Demonstrations Chemical Change

Dinkelaker B., Hahn G., Romheld V., Wolf G.A, Marschner H. Non-destructive methods for demonstrating chemical changes in the rhizosphere 1. Description of method. Plant Soil 1993 155/156 67-70. 

In this demonstration, chemical changes occur. With the addition of heat, reactants change into products. New substances are formed with new physical properties. Chemistry is the study of chemical change. 

The relationship between current flow and chemical reactions was estabUshed by Faraday who demonstrated that the amount of chemical change was directly proportional to the quantity of charge passed (//) and to the equivalent weight of the reacting material. 

Many cliciiiical reactions evolve or absorb heat. When applying energy balances (consenatioit law for energy) in tccluiical calculations the heat (enthalpy) of reaction is often indicated in mole units so that tliey can be directly applied to demonstrate its chemical change. To simplify the presentation that follows, examine the equation ... 

The correlation of phosphate precipitation with decrease of conductivity (Wilson Kent, 1968), increase in pH (Kent Wilson, 1969) and hardness (Wilson et al, 1972) is shown in Figure 6.16. These results demonstrate the relationship between the development of physical properties and the underlying chemical changes, but there are no sharp changes at the gel point. Evidence from infrared spectroscopy (Wilson Mesley, 1968) and electron probe microanalysis (Kent, Fletcher Wilson, 1970 Wilson et al, 1972) indicates that the main reaction product is an amorphous aluminophosphate. Also formed in the matrix were fluorite (CaF ) and sodium acid phosphates. 

Robinson, Memoirs, 1417, 4750, 66. Weizmann studied chemical change induced by bacteria, which he demonstrated to be a means of manufacturing acetone during the First World War (47). 

The inversion in an Sn2 reaction can be demonstrated in a rather simple experiment. If (- -)-(l )-2-iodobutane is heated in acetone solution, it is recovered unchanged. However, when sodium iodide is added to the mixture, there is no apparent chemical change, but the optical activity gradually diminishes until it becomes zero, i.e. racemic ( )-(i 5 )-2-iodobutane has been formed (see Section 3.4.1). 

It is not sensible to try to cover a wide range of enzymic reactions to demonstrate how amino acid side-chains are responsible for the chemical changes the enzyme brings about. Instead, one or two suitable examples will suffice to illustrate the general principles. 

Results of these investigations demonstrate that changes of the reactor surface can be an effective method for directing chemical reactions. Thus, developing a theory of how heterogeneous factors influence liquid-phase chain reactions is one of the important lines of advancement in this area. Only a few years ago it was thought, almost a priori, that there are practically no heterogeneous factors in liquid-phase oxidation and that liquid-phase processes differ from vapor-phase processes in this respect. 

Selective chemical change of the serine—OH group to cysteine—SH in enzymes can be performed with extremely reactive serine residues in the active sites by the use of phenylmethylsulfonyl fluoride and, subsequently, thioacetic acid (Polgar and Bender, 1966). This selective chemical modification demonstrates the essential role of an—OH... 

Sodium metabisulfite is an antioxidant agent widely used in pharmaceutical preparations to reduce or prevent oxidation. There are some studies, however, that have shown that metabisulfite, under specific conditions, may have indirect oxidant properties. Baker et al. [37] demonstrated that sulfite propofol emulsion, but not EDTA propofol emulsion, underwent chemical changes during a simulated intravenous infusion. Compounds were identified as propofol oxidation products. The increase of propofol oxidation products demonstrated that sulfite from metabisulfite created a strong oxidant environment when air was introduced. Lavoie et al. [38]... 

These data demonstrate that changes in foam properties of liquid cyclone processed cottonseed flour are inducible by treatment with succinic anhydride. Gel electrophoretic and solubility data show that there are alterations in the physical and chemical properties of proteins, and in certain cases these changes improve foam properties, that is, improve solubility and polypeptide dissociation of proteins at the interface of the foaming solution. Similar results have been reported for succinylated soybean and sunflower seed proteins (44. 46). 

The examples show that pressure usually does not promote chemical coalificadon—but undoubtedly it changes the coal physically. As is well known, clays are very sensitive to the action of overburden pressure, under which they lose moisture and porosity. Peats and brown coals have much the same characteristics as clays. This can be readily demonstrated experimentally by compressing brown coals at room temperature. The process does not involve any chemical changes but only a compression and consolidation, attended by an appreciable shrinkage in volume and emission of moisture. Figure 10 shows the action of a pressure of 270 kg./sq. cm. corresponding to an overburden of 1300 meters, upon a xylite from a soft brown coal. The... 

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