Media Mistakes

These considerations illustrate why it is easy to mistake lack of agreement between calculated and experimental values of kn, due to the assumption of an incorrect reaction mechanism, for a medium effect. If the model of a reaction to which the simple equilibrium theory is applied is in error, the solvent isotope effect expression (56) will contain some incorrect factors of the form (1 — n + mf)). Suppose, for example, that the expression (48) or (49)—applicable to a reaction of A-l mechanism—is used in conjunction with experimental data for an A-2 mechanism. Analysis of the results should lead to the conclusion that a factor of the form (1—n + mf>)2 (cf. equation (50)) has been omitted from the required theoretical equation. However, alternatively the conclusion might be drawn that equation (100) ought to have been used in place of (48), and the lack of agreement would then be ascribed to the presence of the factor Y. But Fg is itself a quotient of transfer... 

Chemat et al. [14] found the ]oint use of US and microwaves for the treatment of edible oils for the determination of copper to shorten the time taken by this step to about a half that was required in the classical procedure (heating in a Buchi digester) or with microwave assistance, nitric acid and hydrogen peroxide. However, they did not state the specific medium where the microwave-US-assisted method was implemented and assumed US to have mechanical effects only, even though they mentioned a cavitational effect. This is a very common mistake in working with US that is clarified in an extensive discussion by Chanon and Luche [15] of the division of sonochemistry applications into reactions which were the result of true and false effects. Essentially, these terms refer to real chemical effects induced by cavitation and those effects that can be ascribed to the mechanical impact of bubble collapse. The presence of one of these phenomena only has not been demonstrated in the work of Chemat et al. [14] — despite the illustrative figure in their article — so their ascribing the results to purely mechanical effects of US was unwarranted. 

Place approximately 1 g (by estimation) of each of the dried, sieved soils in separate wells of a porcelain spot plate. Add a small amount of distilled water and stir to remove entrapped air. Then add several drops of 1 M HC1 to each and look for any effervescence. Record the effervescence as none, trace, weak, medium, or strong. Do not mistake entrapped air bubbles for a positive test. 

In Fig. 9b, PC3 seems to have a larger contribution on the system because of the present bands between 1,610 and 1,630 cm . This behavior can be explained because of the variance of the sampling, by the fact that oxidation medium is not totally homogeneous and by the accumulated mistakes from the retreat of the aliquots to making pellets for reading in FTIR [23]. 

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