Solubility tests water

An indication whether a water-insoluble compound is an acid or a phenol (or enol) will be obtained from the Solubility Tests water-soluble acids will liberate carbon dioxide from 5 per cent, sodium bicarbonate solution (see Section III,85,(i). ... 

In the standard method, the metal enclosure (called the air chamber) used to hold the hydrocarbon vapors is immersed in water before the test, then drained but not dried. This mode of operation, often designated as the wet bomb" is stipulated for all materials that are exclusively petroleum. But if the fuels contain alcohols or other organic products soluble in water, the apparatus must be dried in order that the vapors are not absorbed by the water on the walls. This technique is called the dry bomb" it results in RVP values higher by about 100 mbar for some oxygenated motor fuels. When examining the numerical results, it is thus important to know the technique employed. In any case, the dry bomb method is preferred. 

Boron trioxide is not particularly soluble in water but it slowly dissolves to form both dioxo(HB02)(meta) and trioxo(H3B03) (ortho) boric acids. It is a dimorphous oxide and exists as either a glassy or a crystalline solid. Boron trioxide is an acidic oxide and combines with metal oxides and hydroxides to form borates, some of which have characteristic colours—a fact utilised in analysis as the "borax bead test , cf alumina p. 150. Boric acid. H3BO3. properly called trioxoboric acid, may be prepared by adding excess hydrochloric or sulphuric acid to a hot saturated solution of borax, sodium heptaoxotetraborate, Na2B407, when the only moderately soluble boric acid separates as white flaky crystals on cooling. Boric acid is a very weak monobasic acid it is, in fact, a Lewis acid since its acidity is due to an initial acceptance of a lone pair of electrons from water rather than direct proton donation as in the case of Lowry-Bronsted acids, i.e. 

The oxime is freely soluble in water and in most organic liquids. Recrystallise the crude dry product from a minimum of 60-80 petrol or (less suitably) cyclohexane for this purpose first determine approximately, by means of a small-scale test-tube experiment, the minimum proportion of the hot solvent required to dissolve the oxime from about 0-5 g. of the crude material. Then place the bulk of the crude product in a small (100 ml.) round-bottomed or conical flask fitted with a reflux water-condenser, add the required amount of the solvent and boil the mixture on a water-bath. Then turn out the gas, and quickly filter the hot mixture through a fluted filter-paper into a conical flask the sodium chloride remains on the filter, whilst the filtrate on cooling in ice-water deposits the acetoxime as colourless crystals. These, when filtered anddried (either by pressing between drying-paper or by placing in an atmospheric desiccator) have m.p. 60 . Acetoxime sublimes rather readily when exposed to the air, and rapidly when warmed or when placed in a vacuum. Hence the necessity for an atmospheric desiccator for drying purposes. 

Test its solubility in water and compare the result with that in (i). 

Group I. This includes the lower members of the various homologous series (4-5 atoms in a normal chain) that contain oxygen and/or nitrogen in their structures they are soluble iu water because of their low carbon content. If the compound is soluble in both water and ether, it would also be soluble in other solvents so that further solubility tests are generally unnecessary the test with sodium bicarbonate solution should, however, be performed (see Section XI,6). 

Solubility in water. Treat a 0 10 g. portion of the solid with successive 10 ml. portions of water, shaking vigorously after each addition, until 3 0 ml. have been added. If the compound does not dissolve completely in 3 0 ml. of water, it may be regarded as insoluble in water. When dealing with a liquid, add 0 -20 ml. of the compound to 3 0 ml. of water and shake. In either case, test the contents of the small test-tube with htmus (or with Universal indicator paper) it is best to remove a little of the solution or supernatant liquid with a dropper. 

Solubility in ether. Use 0 -10 g. of solid or 0 -20 ml. of a liquid in a dry test-tube and proceed exactly as in testing the solubility in water, but do not employ more than 3 0 ml. of solvent. 

Solubility in 5 per cent, hydrochloric acid. Add the acid to 0 10 g. of the solid or 0 20 ml. of the liquid in quantities of 1 0 ml. until 3 0 ml. have been introduced. Some organic bases (e.g., p-naphthylamine) form hydrochlorides that are soluble in water but are precipitated by an excess of acid if solution occurs at any time, the unknown is assigned to Group IV. If the compound appears insoluble, remove some of the supernatant liquid by means of a dropper to a semimicro test-tube (75 X 10 mm.), and add 5 per cent, sodium hydroxide solution until basic and observe whether any precipitate is produced the formation of a precipitate will place the compound in Group IV. 

Alkali or alkaline-earth salts of both complexes are soluble in water (except for Ba2[Fe(CN)g]) but are insoluble in alcohol. The salts of hexakiscyanoferrate(4—) are yellow and those of hexakiscyanoferrate(3—) are mby red. A large variety of complexes arise when one or more cations of the alkah or alkaline-earth salts is replaced by a complex cation, a representative metal, or a transition metal. Many salts have commercial appHcations, although the majority of industrial production of iron cyanide complexes is of iron blues such as Pmssian Blue, used as pigments (see Pigments, inorganic). Many transition-metal salts of [Fe(CN)g] have characteristic colors. Addition of [Fe(CN)g] to an unknown metal salt solution has been used as a quaUtative test for those transition metals. 

Aquatic Toxicity. The standard tests to measure the effect of substances on the aquatic environment are designed to deal with those that are reasonably soluble ia water. Unfortunately this is a disadvantage for the primary phthalates because they have a very low water solubiUty (ca 50 p.g/L) and this can lead to erroneous test results. The most common problem is seen ia toxicity tests on daphnia where the poorly water-soluble substance forms a thin film on the water surface within which the daphnia become entrapped and die. These deaths are clearly not due to the toxicity of the substance but due to unsuitable test design. 

Iodine. Iodine has been important for many years, primarily as an antiseptic (see Iodine and iodine compounds). In the American Civil War physicians used it to treat battie wounds. Elemental iodine is not very soluble in water, but dissolves readily when sodium iodide is added, forming triiodide + I I Iodine may thus be used as an aqueous solution but it has generally been used as a tincture of 2% iodine in 70% alcohol. Tests on... 

The solubility of water vapor in ionic liquids is of interest because ionic liquids are extremely hygroscopic. In addition, the solubility of water vapor in ILs is an excellent test of the strength of molecular interactions in these fluids. By using the gravi-... 

We have seen in Experiment 8 that silver chloride has low solubility in water. This is also true for silver bromide and silver iodide. In fact, these low solubilities provide a sensitive test for the presence of chloride ions, bromide ions, and iodide ions in aqueous solutions. If silver nitrate... 

Benzoic acid is sparingly soluble in water (which is a disadvantage) and must therefore be dissolved in 95 per cent ethanol. The mode of use is similar to that already described for potassium hydrogenphthalate (Section 10.27, Procedure B). For a 0.1 M solution, of, say, sodium hydroxide, weigh out accurately 0.4 g portions of the acid into a 250 mL conical flask, add 10- 20 mL of ethanol, shake until dissolved, and then titrate the solution with the strong alkali using phenolphthalein as indicator. A blank test should be made with the same volume of ethanol and the indicator deduct, if necessary, the volume of the alkali solution consumed in the blank test. 

The final residue from the mother liquor is an oil which does not solidify in a freezing mixture, and appears to be a mixture of p- and w-tolylcarbinols. Only a trace of phthalic acid (phenolphthalein test) was obtained by oxidizing this oil with permanganate the portion of it which was more readily soluble in water yielded a phenylurethan which depressed the melting point of the phenylurethan of either />-tolylcarbinol or benzyl alcohol. 

The product, calcium hydroxide, is commonly known as slaked lime because, as calcium hydroxide, the thirst of lime for water has been quenched (slaked). Slaked lime is the form in which lime is normally sold because quicklime can set fire to moist wood and paper. In fact, the wooden boats that were once used to transport quicklime sometimes caught fire in the heat of reaction when water seeped into their holds. An aqueous solution of calcium hydroxide, which is slightly soluble in water, is called lime water. It is used as a test for carbon dioxide, with which it reacts to form a suspension of the much less soluble calcium carbonate ... 

Many derivatives of phenol are now made by a synthetic process. Homologous series of substituted derivatives have been prepared and tested for antimicrobial activity. A combination of alkyl substitution and halogenation has produced useful derivatives including clorinated phenols which are constituents of a number of proprietary disinfectants. Two ofthe most widely used derivatives are/ -chloro-m-cresol (4-chloro-3-methylphenol, chlorocresol, Fig. 10.7C) which is mostly employed as a preservative at a concentration of 0.1%, and / -chloro-m-xylenol (4-chloro-3,5-dimethylphenol, chloroxylenol. Fig. 10.7C) which is used for skin disinfection, although less than formerly. Chloroxylenol is sparingly soluble in water and must be solubihzed, for example in a suitable soap solution in conjunction with terpineol or pine oil. Its antimicrobial capacity is weak and is reduced by the presence of organic matter. 

These batch procedures for enrichment and successive transfer may be replaced by the use of continuous culture. This may be particularly attractive when the test compound is toxic, when it is poorly soluble in water, or where the investigations are directed to substrate concentrations so low that clearly visible growth is not to be expected. These problems remain, however, for subsequent isolation of the relevant organisms. One considerable problem in long-term use arises from growth in the tubing of the pump system that is used to administer the medium and should be renewed periodically. 

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