Acid deposition characteristics

Using Environmental Examples to Teach About Acids. Acid-base reactions are usually presented to secondary students as examples of aqueous equilibrium (2). In their study of acids and bases, students are expected to master the characteristic properties and reactions. They are taught to test the acidity of solutions, identify familiar acids and label them as strong or weak. The ionic dissociation of water, the pH scale and some common reactions of acids are also included in high school chemistry. All of these topics may be illustrated with examples related to acid deposition (5). A lesson plan is presented in Table I. 

Impubities.—rhosphorus is rarely adulterated, and the only impurities contained in it are those derived from the acid used in its preparation. Dumas considers flexibility as a characteristic of good phosphorus. Occasionally arsenic, antimony, bismuth, and some other metals have boon found in it. If the acid used contained arsenioua acid, or an oxide of antimony, these are reduced in the process of manufacture of phosphorus, and are found in it in the metallic state. A solution of phosphorus in dilute nitrio acid should give no precipitate with sulphide of hydrogen, and the precipitate procured by a barytic salt should be entirely soluble in excess of nitric acid, proving the absence of sulphur. If arsenic is present, the solution in nitrio acid deposits a black precipitate of metallic arsenic when submitted to evaporation. 

In Norway and Sweden, to what extent are these characteristics being adversely affected by the acid deposition itself ... 

To establish the effects on human health of the fallout of the chemical species formed in the atmosphere, we have to distinguish between acid depositions and substances like ozone, PAN or other peroxides. In this case we have to follow a different approach, that is, we must establish, as proposed by WHO, the limits for some characteristic contaminants. 

Once the inputs euid orrtputs are determined, the second and third steps of LCA, impact analysis and improvement analysis, can be prrrsued (Fava et al. 1991). For impact analysis, the analyst Unks the inventory of a substance released to an envirorrmental load factor such as acid deposition, which is defined in Table 6 (Potting et al. 1998). Environmental load factors are a frmetion of characteristics such as location, merlirrm, time, rate of release, route of exposrrre, natural environmental process mechanisms, persistence, mobility, accrrmrrlation, toxicity, and threshold of effect. Owens argues that because inventory factors do not have the spatial, temporal, or threshold characteristics that are inherent to the environmental load, other risk-assessment tools shorrld be used to evaluate a local process (Owens 1997). 

Chemical Analysis. The presence of siUcones in a sample can be ascertained quaUtatively by burning a small amount of the sample on the tip of a spatula. SiUcones bum with a characteristic sparkly flame and emit a white sooty smoke on combustion. A white ashen residue is often deposited as well. If this residue dissolves and becomes volatile when heated with hydrofluoric acid, it is most likely a siUceous residue (437). Quantitative measurement of total sihcon in a sample is often accompHshed indirectly, by converting the species to siUca or siUcate, followed by deterrnination of the heteropoly blue sihcomolybdate, which absorbs at 800 nm, using atomic spectroscopy or uv spectroscopy (438—443). Pyrolysis gc followed by mass spectroscopic detection of the pyrolysate is a particularly sensitive tool for identifying siUcones (442,443). This technique rehes on the pyrolytic conversion of siUcones to cycHcs, predominantly to [541-05-9] which is readily detected and quantified (eq. 37). 

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