This experiment describes a simple protocol for teaching acid–base titrations using potentiometry, conductivity, and/or photometry to determine end points without an added indicator. The chosen example examines the titratable acidity of a red wine with NaOH. Wines contain anthocyanins, the colors of which change with pH. Importantly, at the equivalence point, anthocyanins maintain their color, and this effect can be captured optically using a desktop scanner. RGB-based color values are obtained from the digitized images using a dedicated application and employed to generate plots of |v| versus titrant volume. The end point is the point at which the slope (d|v|/Δ/dV) of the titration curve is at a maximum; (d|v| is a vector expression of the color change). The photometric titrations were carried out using a plastic 96-well immunology plate and a flat-bed scanner, and RGB values were extracted simultaneously from all 96 wells in less than 5 min from the images using the ImageJ plugin “ReadPlate”. The wine was also titrated using conventional potentiometric and conductometric techniques, and methods were compared using F-test, t-test, and one-way ANOVA. The potentiometric titration yields pH versus titrant volume curves, and the equivalence point is where the slope, or the slope of the derivative curve (dpH/dV), is greatest. The conductometric titration yields conductivity versus titrant volume curves, and the end point is determined as the volume where the slope exhibits a marked change. All titration and derivative curves were plotted and analyzed using spreadsheet software.

A complete ecosystem consists of the geosphere (earth), hydrosphere (water), atmosphere (air), and biosphere (life). The essential elements exist in different forms in each sphere and pass between them by chemical and physical processes called biogeochemical cycles. Students are initially introduced to these concepts in grades 4À6, but do not usually study them intensively until secondary environmental science classes. 1 Incorporating games into a class (or lab) is a nonthreatening way to refresh a student's memory, and the interactive format provides a stimulating environment in which to reinforce important concepts. Such games have been developed to address a wide variety of chemical concepts. 2 "Element Cycles" is a simple board game designed to familiarize students in grades 4À12 with the most common essential elements and their roles in the environment. The students initially gain knowledge about the elements and their biogeochemical cycles by researching them online. This knowledge is then reinforced by constructing a game board with ecological sections and element cards to pass the elements between ecosystems. When the students play the game and are passed from ecosystem to ecosystem, the forms of the elements change and they gain greater appreciation of the cyclic nature of matter in the environment.The game can be customized for different grade levels. For elementary students, the ecosystems can be defined as earth, air, water, and life, and the forms of the elements are simply the names of the compounds and ions, such as carbonate rocks, carbon dioxide gas, nitrogen gas, and so forth. For more advanced students, the ecosystems are defined as geosphere, atmosphere, hydrosphere, and biosphere, the forms of the elements are the actual chemical formulas, such as CO 3 2À , CO 2 , and N 2 , and mechanisms of transformation can be included, such as oxidation, reduction, precipitation, and so forth.This game format is also adaptable to other chemical concepts and is an entertaining alternative to rote memorization of specific facts. One example of such a concept is solubility. The four sections of the board can be labeled as þ1 cations, À1 anions, þ2 cations, and À2 anions. The track is then marked with appropriate anions and cations, and when the student lands on a symbol, he or she is sent to an oppositely charged ionic section and must draw a specific ion card and correctly predict solubility. Other units, such as oxidationÀreduction, are also potential game topics. ' MATERIALS• List of essential elements for students to research: The suggested minimum is C, N, P, and S, but the list may also be expanded to include O and H. Some good references, in ABSTRACT: "Element Cycles" is an activity designed to reinforce correlation of essential elements and their different forms in the ecosystem. Students are assigned essential elements to research as homework, then share results, and construct game boards with four ecosphere sections: geosphere (earth), hydrosphere (water), atmosphere (air), and biosphere (life). Th...

No abstract

No abstract

No abstract