Preparing for the Laboratory

A common misconception students have about performing experiments is that it is much like cooking that is, you merely follow the directions given— the recipe — and the desired product or data will result. Such students enter the laboratory expecting to follow the experimental procedure in a more or less rote manner. This unfortunate attitude can lead to inefficiencies, accidents, and minimal educational benefit and enjoyment from the laboratory experience. 

To be sure, cooking is somewhat analogous to performing experiments. The successful scientist, just like a five-star chef, is a careful planner, a diligent worker, a keen observer, and is fully prepared for failures Experiments may not work despite your best efforts, just as a cake may fall even in the hands of a premier pastry chef. 

The specific details of what you should do before coming to the laboratory will be provided by your instructor. However, to help you prepare in advance, we have developed a set of Pre-Lab Exercises for each of the experimental procedures we describe. These exercises are Web-based and are foimd at the URL given in the margin you should bookmark this URL, as you will be visiting it frequently while preparing for each experimental procedure. In addition, the icon shown in the margin will appear whenever Web-based material is available. 

Your instructor may require you to submit answers to the Pre-Lab Exercises for approval before authorizing you to proceed with the assigned experiments. Even if you are not required to submit the exercises, though, you will find that working them prior to the laboratory period will be a valuable educational tool to self-assess your understanding of the experiments to be performed. 

You undoubtedly will be required to maintain a laboratory notebook, which will serve as a complete, accurate, and neat record of the experimental work that you do. Once more, your instructor will provide an outline of what specific information should appear in this notebook, but part of what is prescribed will probably necessitate advance preparation, which will further enhance your ability to complete the experiments successfully. The laboratory notebook is a permanent record of your accomplishments in the course, and you should take pride in the quality and completeness of its contents  

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A9.2.4. Laboratory Selector. No drawings have been prepared for the laboratory selector unit as its construction will be very similar to the shuttle transfer unit. It differs only in the arrangement and number of tubes required for servicing the laboratories. The selector can be located close to the transfer unit or it can be set up at some convenient location in- the laboratory building. 

Iodine is rarely prepared in the laboratory the method used is the oxidation of an iodide by manganese(IV) oxide and sulphuric acid, for example with sodium iodide ... 

It should be noted that a number of different enzyme preparations can now be purchased directly from manufacturing chemists. It must be emphasised that the activity of an enzyme, whether purchased or prepared in the laboratory, may vary between rather wide limits. The activity is dependent on the source of the enzyme, the presence of poisons and also on the temperature. It appears, for example, that the quality of horseradish peroxidase depends upon the season of the year at which the root is obtained from the ground. It cannot be expected therefore that all the experiments described below will work always with the precision characteristic of an organic reaction proceeding under accurately known conditions. 

Secondary and tertiary amines are not generally prepared in the laboratory. On the technical scale methylaniline is prepared by heating a mixture of aniline hydrochloride (55 parts) and methyl alcohol (16 parts) at 120° in an autoclave. For dimethylaniline, aniline and methyl alcohol are mixed in the proportion of 80 78, 8 parts of concentrated sulphuric acid are added and the mixture heated in an autoclave at 230-235° and a pressure of 25-30 atmospheres. Ethyl- and diethyl-anihne are prepared similarly. One method of isolating pure methyl- or ethyl-aniline from the commercial product consists in converting it into the Y-nitroso derivative with nitrous acid, followed by reduction of the nitroso compound with tin and hydrochloric acid ... 

Benzoquinone ( quinone ) is obtained as the end product of the oxidation of aniline by acid dichromate solution. Industrially, the crude product is reduced with sulphur dioxide to hydroquinone, and the latter is oxidised either with dichromate mixture or in very dilute sulphuric acid solution with sodium chlorate in the presence of a little vanadium pentoxide as catalyst. For the preparation in the laboratory, it is best to oxidise the inexpensive hydroquinone with chromic acid or with sodium chlorate in the presence of vanadium pent-oxide. Naphthalene may be converted into 1 4-naphthoquinone by oxidation with chromic acid. 

These thermal methods for preparing amides are limited m their generality Most often amides are prepared m the laboratory from acyl chlorides acid anhydrides or esters and these are the methods that you should apply to solving synthetic problems... 

Among compounds other than simple alkyl halides a halo ketones and a halo esters have been employed as substrates m the Gabriel synthesis Alkyl p toluenesul fonate esters have also been used Because phthalimide can undergo only a single alkyl ation the formation of secondary and tertiary amines does not occur and the Gabriel synthesis is a valuable procedure for the laboratory preparation of primary amines... 

Preparation. In the laboratory, sulfur tetrafluoride is made by combining SCI2 and NaF suspended in acetonitrile at ca 77°C (106). For commercial production, SF is made by direct combination of sulfur with elemental fluorine (107). Commercial appHcations of SF are limited. It is available from Air Products and Chemicals. 

Microscopic sheets of amorphous silica have been prepared in the laboratory by either (/) hydrolysis of gaseous SiCl or SiF to form monosilicic acid [10193-36-9] (orthosihcic acid), Si(OH)4, with simultaneous polymerisation in water of the monosilicic acid that is formed (7) (2) freesing of colloidal silica or polysilicic acid (8—10) (J) hydrolysis of HSiCl in ether, followed by solvent evaporation (11) or (4) coagulation of silica in the presence of cationic surfactants (12). Amorphous silica fibers are prepared by drying thin films of sols or oxidising silicon monoxide (13). Hydrated amorphous silica differs in solubility from anhydrous or surface-hydrated amorphous sdica forms (1) in that the former is generally stable up to 60°C, and water is not lost by evaporation at room temperature. Hydrated sdica gel can be prepared by reaction of hydrated sodium siUcate crystals and anhydrous acid, followed by polymerisation of the monosilicic acid that is formed into a dense state (14). This process can result in a water content of approximately one molecule of H2O for each sdanol group present. 

The performance of a catalyst often depends as much on the care and method of preparation as on the identity of the active components. This fact has been learned by many who have failed to obtain reproducibiUty among catalyst preparations ia the laboratory or have been responsible for quaUty assurance ia catalyst manufacture. Also, there are many examples of strong effects of trace impurities ia raw material or catalyst support on catalyst performance. 

J. M. HoUand and co-workers. Chronic Dermal Toxicity ofEpoyj Resins I. Skin Carcinogenic Potenj and General Toxicity, report ORNL-5762, prepared for the U.S. DOE by Oak Ridge National Laboratory, Oak Ridge, Term., 1981. 

The purpose of this section is to provide guidehnes for this preparation. General aspects are covered. Preparations for the specific units can be drawn from these. Topics include analyst, model, plant, and laboratory preparation. Since no individual analyst can be responsible for all of these activities, communication with other personnel is paramount for the success of the analysis. 

The laboratory may need time to prepare for the unit test. This must be accounted for when the test is scheduled. The analysis of... 

There are three general methods of interest for the preparation of vinyl chloride, one for laboratory synthesis and the other two for commercial production. Vinyl chloride (a gas boiling at -14°C) is most conveniently prepared in the laboratory by the addition of ethylene dichloride (1,2-dichloroethane) in drops on to a warm 10% solution of sodium hydroxide or potassium hydroxide in a 1 1 ethyl alcohol-water mixture Figure 12.1). At one time this method was of commercial interest. It does, however, suffer from the disadvantage that half the chlorine of the ethylene dichloride is consumed in the manufacture of common salt. 

Dehydrogenation of alkanes is not a practical laboratory synthesis for the vast majority of alkenes. The principal methods by which alkenes are prepared in the laboratory are two other p eliminations the dehydration of alcohols and the dehydrohalo-genation of alkyl halides. A discussion of these two methods makes up the remainder of this chapter. 

Figure 26.7. Isoborneol, a stereoisomer of borneol, can be prepared in the laboratory by a two-step sequence. In the first step, borneol is oxidized to camphor by treatment with chromic acid. In the second step, camphor is reduced with sodium borohydride to a mixture of 85% isoborneol and 15% borneol. On the basis of yj hese transformations, deduce structural formulas for isoborneol and camphor, j...

Most laboratories report results for the INR along with the patient s PT and the control value. The INR was devised as a way to standardize PT values and represents a way to correct the routine PT results from different laboratories using various sources of thromboplastin and methods of preparation for the test. The INR is determined by a mathematical equation comparing the patient s PT with the standardized PT value. Some institutions may use only PT, others PT/INR, and some may use INR. The INR is maintained between 2 and 3. 

Used either as prelaboratory preparation for related laboratory activities or to expose students to additional laboratory activities not available in their program, these modules motivate students to learn by proposing real-life problems in a virtual environment. Students make decisions on experimental design, observe reactions, record data, interpret these data, perform calculations, and draw conclusions from their results. Following a summary of the module, students test their understanding by applying what they have learned to new situations or by analyzing the effect of experimental errors. 

A note on good practice Whether or not a reaction is spontaneous depends on the composition, so it is better to say that K > 1 for a reaction rather than that it is spontaneous. However, for reactions with very large equilibrium constants, it is very unlikely that the mixture of reagents prepared in the laboratory will correspond to 2 > K, and it is common to refer to such reactions as spontaneous. ... 

Fluorine comes from the minerals fluorspar, CaF, cryolite, Na3AlF6 and the fluorapatites, Ca,F(P04)3. The free element is prepared from HF and KF by electrolysis, but the HF and KF needed for the electrolysis are prepared in the laboratory. Chlorine primarily comes from the mineral rock salt, NaCl. The pure element is obtained by electrolysis of liquid NaCl. Bromine is found in seawater and brine wells as the Br ion it ts also found as a component of saline deposits the pure element is obtained by oxidation of Br (aq) by Cl,(g). Iodine is found in seawater, seaweed, and brine wells as the I" ion the pure element is obtained by oxidation of I (aq) by Cl,(g). 

The two examples of sample preparation for the analysis of trace material in liquid matrixes are typical of those met in the analytical laboratory. They are dealt with in two quite different ways one uses the now well established cartridge extraction technique which is the most common the other uses a unique type of stationary phase which separates simultaneously on two different principles. Firstly, due to its design it can exclude large molecules from the interacting surface secondly, small molecules that can penetrate to the retentive surface can be separated by dispersive interactions. The two examples given will be the determination of trimethoprim in blood serum and the determination of herbicides in pond water. 

A quite surprising development, even to experienced workers in elemental-fluorine chemistry, has been the synthesis of trifluoromethyl organometallic compounds by direct fluorination of metal alkyls (25). Even more surprising is the fact that, for certain metal and metalloid systems, such as the reaction of elemental fluorine with tetramethyl-germane, this t5rpe of low-temperature synthesis is a practical method 26) for the laboratory preparation of the perfluoro analog. 

For these reasons, despite the apparent advantages and also despite the fact that bulk polymerisation is so often the method of choice for the laboratory preparation of vinyl polymers, this technique is not widely used in industry. Only three polymers are produced in this way, namely poly(ethylene), poly(styrene), and poly(methyl methacrylate). 

Students had the opportunity to cany out most of the chemical reactions referred to above in preparation for the quahtative analysis component of the practical examination that involved the identification of several ions and gases. The only other practical experience involving chemical reactions that students would have encountered was when they prepared samples of soluble and insoluble salts in the laboratory using one or more methods previously discussed in class. 

DTI (2002) Tributyitin in consumer products. Report prepared by the Laboratory of the Government Chemist for the United Kingdom Department of Trade and Industry, by letter dated 8 March 2002. 

At the time of its discovery in 1970, few chemical methods were known for the laboratory syntheses of such molecules. Fewer still were appropriate for their industrial scale production. Unlike many other amino acid derivatives, gl rphosate is stable in strong acid or base, even at elevated temperatures. It can also tolerate strong reductants and some oxidants (1,2). This stability accounts for the diversity of synthetic methods that have been explored and developed to prepare glyphosate and its heterocyclic derivatives over the last 25+ years. 

Several environment-friendly surface preparation for the treatment of mbber soles with radiations have been recently studied. These treatments are clean (no chemicals or reactions by-products are produced) and fast, and furthermore online bonding at shoe factory can be produced, so the future trend in surface modification of substrates in shoe industry will be likely directed to the industrial application of those treatments. Corona discharge, low-pressure RF gas plasma, and ultraviolet (UV) treatments have been successfully used at laboratory scale to improve the adhesion of several sole materials in shoe industry. Recently, surface modification of SBR and TR by UV radiation has been industrially demonstrated in shoe industry... 

XPS spectra were obtained for the catalysts in the calcined, sulfided, and sometimes in the reduced state, as described before. Table III gives the binding energies and relative surface concentrations for the M0/AI2O3 and C0-M0/AI2O3 catalysts, with and without arsenic. Data for the used catalysts, which are not listed in the table, are similar to those for the catalysts prepared in the laboratory. 

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