Writing experimental procedures

The main purpose of the methods described in the experimental section of a laboratory report, project report, thesis or paper is to communicate sufficient information to allow an experienced chemist to repeat, your experiments. One of the goals.Of writing laboratory reports is to provide you with practice in writing in the generally accepted, style required for more professional publications. The following fwiints should be noted  

The following examples illustrate the differences be tween the instructions of the experiment protocol and the. accepted style required for the experimental section. .  

Example 1 A preparative experiment the synthesis of methyl 2,4-dimethylbenzoate 

Note 1. Experimental gives reagents, solvents, quantities, times, yields, etc., and sufficient detail for the experiment to be repeated by a proficient chemist. Details of standard techniques such as weighing liquids, setting up apparatus, recrystallization, drying the product, etc., are understood by the experimentalist from experience and training. 

Note 2. The weights and volumes, usied arc quoted to one decimal place, since this is the level of accuracy required for preparative. experiments which results from the techniques used, distillation, recrystallization, extraction, etc., and the noh-quantitative conversion of the reactants to products may be more significant than errors in weighing. 

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In scientific writing, passive voice is often used to describe experimental procedures (see chapter 3). It is also used to shift the emphasis from the researcher to the research (i.e., from the scientist to the science). The hints provided here will help you avoid some common mistakes made by novice writers when using passive voice. 

I also thank my wife, Christel, who patiently tolerated the lifestyle changes associated with writing a book. In addition, she designed experimental procedures and searched for ideal laboratory conditions for several experiments. I am happy to report that Mausi, our blue-point Himalayan, is still napping under the desk lamp. 

The write-up to this point is to be completed as a Prelab assignment. The experimental procedure followed is then recorded in your notebook as you proceed through the experiment. The detail should be sufficient so that a fellow student can use your notebook as a guide. You should include observations, such as color changes or gas evolution, made during the experiment. If you obtain a recorder printout of numbers, a spectrum from a spectrophotometer, or a photograph, these records must be saved and handed in with your report. 

Although there is no fixed set of writing rules to be followed like a cookbook recipe or an experimental procedure, some guidelines can be helpful. Start by considering the questions in Box 3-1 answering these questions will clarify your goals and make it easier to write the manuscript with the proper amount of detail. It will also make it easier for the book or journal editor to determine the... 

For some routine or exploratory work, it is expedient to adopt a simplified experimental procedure, which involves the determination of a single point on the isotherm -preferably within the BET range. The assumption is then made that C is sufficiently large to give an almost zero intercept. If we assume that the intercept is zero, and that C-1 C we may write ... 

In writing these expressions, it is implicitly assumed that the observations ctij are subject to random errors and that the reaction times (/y—t,o) are free from random errors. The assumption that the random errors occur solely in a is reasonable since, in the majority of kinetic studies, time can be measured with much greater precision than concentration. When the random errors in the determination of time are commensurate with the random errors in the determination of concentration, the above equations are no longer valid we shall not discuss this situation in view of the difficulties which arise but would suggest that, if possible, every effort should be made to avoid it by redesigning the experimental procedure. 

Although there is no fixed set of writing rules to be followed like a cookbook recipe or an experimental procedure, some guidelines can be helpful. Start by answering some questions ... 

F. Denmark, a scientific leader in the relevant area of chemistry who had not been able to reproduce the experimental results. In his retraction Buono writes, At this stage, I asked my co-workers to check the experimental procedures and analytical conditions and to try to reproduce the described results. I was provided with experimental data and material that fully confirmed our original claims. After repetition of the experiments and upon close examination of his students work, however, Buono saw evidence of error. He writes that he noticed several inconsistencies with the analytical material the students had previously provided. Therefore, I decided to reproduce personally and independently the whole experimental procedures from the very beginning. Buono could not reproduce the results originally reported by him and his coworkers, but obtained the results reported by Denmark and his coworkers. Buono concluded this episode by writing that he wished to withdraw [the original] communication. Other pieces of work based on related experimental results that were published elsewhere will also be withdrawn. ... 

Internet World Wide Web Literature Research project. Choose one of the HPLC compound class applications in Section 13.1.7, and use the links in Appendix 13.1 to download manufacturer s application notes, sample chromatograms, and suggested products for their analysis. Write a detailed experimental procedure to separate your chosen compounds. 

An alternative experimental procedure to creep and stress relaxation is to subject the specimen to an alternating strain and simrdtaneously measure the stress. For linear viscoelastic behaviour, when equilibrium is reached, the stress and strain will both vary sinusoidally, but the strain lags behind the stress. Thus we write... 

In an experimental treatment, a person is given boron-10, which is taken up by malignant tumors. When bombarded with neutrons, boron-10 decays by emitting alpha particles that destroy the surrounding tumor cells. Write the balanced equation for the nuclear reaction for this experimental procedure. 

You should now be getting familiar with reading and understanding experimental procedures. Try and write an experimental and work-up procedure for the preparation of pentane-1,5-dioic acid from pentane-1,5-dinitrile. 

Be familiar with common laboratory glassware and apparatus. Be able to write an experimental report in an appropriate style, and be able to follow a written experimental procedure. (Questions 2.1 to 2.4)... 

Procedure. Write a program for solving simultaneous equations by the Gaussian elimination method and enter the absorptivity matiix above to solve Eqs. (2-51). Set up and solve the problem resulting from a new set of experimental observations on a new unknown solution leading to the nonhomogeneous veetor b = 0.327,0.810,0.673. ... 

The standard procedure is to measure D at several different initial concentrations, using the procedure just described, and then extrapolating the results to c = 0. We symbolize the resulting limiting value D°. This value can be interpreted in terms of Eq. (9.79), which is derived by assuming 7 -> 1 and therefore requires extreme dilution. It is apparent from Eqs. (9.79) and (9.5) that D° depends on the ratio T/770, as well as on the properties of the solute itself. In order to reduce experimental (subscript ex) values of D° to some standard condition (subscript s), it is conventional to write... 

Table 1.4 in this section sets forth the procedure to be followed in writing Lewis structures for organic molecules. It begins with experimentally deter-mined infor-mation the molecular formula and the constitution (order in which the atoms are connected). 

The procedure, in analyzing kinetic data by numerical integration, is to postulate a reasonable kinetic scheme, write the differential rate equations, assume estimates for the rate constants, and then to carry out the integration for comparison of the calculated concentration-time curves with the experimental results. The parameters (rate constants) are adjusted to achieve an acceptable fit to the data. Carpen-(ej-48. pp. 76-81 some numerical calculations. Farrow and Edelson and Porter... 

Equally precise and meticulous as an experimentalist, he devoted time during his days at Pittsburgh to write comprehensive articles on such practical techniques as crystallization, vacuum distillation, and sublimation, which were published in the Weissberger Techniques of Organic Chemistry series. His preoccupation with careful experimental techniques and then-accurate recording in the literature remained with him always. He abhorred vague descriptions of procedures, speculative interpretations not based on... 

For your chosen option, write out a complete procedure based on the table on the previous page. Include a diagram showing the experimental set-up, and detailed safety precautions. Have your teacher approve your procedure, and then carry it out. 

The first step in the solution procedure is discretization in the radial dimension, which involves writing the three-dimensional differential equations as an enlarged set of two-dimensional equations at the radial collocation points with the assumed profile identically satisfying the radial boundary conditions. An examination of experimental measurements (Valstar et al., 1975) and typical radial profiles in packed beds (Finlayson, 1971) indicates that radial temperature profiles can be represented adequately by a quadratic function of radial position. The quadratic representation is preferable to one of higher order since only one interior collocation point is then necessary,6 thus not increasing the dimensionality of the system. The assumed radial temperature profile for either the gas or solid is of the form... 

My aim in writing this book has been to give students a solid understanding of the theoretical basis of spectroscopic methods and an appreciation of how these methods provide information on molecular structure. Brief descriptions of experimental spectroscopic procedures are also included. 

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