Chemists solution types determined

Throughout the main text of this book standard solutions and quantities have all been expressed in terms of molarities, moles and relative molecular masses. However, there are still many chemists who have traditionally used what are known as normal solutions and equivalents as the basis for calculations, especially in titrimetry. Because of this it has been considered desirable to include this appendix defining the terms used and illustrating how they are employed in the various types of determinations. 

ANALYZER (Reagent-Tape). The key to chemical analysis by this method is a tape (paper or fabric) that has been impregnated with a chemical substance that reacts with the unknown to form a reaction product on the tape which lias some special characteristic, e.g., color, increased or decreased opacity, change in electrical conductance, or increased or lessened fluorescence. Small pieces of paper treated with lead acetate, for example, have, been used manually by chemists for many years to determine the presence of hydrogen sulfide in a solution or in the atmosphere. This basic concept forms the foundation for a number of sophisticated instruments that may pietreat a sample gas, pass it over a cyclically advanced tape, and, for example, photo-metrically sense the color of the exposed tape, to establish a relationship between color and gas concentration. Depending upon tile type uf reactiun involved, the tape may he wet or dry and it may be advanced continuously or periodically. Obviously, there are many possible variations within the framework of this general concept. 

What is it that makes an acid an acid and a base a base We first raised those questions in Section 4.5, and we now take a closer look at some of the concepts that chemists have developed to describe the chemical behavior of acids and bases. We ll also apply the principles of chemical equilibrium discussed in Chapter 13 to determine the concentrations of the substances present in aqueous solutions of acids and bases. An enormous amount of chemistry can be understood in terms of acid-base reactions, perhaps the most important reaction type in all of chemistry. 

Measuring US velocity is the only direct way of determining adiabatic compressibility. This type of measurement has opened the door to a new world of materials characterization, a world that hitherto has remained the province of specialists. Thus, US allows biochemists to determine protein hydration, food scientists to monitor changes in solid fat content, physical chemists to measure solute-solute and solute-solvent interactions, and physicians to measure cell aggregation, just to name a single use in some key areas. 

The main hazards of working with corrosives are skin exposure and inhalation. Chemists should wear gloves when working with corrosive solutions. The type of glove depends on the specific corrosive and the concentration in solution. For common acids and bases, nitrile gloves will be adequate for skin protection. A glove compatibility chart should be consulted to determine the appropriate gloves for other corrosives. Most corrosives should be handled in a chemical hood. 

There are many approaches to experimentation in a laboratory. One type that physical chemists engage in is the measurement of a known system to obtain new fundamental information about the system. These experiments are usually well planned and most of the equipment is in place before the first experiment is undertaken. High precision and attention to minute detail is essential if these works are to be worthy of completion. The kinetics of the hydrolytic degradation is such a study. The electrical conduction of solutions of condensed phosphates as a function of complexing cations and the determination of instability constants is another. The list could be almost endless and this science is usually conducted by highly trained personnel. 

However, just because the results of a set of analyses are in close agreement does not necessarily mean that the values are correct. This is because of the possibility of determinate errors. Such errors have a definite cause (although it may be unknown to the analyst), and each type of determinate error is always in the same direction. For example, if an anal5dicd chemist were using a pipet rated to deliver 25.00 mL of solution that through a manufacturing mistake actually delivered 25.35 mL, a determinate error would be introduced into the analysis in this case, it could readily be detected by calibrating the pipet. 

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