Scale forming compounds

Properties Miscible with water but insoluble in organic solvents. It possesses sequestering, dispersing, and deflocculating properties and precipitates proteins. In very low concentration, it inhibits corrosion of steel and prevents the precipitation of slightly soluble, scale-forming compounds such as calcium carbonate and calcium sulfate. 

Salutsky, M. L., Dunseth, M. G., Eason, W. E., Removal of Scale-Forming Compounds from Sea Water, W. R. Grace Co. Summary Rept. 6 to Office of Saline Water for year ending June 1, 1961, Contract No. 14-01-001-202 Ibid., Report 10, June 1, 1962. 

C) is much more soluble than calcium carbonate (Ksp = 8.7 X at 25°C). Limiting salts can be identified from their values. The deposition of the scale-forming compounds can be limited to an extent by reducing the pH with acid and/or by the use of anti-scaHng chemicals, which interrupt crystal growth at the nucleation stage. 

Summary of Common Inorganic Scale Forming Compounds "... 

While the ambient-temperature operation of membrane processes reduces scaling, membranes are much more susceptible not only to minute amounts of scaling or even dirt, but also to the presence of certain salts and other compounds that reduce their ability to separate salt from water. To reduce corrosion, scaling, and other problems, the water to be desalted is pretreated. The pretreatment consists of filtration, and may include removal of air (deaeration), removal of CO2 (decarbonation), and selective removal of scale-forming salts (softening). It also includes the addition of chemicals that allow operation without scale deposition, or which retard scale deposition or cause the precipitation of scale which does not adhere to soHd surfaces, and that prevent foam formation during the desalination process. 

LSI (Langelier Saturation Index) an indication of the corrosive (negative) or scale-forming (positive) tendencies of the water. Hardness the total dissolved calcium and magnesium salts in water. Compounds of these two elements are responsible for most scale deposits. Units are mg/l as CaCOs. 

Hydrogen is unusual because it can form both a cation (1I+) and ail anion (11 ). Moreover, its intermediate electronegativity (2.2 on the Pauling scale) means that it can also form covalent bonds with all the nonmetals and metalloids. Because hydrogen forms compounds with so many elements (Table 14.2 also see Section 14.2), we shall meet more of its compounds when we study the other elements. 

Nature has provided a wide variety of chiral materials, some in great abundance. The functionality ranges from amino acids to carbohydrates to terpenes (Chapters 2-5). All of these classes of compounds are discussed in this book. Despite the breadth of functionality available from natural sources, very few compounds are available in optically pure form on large scale. Thus, incorporation of a chiral pool material into a synthesis can result in a multistep sequence. However, with the advent of synthetic methods that can be used at scale, new compounds are being added to the chiral pool, although they are only available in bulk by synthesis. When a chiral pool material is available at large scale, it is usually inexpensive. An example is provided by L-aspartic acid, where the chiral material can be cheaper than the racemate. 

Scale is a rock-hard crust that can form in pipes and pots that are used with hard water. Before the general availability of household water softeners, scale was a much more common experience. Insoluble scale forms from calcium ions when carbonate ion is present. This fact highlights, once more, the versatility of carbonates. We have seen carbon dioxide form carbonates and hence carbonic acid in water we have used sodium bicarbonate (baking soda) as a base and finally we have pointed out that carbonates can make fairly insoluble solids. These many talents of the carbonate ion make baking soda good for more than cooking. Baking soda makes an excellent deodorizer because it can react with both acidic and basic smelly compounds and can form nonvolatile, and hence non-smelly, compounds with many more. A lot of chemistry in a little box ... 

Figure 11.2 Energy diagram comparingfluorescenceandphosphorescence.Theshoitaxiowscoue-spond to mechanisms of internal conversion without emission ofphotons. The fluorescence results from transfers between states of the same multiplicity (same spin state) while the phosphorescence results from transfers between states of different multiplicity. The state Tj produces a delay in the return to the fundamental state, which can last several hours. The Stokes shift corresponds to the energy dissipated in the form of heat (vibrational relaxation) during the lifetime of the excited state, prior to photon emission. The real situation is more complex than this simplified Jablonski diagram suggests. To our scale, a compound can be both fluorescent and phosphorescent for, at the molecular scale individual species do not all exhibit the same behaviour.

Molecular theory asserts that all matter is composed of molecules, with molecules made up of one or more atoms. What evidence do we have for the existence of molecules That is, why do we believe that matter is ultimately composed of lumps, rather than being continuous on all scales (For a review of the nineteenth-century debate on the discrete vs. continuous universe, see Nye [4].) One piece of evidence is the law of definite proportions the elements of the periodic table combine in discrete amounts to form compounds. Another piece of evidence is obtained by shining X rays on a crystalline solid the resulting diffraction pattern is an array of discrete points, not a continuous spectrum. More evidence is provided by Brownian motion see Figure 1.2. 

Radon, Rn At. no. 86, at. wt 222, mp—71°C, bp -61.8°C. Radon is an intermediate radioactive decay product of Ra. Rn, the most stable isotope of radon, is obtained as a gas from aqueous solutions of RaCl2 and has been used as a radiation source and as a gaseous tracer. It is a considerable hazard in uranium mines. In some areas, radon in basements and in ground water is a potential health hazard because of its radioactivity. The ground state electronic configuration of radon is [Xe]4f " 5d °6s 6p. Because radon is intensely radioactive, the chemistry of radon has only been investigated on the tracer scale. Radon forms compounds, particularly a fluoride (likely RnF2), and solid adducts between the fluoride and Lewis acid fluorides. 

In your study of chemistry so far, you ve learned how to name compounds, balance equations, and calculate reaction yields. You ve seen how heat is related to chemical and physical change, how electron configuration influences atomic properties, how elements bond to form compounds, and how the arrangement of bonding and lone pairs accounts for molecular shapes. You ve learned modem theories of bonding and, most recently, seen how atomic-scale properties give rise to the macroscopic properties of gases, liquids, solids, and solutions. 

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