Acids and bases are chemical compounds always present in our daily life. They are important raw materials in manufacturing industries and are necessary for the control of various industrial processes. They participate actively in living organisms’ metabolism and, if improperly disposable they can alter the environmental conditions necessary to the human well-being. Acids have sour taste (e.g. citrus fruits), while bases have astringent flavors (“soap like”). In addition, theses substances are part of cosmetic formulations, food, drinks, pharmaceuticals, cleaning products, toiletries, etc.. The most common way to determine the acidity or alkalinity of an aqueous solution is measuring its pH, but this concept is not as simple as it seems to be.

Keywords
acids, bases, acid-base theories, pH, the concept of pH, pH scale, acidity, alkalinity.

Authors
João Carlos de Andrade
Universidade Estadual de Campinas, Instituto de Química

The Chemical and physical phenomena and the principles applied in qualitative analysis to identify ions in aqueous solution are the same ones used in quantitative analysis of different samples and are still used in many official reference methods, including instrumental methods or procedures. This shows the importance of knowledge of the fundamentals of qualitative analysis, requiring the teacher to get the students’ attention for their practical applications. Below are some brief descriptions of methods and procedures as suggestions for class discussion.

Keywords
qualitative analytical chemistry, quantitative analytical chemistry, concepts, applications, experiments, learning, testing methods, ASTM, AOAC, RSC.

Authors
João Carlos de Andrade
Universidade Estadual de Campinas, Instituto de Química
Terezinha Ribeiro Alvim
Centro Federal de Educação Tecnológica de Minas Gerais, Departamento de Química – CEFET-MG

Obeying the fundamental law of nature that says, “a physical or chemical system always tends to cause an irreversible change from some state of initial non-equilibrium to a final equilibrium”, chemical reactions can be defined as processes in which different substances interact with each other, with a rearrangement of atoms occurring that completely changes the initial characteristics of the substances involved, tending to an equilibrium. This article shows, in a concise manner, the kinetic and thermodynamic aspects of equilibrium in aqueous solution.

Keywords
equilibrium, electrolytes, activity, activity coefficient, ionic strength, Debye-Hückel, kinetics, thermodynamics.

Author
João Carlos de Andrade
Universidade Estadual de Campinas, Instituto de Química

The content of Inorganic Qualitative Analytical Chemistry usually used by Brazilian Higher Education Institutions (HEIs) covers the theory of chemical equilibrium in aqueous solution and, in the laboratory, the separation and identification of cations and anions in solution or solid samples, using classical methods. As there are still opinions both fory and against the maintenance of classic Qualitative Analytical Chemistry in the curriculum of Brazilian higher education in chemistry, this section intends to provide evidence demonstrating of the importance of teaching about research of cations and anions in the formation of chemists in Brazil, as a fundamental basis for the teaching of Quantitative Analysis and Instrumental Analysis.

Keywords
Qualitative Analytical Chemistry, data collection, formation of chemists, cation separation reactions, cation identification reactions, anion identification reactions, analytical steps, reaction medium, operational care, Pedagogy.

Authos
João Carlos de Andrade
Universidade Estadual de Campinas, Instituto de Química
Terezinha Ribeiro Alvim
Centro Federal de Educação Tecnológica de Minas Gerais, Departamento de Química – CEFET-MG

History shows that nothing is totally new and therefore the old should not be discarded, but known so that new knowledge can be constructed. Thus, when interviewed by Rudy M. Baum, Henry Taube, Nobel Prize in Chemistry in 1983, said that the disappearance of qualitative analysis from the curriculum of American universities was a mistake, because that was a way to introduce descriptive chemistry and motivate students to study chemical reactions that, in his opinion, “are the heart of chemistry” [1]. In view of this controversy and of the possible options for the use of the discipline of Qualitative Analytical Chemistry as a tool for the education of chemical equilibrium in aqueous solution, a critical view of the historical sequence of the procedures for qualitative analysis development is presented below.

Keywords
classical analysis, Qualitative Analytical Chemistry, education, history, applications.

Authors
João Carlos de Andrade
Universidade Estadual de Campinas, Instituto de Química
Terezinha Ribeiro Alvim
Centro Federal de Educação Tecnológica de Minas Gerais, Departamento de Química – CEFET-MG

Some analytical techniques, such as voltammetry, are relatively little used in undergraduate experimental disciplines in chemistry (and related sciences), although addressed in theoretical ones. Since, in contrast to what one thinks, voltammetric measurements are still often used in routine analysis, some of the most direct techniques will be highlighted in this text, with suggestions to the reader who seeks more knowledge on this theme. The experiments presently proposed present a well defined conceptual and methodological character and have been tested in the experimental classes of the Instrumental Analytical Chemistry discipline of the Institute of Chemistry at UNICAMP. Each module is proposed for four hours of activities in the laboratory, with low risk.

Keywords
voltammetry, water, sugarcane liquor, fruit juices, nickel, cobalt, copper, cadmium, zinc, ascorbic acid

Authors
João Carlos de Andrade
Audrey de Arruda Falcão
Elaine Castilho Guedes
Universidade Estadual de Campinas, Instituto de Química

Translated by
João C. de Andrade

Revised by
Carol H. Collins

Warning

Attention: “Read carefully the procedure before starting the experiment. Do not perform the experiment without being monitored by your teacher. In doubt ask for help!”

Besides conceptual and quantitative aspects, studies in chemistry should involve experiments with a demanding high level of care and attention in the use of experimental techniques. Considering these aspects, the determination of the molar mass of a metal, through the volume of gas released by its reaction with an acid, is an ideal experiment to achieve these purposes. This work addresses important concepts such as the “molar mass” and the “standard electrode potential”, through accurate results obtained by using simple experimental techniques such as weighing, measuring volumes and the preparation of solutions. The first didactic experiment used to discuss and contextualize these concepts in a single experiment was published in 1937 in the Journal of Chemical Education, although the reaction of magnesium with different acids had already been discussed (in terms of the Bronsted-Lowry’s acids theory) in 1931, in this same journal. Some highlighted words in the text are listed in the Glossary of Terms, Definitions and biographies, annexed to the main text.

Keywords
reaction of metal with acid, stoichiometry, law of ideal gases, determination of molar mass, standard electrode potential, weighing, volume measurement, preparation of solutions

Authors
Janaína César
João Carlos de Andrade
Universidade Estadual de Campinas, Instituto de Química

Translated by
João C. de Andrade

Revised by
Carol H. Collins

Warning

Attention: “Read carefully the procedure before starting the experiment. Do not perform the experiment without being monitored by your teacher. In doubt ask for help!”

This work presents a discussion about the characteristics of supercritical fluid extraction, its operational conditions, a comparison with other extraction techniques and analytical applications of this technique. The text shows that a supercritical fluid can be obtained with different substances if they are above their critical point, the critical temperature and critical pressure, which can be viewed as a phase diagram. Among the most used supercritical fluids is carbon dioxide due to its low critical parameters, and because it is not toxic, not flammable and inert. Also, in addition to being gaseous at room temperature, it is highly accessible, easily obtainable with a high degree of purity at low cost and it can still be modified by the addition of organic solvents. The extraction operation with a supercritical fluid also permits on-line couplings and the recovery of the solvent used. The parameters governing SFE are discussed, particularly pressure, temperature, the nature of the matrix and the polarity of the extractor fluid. Some points of comparison show that extraction with a supercritical fluid is an attractive technique to be applied in the preparation of solid samples, since it has advantages compared to other alternative sample preparation techniques (Soxhlet, ultrasound, accelerated solvent extraction, among others). Among those are the speed of the extraction process, its low cost per extraction, the reduced consumption of organic solvents, fewer handling procedures, good precision and accuracy, versatility, good recovery and ease of automation. This text also presents some applications of SFE, which are many and varied, including environmental samples (soil, water, air, sediment and suspensions), food (fruits, vegetables, cereals, animal tissues, etc), natural products (essential oils, flavorings, etc), drugs (drugs of abuse, hormones, etc) and polymers.

Keywords
extraction, supercritical fluid, Analytical Chemistry, fluid extractor, chromatography

Autores
Glaucia M. F. Pinto
Pontifícia Universidade Católica de Campinas, Faculdade de Química
Jefferson F. Pinto
Protimu Ltda
Isabel C. S. F. Jardim
Universidade Estadual de Campinas, Instituto de Química

Translated by
João C. de Andrade

Revised by
Carol H. Collins

This is a support text to the Quantitative Analysis by Chromatography multimedia application available in Applications and Programs. As its purpose is to provide the same material in printed form to the reader, this text is more detailed than that presented in the application, although with a smaller number of figures. It is also an alternative way to present the information, serving either as a supporting material or as a resume of to the original multimedia application.

Keywords
chromatography, calibration curve, data processing, mean, median, confidence intervals, rejection of data, Huber test, internal standard, external standard

Authors
Antônio Luiz Pires Valente (in memoriam)
Cássio Ricardo Fares Riedo
Fabio Augusto
Universidade Estadual de Campinas, Instituto de Química

Translated by
João C. de Andrade

Revised by
Carol C. Collins

This text will introduce the main voltammetric methods of analysis, from its basic aspects to applications in trace analysis. The techniques to be presented are continuous current (polarographic; DC, direct current), sampled direct current (sampled DC), normal pulse (NP, normal pulse), differential pulse and square wave voltammetry. The use of voltammetry in trace analysis is discussed using anodic / cathodic stripping and adsorptive stripping voltammetry. Aspects related to the matrix effects and to method validation will also be discussed.

Keywords
polarography, voltammetry, anodic stripping voltametry, cathodic stripping voltametry, adsorptive stripping voltammetry, matrix effects, method validation

Autor
Luiz Manoel Aleixo (in memoriam)
Universidade Estadual de Campinas, Instituto de Química

Translated by
João C. de Andrade

Revised by
Carol H. Collins