Erasing the Glow in the Dark: Controlling the Trap and Release of Electrons in Phosphorescent Materials
William A. Getz, Dannielle A. Wentzel, Max J. Palmer, and Dean J. Campbell; J. Chem. Educ., 2018, 95 (2), pp 295–299.
The authors use fluorescence spectroscopy to demonstrate the darkening effect using lower energy wavelengths on the intensity of the fluorescent light and the time until the emission is quenched. A zinc sulfide phosphor doped with Cu metal is excited by a 405 nm LED, and the fluorescence spectrum is observed. In a second trial, after the excitation, a 650 nm red laser light is shined on the phosphor. The intensity of the fluorescence spectrum is diminished and the length of time that the light is emitted is reduced. Connections to understanding how electrons move from the valence band to the conduction band and back are made in the article. It also discusses the kinetics of the changes observed as they relate to temperature and activation energy. A Vernier SpectroVis Plus spectrophotometer and Optical Fiber were used to observe the spectra produced.
Adapting Three Classic Demonstrations To Teach Radiant Energy Trapping and Transfer As Related to the Greenhouse Effect
Dwayne A. Bell and Jesse C. Marcum; J. Chem. Educ., Articles ASAP (As Soon As Publishable).
The authors address three fundamental concepts that are part of students’ understanding of the greenhouse effect and global climate change; the existence of infrared radiation, absorption of IR by greenhouse gases, and steady-state energy flow.
To demonstrate the existence of infrared radiation, the authors used a Pyranometer to measure the level of irradiance at one centimeter increments along a rainbow spectrum they produced from a 300 W theatrical light. They were able to show that there was energy being produced from the light bulb, even though the pyranometer was placed in a part of the spectrum that appears black to the naked eye.
The authors also discuss their demonstrations of how carbon dioxide molecules are energetically excited and vibrate in the presence of infrared light by using models of the molecules constructed from balls and springs. They also model how energy flows through a system using a plastic water-flow device with changeable partitions to mimic the addition or removal of carbon dioxide from the atmosphere.
Demonstrations of Magnetism and Oxidation by Combustion of Iron Supplement Tablets
Max J. Palmer, Keri A. Martinez, Mayuresh G. Gadgil, and Dean J. Campbell; J. Chem. Educ., 2018, 95 (3), pp 423-427.
The authors demonstrate the conversion of iron(II) ion in iron nutrient supplements to hematite by first heating a sample with a torch. They compare the products of heating a supplement to those produced by heating iron(II) sulfate heptahydrate. The second compound produces magnetite and maghemite, which have a stronger attraction to a magnet than hematite. The strength of the magnetic fields is measured and compared using a Magnetic Field Sensor and LabQuest 2.
Nanoparticle Synthesis, Characterization, and Ecotoxicity: A Research-Based Set of Laboratory Experiments for a General Chemistry Course
Zoe N. Amaris, Daniel N. Freitas, Karen Mac, Kyle T. Gerner, Catherine Nameth, and Korin E. Wheeler; J. Chem. Educ., 2017, 94 (12), pp 1939–1945.
Students learn to synthesis silver nanoparticles and then characterize them using UV-VIS spectroscopy and dynamic light scattering. The particles are easily synthesized with readily available reagents. To measure the spectrophotometric properties, the students used a Vernier UV-VIS Spectrophotometer. Green chemistry principles are followed during the course of this experiment.
Speciation and Determination of Low Concentration of Iron in Beer Samples by Cloud Point Extraction
Lida Khalafi, Pamela Doolittle, and John Wright; J. Chem. Educ., 2018, 95 (3), pp 463-467.
Students determine the concentration of iron in beer samples. They learn how to extract the iron and then complex it so that the concentration can be determined using the Beer-Lambert relationship. They set up standards and use absorbance spectroscopy to determine the concentration of iron in the original beer sample. Vernier SpectroVis Plus Spectrophotometers were used in this experiment.
Determining the Speed of Sound and Heat Capacity Ratios of Gases by Acoustic Interferometry
Thomas D. Varberg, Bradley W. Pearlman, Ian A. Wyse, Samuel P. Gleason, Dalir H. P. Kellett, and Kenneth L. Moffett; J. Chem. Educ., 2017, 94 (12), 1995–1998.
The authors describe a method to determine the speed of sound and heat capacity through various gases. They use a microphone and white noise apparatus connected to a sound cavity, which is a long, plastic tube. The data is collected and analyzed on an Apple iPad. They refer to work done in this same area by others using Vernier LabPro and LabQuest 2.
Because the tube has a fixed length, when the white noise is introduced into the tube, an interference pattern is generated and plotted. Students can apply a Fourier transform to determine the frequency spectrum of the standing waves in the tube.
Studying Intermolecular Forces with a Dual Gas Chromatography and Boiling Point Investigation
William Patrick Cunningham, Ian Xia, Kaitlyn Wickline, Eric Ivan Garcia Huitron, and Jun Heo; J. Chem. Educ., 2018, 95 (2), pp 300–304.
The authors describe two laboratory experiences they have developed for their students to study the difference in structure and intermolecular forces between n-butanol and ethanol. Students measure and plot the boiling temperature of ethanol, n-butanol, and an equimolar mixture. They also compare the behavior of each compound and the mixture as they pass through a gas chromatograph. The goal is to try to understand how the intermolecular forces between the compounds affect their properties. They also attempt to understand the differences in the shapes of the chromatograms as the individual compounds and mixture pass through the column in the gas chromatograph. For these activities the students used a Vernier Mini GC Plus Gas Chromatograph, temperature probes, and Logger Pro® 3 software on a computer.
Open-Source Low-Cost Wireless Potentiometric Instrument for pH Determination Experiments
Hao Jin, Yiheng Qin, Si Pan, Arif U. Alam, Shurong Dong, Raja Ghosh, and M. Jamal Deen; J. Chem. Educ., 2018, 95 (2), 326–330.
The authors describe how to build a low cost pH probe from readily available, off-the-shelf parts. Their system uses an Arduino® board to process the data from a glass pH electrode. They also incorporate a temperature sensor and Bluetooth® wireless technology. They program their system using the Arduino Sketch programing language. The authors hope that by building this system their students will better understand how a pH meter works. A Go!Link and Voltage Probe were used to measure the voltage produced by the glass pH electrode.
Quantifying Sucralose in a Water-Treatment Wetlands: Service-Learning in the Analytical Chemistry Laboratory
Emily C. Heider, Domenic Valenti, Ruth L. Long, Amel Garbou, Matthew Rex, and James K. Harper; J. Chem. Educ., Articles ASAP (As Soon As Publishable).
As part of a service learning approach to increasing community engagement, students perform analytical chemical tests of wetlands to determine pH, chloride, total dissolved solids, and phosphorus. Since Sucralose has been determined to be a indicator of anthropogenic waste in natural waters, students also test for this artificial sweetener. A Conductivity Probe was used to determine total dissolved solids. Students measure the conductivity of the samples in µS/cm and then converted this value to ppm.