Dealing with Dust Entrained in the Nitrogen Plume Demonstration.

Water condensation plumes produced by the addition of iron powder to liquid nitrogen can be contaminated with small quantities of particulate matter. Variations on the plume demonstration, including those using noisemakers, are described to help minimize the release of particulates into the air.

Plumes from Using Iron to Boil Liquid Nitrogen to Illustrate the Importance of Surface Area.

The relationship between surface area and dynamics of processes can be demonstrated by adding iron at room temperature to liquid nitrogen. The rate at which the liquid nitrogen boils to produce gas is related to the surface area of the iron. Adding iron in the form of consistent units that have measurable sizes can be readily connected to observable differences in rates of nitrogen gas production. For example, samples of smaller iron spheres with their greater surface area transfer heat more quickly than do larger spheres of the same volume to liquid nitrogen causing it to boil faster, but more briefly, and produce larger plumes of nitrogen gas from a container vent. The plumes are essentially comprised of nitrogen and water, which make them potentially safer than plumes from other demonstrations such as the "genie in a bottle", based on hydrogen peroxide decomposition. These simple activities can be used as stand-alone demonstrations or as the basis of laboratory activities.

Ethanol as a Probe for the Mechanism of Bubble Nucleation in the Diet Coke and Mentos Experiment.

The Diet Coke and Mentos experiment involves dropping Mentos candies into carbonated beverages to produce a fountain. This simple experiment has enjoyed popularity with science teachers and the general public. Studies of the physicochemical processes involved in the generation of the fountain have been largely informed by the physics of bubble nucleation. Herein, we probe the effect of ethanol addition on the Diet Coke and Mentos experiment to explore the impact that beverage surface tension and viscosity have on the heights of fountains achieved. Our results indicate that current descriptions of the effects of surface tension and viscosity are not completely understood. We also extend and apply a previously reported, simplified version of Brunauer-Emmett-Teller theory to investigate kinetic and mechanistic aspects of bubble nucleation on the surface of Mentos candies in carbonated beverages. A combination of this new theory and experiment allows for the estimation that the nucleation sites on the Mentos candy that catalyze degassing are 1-3 µm in size, and that between 50,000 and 300,000 of these sites actively nucleate bubbles on a single Mentos candy. While the methods employed are not highly sophisticated, they have potential to stimulate fresh investigations and insights into bubble nucleation in carbonated beverages.

Fluoride inhibition of photosystem II and the effect of removal of the PsbQ subunit.

Photosystem II (PSII), the light-absorbing complex of photosynthesis that evolves oxygen, requires chloride for activation of the oxygen evolving complex (OEC). In this study, fluoride was characterized as an inhibitor of Cl(-)-activated oxygen evolution in higher plant PSII. It was confirmed to be primarily a competitive inhibitor in intact PSII, with Cl(-)-competitive inhibition constant K(i) = 2 mM and uncompetitive inhibition constant K'(1) = 79 mM. A pH dependence study showed that fluoride inhibition was more pronounced at lower pH values. In order to determine the location of the fluoride effect, PSII preparations lacking various amounts of the PsbQ subunit were prepared. The competitive F(-) inhibition constant and the Michaelis constant for Cl(-) activation increased with loss of the PsbQ subunit, while the uncompetitive F(-) inhibition constant was relatively insensitive to loss of PsbQ. The S(2) state EPR signals from PSII lacking PsbQ responded to Ca(2+) and Cl(-) removal and to F(-) treatment similar to intact PSII, with enhancement of the g = 4.1 signal and suppression of the multiline signal, but the effects were more pronounced in PSII lacking PsbQ. Together, these results support the interpretation that the PsbQ subunit has a role in retaining anions within the OEC.