Practical work

Teachers of chemistry (and of the sciences generally) will have found that many students appear to dissociate their practical work sharply in their minds from their theoretical knowledge. Many... 

If very many measurements are made of the same variable a , they will not all give the same result indeed, if the measuring device is sufficiently sensitive, the surprising fact emerges that no two measurements are exactly the same. Many measurements of the same variable give a distribution of results Xi clustered about their arithmetic mean p. In practical work, the assumption is almost always made that the distribution is random and that the distribution is Gaussian (see below). 

Practice working with your Learning By Modeling software Construct molecular models of ethane ethylene and acetylene and compare them with respect to their geometry bond angles and C—H and C—C bond distances... 

The existence of tridymite as a distinct phase of pure crystalline siUca has been questioned (42,58—63). According to this view, the only tme crystalline phases of pure siUca at atmospheric pressure are quart2 and a highly ordered three-layer cristobaUte having a transition temperature variously estimated from 806 250°C to about 1050°C (50,60). Tridymites are considered to be defect stmctures in which two-layer sequences predominate. The stabihty of tridymite as found in natural samples and in fired siUca bricks has been attributed to the presence of foreign ions. This view is, however, disputed by those who cite evidence of the formation of tridymite from very pure siUcon and water and of the conversion of tridymite M, but not tridymite S, to cristobahte below 1470°C (47). It has been suggested that the phase relations of siUca are deterrnined by the purity of the system (42), and that tridymite is not a tme form of pure siUca but rather a soHd solution of minerali2er and siUca (63). However, the assumption of the existence of tridymite phases is well estabUshed in the technical Hterature pertinent to practical work. 

Instead of calculations, practical work can be done with scale models (33). In any case, calculations should be checked wherever possible by experimental methods. Using a Monte Carlo method, for example, on a shape that was not measured experimentaUy, the sample size in the computation was aUowed to degrade in such a way that the results of the computation were inaccurate (see Fig. 8) (30,31). Reversing the computation or augmenting the sample size as the calculation proceeds can reveal or eliminate this source of error. 

This example is a simplified one. The cost of the working capital is assumed to be paid for in Y ear 0 and returned in Y ear 10. In practice, working capitalincreases with the production rate. Thus there may be an annual expenditure on working capital in a number of vears subsequent to Y ear 0. Except in loss-making years, this is usually treated as an expense of the process. In loss-making years the cash injection for working capital is included in the At for that year. 

The practical working equation for weight rate of discharge, adoptea by the ASME Research Committee on Fluid Meters for use with either gases or liquids, is... 

The enforcement of codes of practice, working procedures and general instructions incorporating all possible safety factors. 

There is no need to emphasize that many helpful hands are required in the compilation of such a review. Our particular thanks are due to Mrs. E. Kany, Mrs. I. Klein and Mrs. S. Netz together with Dipl.-Ing. M. Heiligenthal for their conscientious execution of the practical work. 

In conclusion I desire to thank Dr. J. McCrae, who has written the section on Ethyl Tartrate and the use of the Polari-meter. Dr. T. S. Patterson, who has been kind enough to look over the proofs, and Mr. H. D. Dakin, who has given me substantial assistance in the practical work of revision. 

This section is concerned with describing the equipment which is necessary for an introduction to spectrographic techniques for the analyst. In this instance the practical work will be described for instruments manufactured by Rank Hilger, Margate, Kent, UK, but the comparable products of other manufacturers may also be used. 

While virial coefficients can be calculated from statistical-mechanical formulas, for practical work it is usually more convenient to employ semi-empirical correlations. Most of these correlations are based on the principle of corresponding states and as a result their applicability is limited to normal... 

Hodson, D. (1990). A critical look at practical work in school science. School Science Review, 71(256), 33 0. 

This section discusses the value of laboratory practical work in providing a sound basis for the development of an understanding of the triplet relationship. Whilst the first three chapters deal with the macro experience and show how progression to the submicro and symbolic can be faciUtated, the last starts from the opposite extreme and shows the value of working from the basis of diagrams. 

Learning at the Macro Level The Role of Practical Work... 

Chemistry is basically an experimental science, hence the contact, especially through the laboratory and practical work, with concrete examples of substances, their reactions and other properties, is an essential and integral part of chemical education. The laboratory is therefore the proper place for keeping chemistry tangible. 

The terms laboratory work and practical work are used in the literatrrre without precise defirrition to embrace mtmerous activities in science irrstructioa According to Hodson (1990), the term practical work means tasks in which students observe or manipirlate real objects or materials for themselves (individually or in small groups) or by witnessing teacher demonstratiorrs. In an extended sense, practical work involves not orrly work in the formal chemistry laboratory or demonstratiorrs, but also ar r type of activity that involves tangible objects, and provides students the opportrrrrity to manipirlate and interact with chemicals and observe chemistry in action corrsequently, home laboratory kits and computer simulations of experiments are also included. 

Educationists usually place the emphasis on the cognitive objectives of practical work. Of equal importance are however factors of the affective domain. Gott Mashiter (1991, p. 61) proposed that practical tasks should have within them the elements of motivation that stem from confidence in and a sense of ownership of the activity by the stndent . Motivation, however, requires not only a measnre of self-directedness by the learner but also interesting and exciting experiments (Hodson, 1996). 

As a result of science education research, a new era of reform in science education has started with the new centuiy. New standards have been fixed (National Research Council, 1996, 2000). The National Science Education Standards (National Research Council, 1996) and also the 2061 project of ihe American Association for the Advancement of Science (1989,1990) assume that inquiry in general and inquiry in the context of practical work in science education is central to the achievement of scientific literacy (Hofstein Mamlok-Naaman, 2007). 

Bennett, S. W., O Neale, K. (1998). Skills development and practical work in chemistry. University Chemistry Education, 2, 58-62. 

Brattan, D, Mason, D., Best, A. J. (1999). Changing the nature of physical chemistry practical work. University Chemistry Education, 3, 59-63. 

Buckley, J. G., Kempa, R. F. (1971). Practical work in sixth-form chemistry courses An enquiry. 

Gott, R., Mashiter, J. (1991). Practical work in science A task-based approach In B. Woolnough (Ed.), Practical science (pp. 53-66). Buckingham, UK Open University Press. 

Hirvonnen P. E., Virii, J. (2002). Physics student teachers ideas about the objectives of practical work. Science Education, 11, 305-316. 

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