Matter Up Solutions

A solution is a homogeneous mixture, meaning that it is the same throughout. If you dissolve sugar in water and mix it really well, for example, your mixture is basically the same no matter where you sample It. 

A solution is composed of a solvent and one or more solutes. The solvent Is the substance that s present in the largest amount, and the solute Is the substance that s present in the lesser amount. These definitions work most of the time, but there are a few cases of extremely soluble salts, such as lithium chloride, in which more than 5 grams of salt can be dissolved in 5 milliliters of water. However, water is still considered the solvent, because it s the species that has not changed state. In addition, there can be more than one solute in a solution. You can dissolve salt in water to make a brine solution, and then you can dissolve some sugar in the same solution. You then have two solutes, salt and sugar, but you still have only one solvent — water. 

When I talk about solutions, most people think of liquids. But there can also be solutions of gases. Our atmosphere, for example, is a solution. Because air is almost 79 percent nitrogen, it s considered the solvent, and the oxygen, carbon dioxide, and other gases are considered the solutes. There are also solid solutions. Alloys, for example, are solutions of one metal in another metal. Brass is a solution of zinc in copper. 

Why do some things dissolve in one solvent and not another For example, oil and water will not mix to form a solution, but oil will dissolve in gasoline. There s a general rule of solubility that says like-dissolves-like in regards to polarity of both the solvent and solutes. Water, for example, is a polar material it s composed of polar covalent bonds with a positive and negative end of the molecule. (For a rousing discussion of water and its polar covalent bonds, see Chapter 7.) Water will dissolve polar solutes, such as salts and alcohols. Oil, however, is composed of largely nonpolar bonds. So water will not act as a suitable solvent for oil. 

A saturated solution contains the maximum amount of dissolved solute possible at a given temperature. If it has less than this amount, it s called an unsaturated solution. Sometimes, under unusual circumstances, the solvent may actually dissolve more than its maximum amount and become supersaturated. This supersaturated solution is unstable, though, and sooner or later solute will precipitate (form a solid) until the saturation point has been reached. 

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The visible crystals that develop during a crystallization procedure are built up as a result of growth either on nuclei of the material itself or surfaces of foreign material serving the same purpose. Neglecting for the moment the matter of impurities, nucleation theory provides an explanation for certain qualitative observations in the case of solutions. 

Carbon disulphide should never be used if any alternative solvent is available, as it has a dangerously low flash-point, and its vapours form exceedingly explosive mixtures with air. Ether as a solvent for recrystallisation is much safer than carbon disulphide, but again should be avoided whenever possible, partly on account of the danger of fires, and partly because the filtered solution tends to creep up the walls of the containing vessel and there deposit solid matter by complete evaporation instead of preferential crystallisation. 

B. Aminolhymol.—The crude, wet nitrosothymol so obtained is worked up with a mixture of 900 cc. of 28 per cent ammonia water (sp. g. 0.90) and 1600 cc. of water the brown solution is filtered free of a little resinous matter, and hydrogen sulfide is passed into it. The brown color disappears and a white precipitate of aminothymol forms. The passage of hydrogen sulfide is continued for thirty minutes longer (Note 3), when the base is filtered and washed well with cold water, contact with air being avoided as far as possible (Note 4). 

If our inspection process has pointed out areas in need of housekeeping, and these same areas continually show up on our inspection, an adjustment would appear to be in order. One possible solution would be to spend more time and effort on housekeeping issues. However, no matter how much time and effort we spend on housekeeping, we can usually find places lacking in housekeeping. Possibly there is no money, time, equipment, or other resources available to perform housekeeping activities at this time. 

The molecular mechanics calculations discussed so far have been concerned with predictions of the possible equilibrium geometries of molecules in vacuo and at OK. Because of the classical treatment, there is no zero-point energy (which is a pure quantum-mechanical effect), and so the molecules are completely at rest at 0 K. There are therefore two problems that I have carefully avoided. First of all, I have not treated dynamical processes. Neither have I mentioned the effect of temperature, and for that matter, how do molecules know the temperature Secondly, very few scientists are interested in isolated molecules in the gas phase. Chemical reactions usually take place in solution and so we should ask how to tackle the solvent. We will pick up these problems in future chapters. 

Bromo-2 -(3"-dimethylaminopropyl)-amino4 potassium carbonate (5 g) and copper powder (0.4 g). It is then heated under reflux for 4B hours, cooled, and the insoluble matter filtered off. After washing with dimethylformamide (20 cc), the filtrate is taken up in distilled water (200 cc). The base formed is extracted with ether (3 times with 50 cc), the ethereal solution is dried over sodium sulfate, the ether driven off on a water-bath and the residue distilled. In this way there is obtained 3ethereal hydrogen chloride on the base dissolved in acetone this hydrochloride melts at 180°C. 

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