Preparation for an Experiment

Before you arrive in the laboratory to perform a given experiment, it is essential that you study the experiment carefully, with special emphasis on the method, the apparatus design, and the procedure. It will usually be necessary to make changes in the procedtrre whenever the apparatus to be used or the system to be studied differs from that described in this book. Plaiming such changes or even successfully carrying out the experiment as described requires a clear understanding of the experimental method. 

Experimental work in physical chemistry reqrrires many complex and expensive pieces of apparatus many of these have been corrstracted specially and carmot readily be replaced. Each team should accept responsibility for its eqrripment and should check it over carefully before starting an experiment 

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Beginning students often find it useful to write a complete description of an experiment, with sections dealing with purpose, methods, results, and conclusions. Arranging a notebook to accept numerical data prior to coming to the lab is an excellent way to prepare for an experiment. It is good practice to write a balanced chemical equation for every reaction you use. This practice helps you understand what you are doing and may point out what you do not understand about what you are doing. 

If the question has not been answered, the scientist may prepare for an experiment by making a hypothesis. A hypothesis is a statement of a possible answer to the question. It is a tentative explanation for a set of facts and can be tested by experiments. Although hypotheses are usually based on observations, they may also be based on a sudden idea or intuition. 

A student prepares for an experiment involving a voltaic cell. Which of the following is needed the least to perform the experiment ... 

So let s think about how you can plan and prepare for an experiment that you have not previously done. This may be a research effort doing something new or may be carrying out an experiment that was previously reported by others. This process can be a formal one involving a written plan or a... 

It is important to skim the contents of this entire chapter, but we do not recommend that you read all parts of it in detail at this time. We make reference to specific techniques and/or apparatus as part of the procedures for many experiments thus, when you are preparing for an experiment, carefully read the appropriate sections of this chapter. This should be done prior o entering the laboratory to perform the experimental procedure ... 

As an example, reinforced concrete slabs are prepared for an experiment to compare effectiveness of arc-sprayed zinc and titanium anodes. All the slabs will be put under impressed current cathodic protection, and exposed to controlled applications of chloride to the concrete to promote corrosion of the reinforcing bar. Slabs are assigned randomly to be coated with either arc-sprayed zinc or titanium. In this case, randomization is a desirable precaution to control small inconsistencies due to mixing of the concrete, the chemical composition of the concrete, or the distribution of aggregate in the concrete. 

The most connnon commercially prepared amplifier systems are pumped by frequency-doubled Nd-YAG or Nd-YLF lasers at a 1-5 kHz repetition rate a continuously pumped amplifier that operates typically in the 250 kHz regime has been described and implemented connnercially [40]. The average power of all of the connnonly used types of Ti-sapphire amplifier systems approaches 1 W, so the energy per pulse required for an experiment effectively detennines the repetition rate. 

Time constraints ate an important factor in selecting nmr experiments. There are four parameters that affect the amount of instmment time requited for an experiment, A preparation delay of 1—3 times should be used. Too short a delay results in artifacts showing up in the 2-D spectmm whereas too long a delay wastes instmment time. The number of evolution times can be adjusted. This affects the F resolution. The acquisition time or number of data points in can be adjusted. This affects resolution in F. EinaHy, the number of scans per EID can be altered. This determines the SNR for the 2-D matrix. In general, a lower SNR is acceptable for 2-D than for 1-D studies. 

The standard curve is the plot of an instrument s readout vs. concentration, the data for which are the results of measuring a series of standard solutions prepared for the experiment. 

A sample of 25 ml prepared for an electrolysis experiment has a zinc concentration of approximately 2 x 10 8 M which leads to the passage of a current of 1.5 nA. Calculate the time necessary to deposit 3% of the Zn present. 

In a diamond cell, the sample volume is sacrificed for the sake uf higher pressures, and hence, all operations connected with (he cell have lo be performed under a microscope. In preparing the DAC for an experiment, the first step is to indent Ihe metal gasket (hardened stainless steel strip nr Inconel strip) with the anvil diamonds to the correct thickness (5(1 to UK) micrometers) and then drill a IOO- to 200-micrumeter hole as close lo the center of the indentation as possible. The gasket is seated on the face of one of the diamonds in the same orientation as it had when the indentation was made. The sample material and a small chip of ruby for pressure calibration are (lien placed in the hole. Finally, to maintain hydrostatic pressure the hole is tilled with a tiny drop of fluid from a syringe and then (he hole is quickly sealed by (he diamond fucus before Ihe fluid evaporates. 

Nitrous Acid, (a) Dissolve 0.5 gram of sodium nitrite in 5 cc. of ice water and add 1 cc. of cold 6 N H2S04. A blue solution results which at 0° effervesces very slowly. Add a few drops of this solution to a half test tube of water containing a few drops of iodide-starch solution. An intense blue color is produced. Add a few drops of sodium nitrite solution alone, of sulphuric acid alone, and of nitric acid alone to tubes made up with a similar amount of iodide-starch, and note that in none of these cases is any color produced. (To produce no effect the nitric acid must be free from nitrous acid and it should be taken from a special bottle prepared for this experiment.)... 

Take the time to organize your information with a table of contents—a table listing all experiments and the pages in which they are documented—so that the information can be easily retrieved when the company puts together a submission or prepares for an FDA inspection. 

The first entries for an experiment represent the student s preparation and are made before coming to the laboratory. The descriptive paragraphs and Erections of the manual should be studied, with particular attention to the cautions for handling dangerous materials. The lecture notes and textbook should be consulted about the topic covered by the experiment. The following information is then entered in the notebook ... 

Now that you know how to calculate the molarity of a solution, how do you think you would prepare 1 L of a 1.50M aqueous solution of sucrose (C12H22O11) for an experiment A 1.50M aqueous solution of sucrose contains 1.50 moles of sucrose dissolved in a liter of solution. The molar mass of sucrose is 342 g. Thus, 1.50 moles of sucrose has a mass of 513 g, an amount that you can measure on a balance. 

To prepare the AFM setup for an experiment, the laser must be aligned, followed by the adjustment of the photodiode position, the mounting of the sample, and finally the crude and fine approach of the tip toward the sample surface. 

To prepare the set up for an experiment, the sample should be mounted. For this purpose, we remove optical head, after driving the stepper motor upward to protect the tip and the sample from unintended contact. The sample (mounted to the sample puck see Sect. 2.2.2) is placed on the piezo scanner in center position. Finally, the optical head is placed again carefully on scanner (please ensure that the tip is far from the sample) and, with utmost care, is secured with the springs (for warning see above). 

In preparation for the experiments, the library components were removed from the bead by exposing it to trifluoroacetic acid vapor for 30 min. After the cleavage reaction was complete an internal standard was added together with the matrix solution for the laser desorption. The matrix was formed around the bead within 15-30 min and MALDI-TOF analysis was performed directly from the sample well. Results are shown in Fig. 4 where a variety of peptides was monitored in addition to bradykinin, which acted as the internal calibrant. As for all MALDI experiments, it was critical that the right matrix be chosen for the analysis. After initial examinations of different matrices under a stereo microscope followed by the MALDI-TOF experiment, dihy-droxy-benzoic acid (DHP) was found to produce the largest crystals and the best results. 

A straightforward preparation for an air-stable silver carbene complex using a standard wet chemistry kit was presented. This experiment removed the tedious requirements of a carbene synthesis and allows for the inclusion of carbenes and carbene transfer agents in the undergraduate laboratory curriculum. 

One reason Saunders proposed using the set of isotopomers presented in Eq. (11.17) was for synthetic considerations. For reactants with two hydrogenic sites attached to the same atom, it is typically much simpler to prepare the DD isotopomer than it is to synthesize a compound with high abundance D in an H D compound. The HT and DT isotopomers are generally easier to prepare because the tritium is at tracer levels. Figure 11.11 shows an example [89] of the labeled reactants needed for an experiment. 

Conditions. In all practical situations where carbon deposition presents problems, the alloy surface is not in a condition comparable to that prepared for these experiments. A heavily cold-work layer will be present covered by an oxide film, which itself may have a complex composition and structure. The... 

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