they will examine how to separate the solids in a solution through the process of evaporation.) 

In this lesson, students begin to investigate two types of mixtures solutions and suspensions. A solution is a homogeneous mixture. Its components are uniformly mixed therefore, you cannot see the parts that compose it. Solutions tend to be clear. For example, when you mix sugar with water, you create a solution. The sugar, which is the dissolved substance, is called the solute, and the water is called the solvent. 

In this lesson, students gradually add small amounts of each unknown to a fixed amount of water. As students add more and more of some of the unknowns, the mixtures will reach a point at which no more of these unknowns will dissolve. When the water can hold no more of an unknown, it is said to be a saturated solution. Students will observe that some of each unknown is dissolved and some remains visible in the water. The remaining, or undissolved unknown is said to be suspended in the water. 

A suspension is a heterogeneous mixture. Since its components are not uniformly mixed throughout, they can easily be seen. Suspensions are cloudy. For example, when you mix cornstarch with water, you create a suspension. 

You can separate some suspensions simply by allowing them to remain undisturbed. The force of gravity causes the heavier material in the suspension to settle slowly to the bottom of the container. For example, think about salad 

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The heats of solution and dilution of electrolytes in nonaqueous-aqueous solvent mixtures have been limited mostly to alcohol-water systems and a few measurements in dimethylsulfoxide-water and dioxane-water mixtures (J, 2). The structural maximum in aqueous-organic solvents at high water content has been well established by a variety of techniques (3,4), but few systems have been explored over the whole composition range. 

Questions of general catalysis by the various acidic species present in strongly acid media such as sulfuric acid-water mixtures are beginning to be explored.134... 

Lowry and Johnson (43) explored the efficiency of dechlorination of dissolved PCBs by Fe° (particle size = < 150,000 nm) and Fe p> (particle size = 30 to 50 nm) particles in water/methanol solutions. With commercial Fe , no PCB dechlorination was observed even after 180 days, suggesting that this form of iron is not reactive. On the other hand, Fe p) resulted in effective dechlorination of PCBs within 45 days. Wang and Zhang (34) also studied the dechlorination of PCBs in an ethanol-water mixture under ambient conditions using Fe p> and Pd coated Fe p). Over a 17 h experiment, partial degradation ( 25%) of PCB to biphenyl was observed with Fef P) while Pd/Fe resulted in complete dechlorination. 

D19. Many extraction systems are partially miscible at high concentrations of solute, but close to immiscible at low solute concentrations. At relatively low solute concentrations both the McCabe-Thiele and trianglar diagram analyses are applicable. This problem explores this. We wish to use chloroform to extract acetone from water. Equilibrium data are given in Table 13-4. Find the number of equilibrium stages required for a countercurrent cascade if we have a feed of 1000.0 kg/h of a 10.0 wt % acetone, 90.0 wt % water mixture. The solvent used is chloroform saturated with water (no acetone). Flow rate of stream Eq = 1371 k. We desire an outlet raffinate concentration of 0.50 wt % acetone. Assume immiscibility and use a weight ratio units graphical analysis. Conpare results with Problem 13.D43. 

The presence of a solute affects the physical properties of the solvent. For instance, when salt is spread on icy sidewalks, a mixture is created with a lower freezing point than that of pure water and the ice melts. In this part of the chapter we explore the molecular nature of these effects and see how to treat them quantitatively. 

The most explored solvent systems are based on water-alcohol mixtures, acetonitrile-water and DMSO-water [8], Where possible, methanol is the solvent of choice, because its general effect on pKjS has been studied so extensively. It is thought to be the least error-prone of the common solvents [28]. 

About one decade ago Bass et al. [13,14] proposed first that such approach could help in exploring the structure of water dissolved silicates. Following this initiative, recently we critically evaluated how the published FTIR and Raman assignments could be adopted for differentiating between the molecular structures of some commercially available sodium silicate solutions [7-9,15], In this paper we present comparative structural studies on aqueous lithium and potassium silicate solutions as well. According to some NMR studies, the nature of A+ alkaline ion and the A+/Si ratio barely affects the structural composition of dissolved silicate molecules [5], In contrast, various empirical observations like the tendency of K-silicate solutions to be less tacky and more viscous than their Na-silicate counterparts, the low solubility of silica films obtained from Li-silicate solutions compared to those made from other alkaline silicate solutions, or the dependence of some zeolite structures on the nature of A+ ions in the synthesis mixture hint on likely structural differences [16,17]. It will be shown that vibrational spectroscopy can indeed detect such differences. 

The construction of a diazaadamantane skeleton under microwave conditions has been explored by Ivachtchenko and colleagues (Scheme 2.273) [462], Cleavage of semi-natural tetrahydro-(-) -cytisine in acidic methanol provided the corresponding free diamine ester, which was used directly in the next step without purification. Thus, l,T-carbonyldiimidazole (CDI) in a water/methanol mixture was added at... 

PHEMA solubility decreases with increasing ion concentration. As a result, Mikos et al. used salt solutions of varying ionic strength to dilute the reaction mixtures (Liu et al., 2000). It was noted that increasing the ion content of the aqueous solution to 0.7M, interconnected macropores were obtained at 60 vol% water. Surfactants may also be used to control the network pore structure. However, not much work has been done in this area, since surfactants typically work to reduce the surface repulsions between the two phases and form a uniform emulsion. These smaller emulsion droplets when gelled will create a network with an even smaller porous structure. Yet, this is still a promising area of exploration, since it may be possible to form alternate phase structures such as bicontinuous phases, which would be ideal for cellular invasion. 

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