Search

This article reports on a new device, called a geyser guide, that allows for quantitative measurements of both bubble sizes and kinetics of foam production in the so-called Diet Coke and Mentos experiment. The device is easily constructed, is made using readily available materials, and allows the experiment to be carried out indoors with no mess. In contrast to previously reported measuring devices used to monitor this experiment, the geyser guide allows for tall columns of foam to be produced and visualized. This feature makes experiments with the geyser guide suitable for demonstrations in large classrooms. Investigations with the geyser guide can be tailored for use in settings that span from elementary science classrooms to undergraduate research projects. Explorations with the geyser guide have allowed for estimates that 2.4-14 million bubbles per liter of Diet Coke are produced during the experiment and that a single Mentos candy contains 50?000-300?000 nucleation sites.

A quantitative titration of the amount of magnesium hydroxide in milk of magnesia using only items purchased in grocery and retail stores is reported. Either vinegar or a solution of food grade citric acid serves as the titrant, while food dyes advertised as being extracted from natural sources provide the end-point indicator. An inexpensive, digital kitchen balance with 0.01 g resolution allows for quantitation of the amount of titrant added. Students who performed this experiment either in class or remotely generally determined amounts of magnesium hydroxide in milk of magnesia that were within 10% of that claimed by the manufacturer. That easily obtained materials are used in this activity makes it amenable for experimentation in remote settings. The use of both the natural food dyes and inexpensive digital balance opens a wide swath of possibilities for new experiments to be developed for at-home experimentation.

Carbonated beverages have long provided chemical educators and other teachers of science with an easy-to-obtain system that connects to several physicochemical concepts. For example, many educators have devised experiments to determine the pressure of CO[subscript 2] contained in commercial carbonated beverages, but the role of temperature in such measurements has not been explored in detail. The experiments presented here describe a simple way to measure the pressure of CO[subscript 2] in carbonated beverages, and how to convert such pressures measured at different temperatures to a standard value so that comparisons of measurements obtained at different temperatures can be made. The results provide insights into other experiments that involve carbonated beverages.

The so-called Diet Coke and Mentos experiment is initiated by dropping Mentos candies into a bottle of Diet Coke or other carbonated beverage. This causes the beverage to rapidly degas, causing foam to stream out of the bottle. Simple application of the gas laws leads to the straightforward prediction that ejection of greater foam volume is expected at lower atmospheric pressure. This hypothesis is bolstered when principles of bubble physics are taken into account. This hypothesis was tested and confirmed by monitoring the foam produced during the Diet Coke and Mentos experiment at various altitudes above sea level. Upon further application of the aforementioned principles, a relationship between degassing kinetics, beverage CO[subscript 2] concentration, and the size of pores on the candy surface that serve as nucleation sites can be derived. Using this relationship and experimental measurements of degassing kinetics, students estimated that the nucleation sites on Mentos candies are on the order of 2-7 [mu]m in dimension. Students in Physical Chemistry, General Chemistry, and nonmajors' courses have found these experiments to be of great interest.

When Mentos candies are dropped into a bottle of Diet Coke, a foamy fountain jets out of the beverage container. It has previously been argued that ingredients found in Mentos candies significantly enhance this fountaining effect. Other previous work has demonstrated that the kinetics of foam production can be quantitatively monitored using a device constructed from inexpensive, easily obtained materials. In the results reported here, students used this simple device to monitor the kinetics of foam production in the Diet Coke and Mentos experiment and to draw conclusions about the system. It was possible to model the kinetic data obtained using kinetic mechanisms that involve irreversible first-order steps. Furthermore, the data collected allowed students to acquire evidence that the kinetics of foam production appears to be unaffected by the presence of certain ingredients in candies and gums, in contrast to previous claims. Many of the protocols described herein can be carried out simply and inexpensively, making them useful for high school, introductory, and general chemistry courses. In addition, the kinetic data collected are of sufficient quality to allow for analysis sophisticated enough for use in student research projects and physical chemistry courses.

An experiment is described that uses easily obtained materials (glow sticks, chalk, and acetone or alcohol) to separate the dyes contained in glow sticks that actively emit chemiluminescent light. The experiment is very easy to carry out, making it amenable for students to perform in laboratory or outreach settings. The separation occurs fast enough that the experiment can be conducted as an in-class demonstration.

The separation of chamazulene from hydrophilic contaminants present in blue tansy oil provides a visually engaging example of two common techniques: extraction and thin-layer chromatography (TLC). This application uses liquid CO[subscript 2] as a lipophilic solvent to pull a brilliant blue hydrocarbon molecule, chamazulene, out of or through a common hydrophilic material, cellulose. Yellow-green, hydrophilic components remain in a cotton ball or at the lower end of a paper strip. In dramatic fashion, the separation of colored components of blue tansy oil is accomplished with an environmentally sustainable solvent, CO[subscript 2], and an innocuous support material, cellulose. We believe this is the first reported use of liquid CO[subscript 2] in centrifuge tubes to conduct TLC.

When carbonated beverages (which are supersaturated solutions of aqueous carbon dioxide) are confined within a narrow-necked container, events which rapidly release the gas from solution produce a fountain out of the beverage. One well-known variant of this experiment is the addition of Mentos candies to a bottle of Diet Coke. Previous reports have shown that the presence of aspartame and benzoate in carbonated beverages enhance the fountaining effect. These additives are thought to enhance fountaining by lowering the surface tension of the beverage, but the details of this process are not completely understood. This paper explores the relationship between geyser height and the type of carbonated beverage. It is shown herein that several other compounds commonly found in commercial carbonated drinks such as sucrose, glucose, citric acid, and components of natural flavors also enhance geyser heights. By examining how these additives affect bubbling and foaming behavior in seltzer water, it is postulated that solutes which inhibit bubble coalescence contribute to higher fountains.

A very simple protocol for teaching Beer's Law and absorption spectrophotometry using a smart phone is described. Materials commonly found in high school chemistry laboratories or even around the house may be used. Data collection and analysis is quick and easy. Despite the simple nature of the experiment, excellent results can be achieved.

An activity is described wherein students observe dynamic floating and sinking behavior of plastic pieces in various liquids. The liquids and solids are all contained within a plastic bottle; the entire assembly is called a "density bottle". After completing a series of experiments that guides students to think about the relative densities of both the liquids and solids in the bottle, students are able to explain the curious floating and sinking phenomena. As a part of the activity, students construct their own bottles and are encouraged to describe to others how the density bottle works. These bottles can be constructed using inexpensive and easily obtained materials. The level of inquiry involved in the activity can be tailored to meet the particular interests and needs of students. Modifications to the density bottle, including an engaging one that uses LEGO pieces, are discussed.

Everyone enjoys seeing the cloudy white fog generated when solid carbon dioxide (dry ice) is placed in water. Have you ever wondered what physical and chemical processes occur to produce this fog? When asked this question, many chemical educators suggest that the fog is produced when atmospheric water vapor condenses on cold carbon dioxide gas that sublimes through the water. But this explanation is incorrect, as shown by Luck and co-workers in an article previously published in "J. Chem. Educ." Herein, we extend this previous work by presenting some simple experiments and explanations that provide a model for how the fog forms when dry ice is placed in water. Many of these experiments can be carried out using materials found at the pharmacy, grocery store, or hardware store. The explanations involved draw from many concepts taught in general chemistry such as vapor pressure and Le Cha^telier's principle.

Coulometric titrations involve the quantification of analyte by measurements of current and time. In most coulometric titrations, the anode and cathode are placed in isolated cells that are connected by a salt bridge. By contrast, the experiments described here involve coulometric titrations (of acidic protons in solution) using a silver anode and graphite cathode placed in the same reaction vessel. The chemistry of the electrode reaction generating the reactant is described. This use of non-isolated electrodes allows for simplified experimental procedures (some of which are described) and faster titration times. Additional streamlining of the experiment is achieved by the use of MicroLab data acquisition instrumentation. This laboratory is appropriate for an analytical course. (Contains 4 figures.)

We believe that students should have opportunities--early and often--to learn about science and math activities in fun and recreational ways. As a result, we try to provide many science enrichment activities to the surrounding community. In doing so, we hope to inspire young students to become future scientists and mathematicians. Here we describe some annual science outreach events that we have hosted, share a few demonstrations and activities we have tried at these events, and discuss how we plan to connect our outreach in 2011 to the themes of the International Year of Chemistry. (Contains 4 tables and 3 figures.)

A data set of 7,381 molecular iodine vapor rovibronic transitions between the X and B electronic states has been prepared for an advanced undergraduate spectroscopic analysis project. Students apply standard theoretical techniques to these data and determine the values of three X-state constants (image omitted) and four B-state constants (image omitted). Morse potentials for the two states may be calculated from these seven constants. (Contains 1 table and 1 figure.)

An exercise is presented in which the kinetics of the irreversible "reaction" of pennies in the heads-up state to pennies in the tails-up state is simulated by a hands-on, Monte Carlo approach. In addition, the exercise incorporates a second simulation in which the irreversible "reaction" of dice with a red face uppermost to a blue face uppermost is conducted. The transition states of the reactions are assumed to be a penny that is in the process of being flipped or a die in the process of being rolled, respectively. Data collected by students who perform these simulations show that both "reactions" follow first-order decay kinetics. Arrhenius plots from these data yield activation energies comparable to assigned values and pre-exponential factors close to what would be expected based on the probability of a "reactant" achieving the correct orientation for conversion into "product". A comparison of the values obtained for the pre-exponential factors for the different simulations allows students to semi-quantitatively discuss the orientational requirement that is contained within this factor. (Contains 3 figures.)

Experiments designed to teach students how movie actors can survive being on fire during movie scenes are described. The insulating properties of a gel made of a super absorbent polymer and water are also discussed.

Michael Sanger previously described methods of conducting flame tests with household items. This activity was used in outreach settings, and was extended in a variety of ways. Large-scale strontium (red), copper (green), and carbon (blue) flames were described using household items, helping children investigate the chemistry of sparklers and colored flame birthday candles.

An option for conducting experiments in cyclic voltammetry using a MicroLab model 290 sensor adaptor module and MicroLab FS-522 general purpose laboratory interface is described. This system is demonstrated on a tetramethyl-p-phenylenediamine solution.

The separation of the contents of an activated lightstick using a chromatography column is described. The experiment teaches the role played by intermolecular forces in the separation of components from a mixture and is applicable for teaching students at all levels.

A hands-on activity and demonstration, both applicable to the 2010 National Chemistry Week theme of Behind the Scenes with Chemistry, are presented. In the activity, students compare and contrast the properties of heat conductors and heat insulators. During the demonstration, students learn that water absorbed by a superabsorbent polymer can insulate material from a burning flame. Students also learn about Gary Zeller, a chemist who won an Academy Award for scientific achievement in 1988 for his invention of Zel Jel. Zel Jel is a mixture of water and polymers that is used in the special effects industry to protect actors from being burned when they are set on fire during filming. (Contains 2 notes and 1 figure.)

A classroom activity where the rebound height of a racquet ball is tested over a wide temperature range is described. The activity is a good way to teach glass transition temperature of amorphous polymers.

Separation of glow stick dyes adhered to a cotton swab using liquid CO2 provides an engaging demonstration of several chemical concepts including polarity, kinetics, chemiluminescence, and the importance of CO2 a green solvent. The simple protocol allows access to a broad range of students. Differential polarities of the glow stick dyes allow certain dyes to be preferentially dissolved in liquid CO2, leaving other dyes adhered onto cotton. Both TCPO (bis(2,4,6-trichlorophenyl)oxalate) and H2O2, which together provide the necessary reaction for chemiluminescence, are present in both the extracted liquid and cotton upon dissipation of CO2. Thus, it is possible to compare the emission spectrum of the extracted fluid to that of the original glow stick and the residue left on the cotton swab. Emission peaks resulting from the presence of polar dyes in the original glow stick and on the cotton are routinely observed to be missing in the extracts. [ABSTRACT FROM AUTHOR]

The separation of chamazulene from hydrophilic contaminants present in blue tansy oil provides a visually engaging example of two common techniques: extraction and thin-layer chromatography (TLC). This application uses liquid CO2 as a lipophilic solvent to pull a brilliant blue hydrocarbon molecule, chamazulene, out of or through a common hydrophilic material, cellulose. Yellow-green, hydrophilic components remain in a cotton ball or at the lower end of a paper strip. In dramatic fashion, the separation of colored components of blue tansy oil is accomplished with an environmentally sustainable solvent, CO2, and an innocuous support material, cellulose. We believe this is the first reported use of liquid CO2 in centrifuge tubes to conduct TLC. [ABSTRACT FROM AUTHOR]

Information about a method used for quantitative determination of carbon dioxide inside carbonated beverages without opening the container is provided. This method uses a combination of Henry's law and freezing point depression measurements. A black electric tape was used to attach MicroLab thermistor sensors to the outside of unopened cans of LaCroix brand sparkling water.