Soluble substances

Rainwater for instance will pick up atmospheric COg and react with calcium carbonate (limestone) to form a soluble substance, calcium bicarbonate. This reaction gives water its natural hardness . 

When polymers or other water-soluble substances are present in the sample, it is advantageous to add a small amount of chloroform to the initial reaction mixture after the subsequent addition of water, a two-phase system results which may be titrated in the usual way to a starch end point or by observing the disappearance of the iodine colour in the chloroform layer. 

Generalizations. Several generalizations can be made regarding taste (16,26). A substance must be in water solution, eg, the Hquid bathing the tongue (sahva), to have taste. Water solubiUty is the first requirement of the taste stimulus (12). The typical stimuli are concentrated aqueous solution in contrast with the Hpid-soluble substances which act as stimuli for olfaction (22). Many taste substances are hydrophilic, nonvolatile molecules (15). Taste detection thresholds for lipophilic molecules tend to be lower than those of their hydrophilic counterparts (16). 

Environmental Effects of Plasticizers. Measurement of the effect of phthalates on environmental species is difficult because standard test methods are not designed to deal with poorly water-soluble substances. Eor this reason a number of early studies are flawed and their results should be disregarded in favor of more recent investigations where these difficulties have been overcome. 

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. 

Sedimentation is also used for other purposes. For example, relative motion of particles and Hquid iacreases the mass-transfer coefficient. This motion is particularly useful ia solvent extraction ia immiscible Hquid—Hquid systems (see Extraction, liquid-liquid). An important commercial use of sedimentation is ia continuous countercurrent washing, where a series of continuous thickeners is used ia a countercurrent mode ia conjunction with reslurrying to remove mother liquor or to wash soluble substances from the soHds. Most appHcations of sedimentation are, however, ia straight sohd—Hquid separation. 

Infusion Method. Infusion is a classic method for top-fermented beers and is used for ad British types. The whole mash is heated graduady from mashing-in to mashing-off with holding times for the degradation of protein and starch. No part of the mash is boiled and the malt, therefore, must be well-modified to assure the breakdown of ad soluble substances. Because no boiling takes place there is no physical breakdown of the malt, and consequentiy infusion is not as effective as decoction despite the better protection of the enzymes. 

A given enzyme may be assayed by its action on soluble substrates under chemical and physical conditions different from those encountered in a real-life wash. Such experiments indicate the enzyme s performance with respect to pH and temperature variations, or in conjunction with other soluble substances, etc. The analytical data thus obtained are not necessarily representative of the wash performance of the enzyme, and real wash trials are necessary to evaluate wash performance of detergent enzymes. 

Liquid-liquid extraction is a process for separating components in solution by their distribution between two immiscible liquid phases. Such a process can also be simply referred to as liquid extraction or solvent extraction however, the latter term may be confusing because it also applies to the leaching of a soluble substance from a solid. 

Persistent and semi-persistent lipophilic (fat soluble) substances known to accumulate in fatty tissue. 

An important purpose of agitation or mixing is to bring a number of materials together in a physically homogeneous mixture. Two or more fluids are either blended or dispersed as emulsions fluids and finely divided solids are dispersed as suspensions, gases dispersed as fluids, or soluble substances dissolved. Mixing of process fluids is reviewed in Chapter 7. 

The range of pore sizes in which TSK-GEL PW and TSK-GEL PWxi columns are available permits a wide spectrum of water-soluble substances to be analyzed. Calibration curves for polyethylene glycols chromatographed on... 

Climatic conditions, age, and the digestion process influence not only the structure of fibers but also the chemical composition. Mean values of components of plant fibers are shown in Table 4. With the exception of cotton, the components of natural fibers are cellulose, hemi-cellu-lose, lignin, pectin, waxes, and water-soluble substances. 

In the case of a sparingly soluble substance, if each of the quantities in (64) is divided by Avogadro s constant, we confirm the statement made above— namely, that, if AS at per ion pair is added to the contribution made to the entropy of the crystal by each ion pair, in this way we evaluate the contribution made by one additional ion pair to the entropy of the saturated solution and it is important to grasp that this contribution depends only on the presence of the additional pair of ions in the solution and does not depend on where they have come from. They might have been introduced into the solution from a vacuum, instead of from the surface of a solid. In (64) the quantities on the right-hand side refer to the solution of a crystal, but the quantity (S2 — Si) does not it denotes merely a change in the entropy of a solution due to the presence of additional ions, which may have come from anywhere. When Si denotes the entropy of a sufficiently large amount of solution, (S2 — Si) is the partial molal entropy of the solute in this solution. 

Before we can decide whether there is a large or a small difference between the unitary terms of the Cl" ions and the 1 ion, the difference in the cratic term must be calculated. The question is whether the difference of 41.0 e.u. between 116.8 and 75.8 merely represents the difference between the cratic terms, or whether it includes as well a difference between the uuitary terms of the I" ion and the Cl" ion. For ions provided by any two such sparingly soluble substances this question can be settled at once by a simple calculation. 

Use Figures 10-5 and 10-6 or Table 10-1 to decide which of the following soluble substances would permit a separation of aqueous magnesium and barium ions. For those that are effective, write the equation for the reaction that occurs. 

It is usual in writing equations involving equilibria between completely dissociated and slightly dissociated or sparingly soluble substances to employ the ions of the former and the molecules of the latter. The reaction is therefore written ... 

Appreciable errors may also be introduced by post-precipitation. This is the precipitation which occurs on the surface of the first precipitate after its formation. It occurs with sparingly soluble substances which form supersaturated solutions they usually have an ion in common with the primary precipitate. Thus in the precipitation of calcium as oxalate in the presence of magnesium, magnesium oxalate separates out gradually upon the calcium oxalate the longer the precipitate is allowed to stand in contact with the solution, the greater is the error due to this cause. A similar effect is observed in the precipitation of copper or mercury(II) sulphide in 0.3M hydrochloric acid in the presence of zinc ions zinc sulphide is slowly post-precipitated. 

If the solution is dilute (which restricts the theory to sparingly soluble substances) we have ... 

The theory of the depression of freezing-point of a solvent by addition of a soluble substance considered in 132 is based on... 

Modern purification methods employ Na sulfite solns to react with the 0 and 7 -TNT isomers to form water soluble substances which can then be washed out of the desired a-TNT-However, these water washes form a blood-red soln — the bothersome red-water of TNT plants. Modern methods of disposing of red-water will be described in Section X... 

Calcium salts have a low solubility in water but this is only true for dodecyl and higher sulfates. Pure octyl and decyl calcium sulfates are soluble substances. 

Determine Ksp for each of the following sparingly soluble substances, given their molar solubilities (a) AgBr, 8.8 X... 

Use the data in Table 11.4 to calculate the molar solubility of each sparingly soluble substance in its respective solution ... 

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