Microscale experiments

A demonstration of potentiometry with a silver electrode (or a microscale experiment for general chemistry) is described by D. W. Brooks, D. Epp, and H. B. Brooks, Small-Scale Potentiometry and Silver One-Pot Reactions, ... 

This chapter presents a review of the progress relating flammability measurements and properties deduced from microscale experiments of milligram size samples with measurements obtained from mesoscale experiments of sample size about 100 g. We present a comprehensive and integrated approach based on sound scientific method, yet practical for assessing the flammability of nanocomposite polymers in the early stage of their formulations where only milligram order quantities are available. Our approach does not extend to quantum chemistry or molecular dynamics to... 

A methodology and a new parameter have been developed to quantify the effect of the nanoparticles in reducing the mass loss rate in the mesoscale experiments (i.e., cone) where all other properties have been determined from the microscale experiments. 

The differences in concentration between the micro- and macroscale experiments also affect the separation of the waves. The waves of irreversibly reduced compounds cover a greater potential range at higher concentrations than at lower concentrations. A reduction which in the microscale experiments gives two separate reduction waves may be difficult to carry out as a selective reaction. The best way to get a partial reduction in such a case is to use a potential at the foot of the composite wave. 

Ibanez, J. G. Miranda, C. Topete, J. Garcia, E. Metal Complexes and the Environment Microscale Experiments with Iron-EDTA Chelates, Chem. Educ. 2000, 5, 226-230. http //joumals.springemy.com/chedr/... 

Ibanez, J. G. Redox Chemistry and the Aquatic Environment Examples and Microscale Experiments, Chem. Educ. Int. (IUPAC) 2005,6,1-7. Jackson, G. B. Applied Water and Spentwa-ter Chemistry. A Laboratory Manual, Van Nostrand-Reinhold New York, 1993. 

Ibanez, J. G. Mena-Brito, Rodrigo Fregoso-Infante, Arturo Seesing, M. Tausch, Michael W. Photoreactions with Titanium Dioxide— A Microscale Experiment, Prax. Naturwiss. Chem. Sch. (Germany) 2005, 54(3), 22-24. 

Carrying out a fractional distillation on the truly micro scale (< 1 mg) is impossible, and even impossible on a small scale (10-400 mg). In the present microscale experiment the distillation will be carried out on a 4-mL scale. As seen in later chapters various types of chromatography are employed for the separation of micro and semimicro quantities of material while distillation is the best method for separating more than a few grams of material. 

To the extent possible, all chemistry labs should convert to microscale experiments. This is the single most productive way to avoid the generation of significant wastes and to minimize student exposure. Experiments using toxic substances can often be conducted with alternative reagents [bleach instead of chromium (VI) for oxidation, for example]. 

Organic Chemistry Laboratory with Qualitative Analysis Standard and Microscale Experiments [17] 29 45 29... 

Bell C E Jr. Taber D F, Clark A K (2001) Organic chemistry laboratory with qualitative analysis Standard and microscale experiments 3rd ed. Thomson Brooks/Cole. 

R. L. Blankespoor and K. Piers,/. Chem. Educ., 68, 693 (1991), Hydroboration-Oxidation of (lR)-( + )-a-Pinene to Isopinocampheol A Microscale Experiment that Displays Regio-and Stereochemistry Using NMR Spectroscopy and Molecular Mechanics Calculations. 

A student conducts a microscale experiment to determine the solubiUty of ammonium chloride, NH4CI. With 0.050 g of the salt in a small test tube, the smdent has to add 1.50 mL of water to dissolve all of the solid. Based on this experiment, assuming a density of 1.0 g/mL Ibr water, calculate the solubility of ammonium chloride per 100 g of H2O. 

Microscale experiments decrease costs, consumption of reagents, and generation of waste. A student buret can be constructed from a 2-mL pipet graduated in 0.01-mL intervals. Volume can be read to 0.001 mL and titrations can be carried out with a precision of 1%. 

With this final word of caution and advice, we hope you enjoy the learning experience you are about to begin. Learning the care and precision that microscale experiments require may seem difficult at first, but before long you will be comfortable with the scale of the experiments. You will develop much better laboratory technique as a result of microscale practice, and this added skill will serve you well. 

Special care must be taken when working with small amounts of liquid or solids. In the typical microscale experiment, a student will use from 10 to 1000 mg of a liquid or solid. Specially designed microscale equipment will be used for these small-scale reactions. You may not be used to working with such small quantities, but after a while you will adjust to "thinking small."... 

Liquid reagents and solutions are added to a reaction by several means, some of which are shown in Figure 7.9. For microscale experiments, the simplest approach is simply to add the liquid to the reaction by means of a Pasteur pipette. This method is shown in Figure 7.9A. In this technique, the system is open to the atmosphere. A second microscale method, shown in Figure 7.9B, is suitable for experiments in... 

This filtration technique is most useful when the solid material being filtered from a mixture is to be collected and used later. The filter cone, because of its smooth sides, can easily be scraped free of collected solids. Because of the many folds, fluted filter paper, described in the next section, cannot be scraped easily. The filter cone is likely to be used in microscale experiments only when a relatively large volume (greater than 10 mL) is being filtered and when a Hirsch funnel (Section 8.3) is not appropriate. 

For microscale procedures, a 60- or 125-mL separatory funnel is recommended. Because of surface tension, water has a difficult time draining from the bore of smaller funnels. Funnels larger than 125 mL are simply too large for microscale experiments, and a good deal of material is lost in "wetting" their surfaces. 

With microscale experiments, the mixture may be transferred to a centrifuge tube. The emulsion will often break during centrifugation. Remember to place another tube filled with water on the opposite side of the centrifuge to balance it. The two tubes should weigh the same. 

Microscale Inverted Capillary Method. In microscale experiments, there often is too little product available to use the semimicroscale method just described. However, the method can be scaled down in the following manner. The liquid is placed in a 1-mm melting-point capillary tube to a depth of about 4-6 mm (see Figure 13.4B). Use a syringe or a Pasteur pipette that has had its tip drawn thinner to transfer the liquid into the capillary tube. It may be necessary to use a centrifuge to transfer the liquid to the bottom of fhe tube. Next, prepare an appropriately sized inverted capillary, or bell. 

An alternative, which is applied conveniently in microscale experiments, is to remove the colored impurity by column chromatography. Because of the polarity of the impurities, the colored components are strongly adsorbed on the stationary phase of the column, and the less polar desired product passes through the column and is collected. 

---