All Titration Indicators are Not Created Equal—A Lecture Demonstration

This demonstration provides a simple method for emphasizing the importance of indicator selection to determine the end point of a titration involving the common weak base household ammonia. By using phenolphthalein and methyl red as the indicators in the titration of two samples of aqueous household ammonia with hydrochloric acid, students can discover that there is a difference between the two apparent termination points. There is clearly a visible difference in the sharpness of the color changes that take place, and the presence of ammonia at the apparent phenolphthalein endpoint is also detected by olfactory means. By showing the different termination ranges on a titration curve, the students can readily see that phenolphthalein does a poor job of showing the proper termination point,; whereas methyl red shows the proper titration end point.     

FTIR studies of intermolecular hydrogen bonding in halogenated ethanols

The effect of halogen substitution on intermolecular hydrogen-bonding in ethanol is studied. Specifically, Fourier-transform infrared (FTIR) spectra of ethanol, 2,2,2-trifluoroethanol (TFE), and 2,2,2-trichloroethanol dissolved in carbon tetrachloride are reported as a function of temperature and concentration. The spectral intensities corresponding to monomer, dimer, and multimer formation are used to determine the effect of halogen substitution on intermolecular hydrogen-bonding. The enthalpy for dimerization was found to evolve from -4.2+/-0.3 kcal/mol in ethanol to -6.8+/-1.0 kcal/mol in TFE. An opposite trend was observed for multimer formation with enthalpies of -3.7+/-0.5 in ethanol and -2.1+/-1.4 kcal/mol in TFE. The majority of this evolution is assigned to the ability of ethanols to form intramolecular hydrogen bonds involving the hydoxyl proton and the halogen substituents.     

Cyclic voltammetric studies of a thionine coated pyrolytic graphite electrode

Cyclic voltammetry has been used to study the spontaneous adsorption and oxidative coating of thionine onto basal plane pyrolytic graphite electodes. Spontaneous adsorption leads to a monolayer of flat lying molecules together with some weakly attached upper layers. Oxidation of an adsorbed thionine monolayer results in several products which appear to include polymeric species and the sulphoxide of thionine. Similar products are obtained by an oxidative coating procedure.     

Nuclear magnetic resonance spectroscopy of rat ventricles following chronic hypoxia: A model of right ventricular hypertrophy

Nuclear magnetic resonance spectroscopy was used to study the effect of chronic hypoxia on both right (RV) and left ventricular and septal (LV + S) muscle. Rats in the hypoxic group, kept in a hypobaric chamber at $\text{1}\text{2}$ atm pressure for 2 weeks, developed right, but not left, ventricular hypertrophy (p < 0.001). Tissues were studied within 2.5 h of return to air. T₁ and T₂ relaxation times of RV, LV + S and thigh muscle (Th) from hypoxic and control rats were compared. The T₂ value distinguished hypoxic from control RV (p < 0.002), but not hypoxic from control LV + S or Th, indicating that the change in relaxation time reflects cellular hypertrophy, and not hypoxemia. For hypoxic rats only the T₂ value distinguished each muscle type: RV from LV + S (p < 0.009), RV from Th (p < 0.001) and LV + S from Th (p < 0001). The T₁ value did not identify either the hypoxic or control group or the type of muscle. Percent water content was similar for all tissues. For hypoxic RV, T₂ correlated with the percent water content (r = 0.89; p < 0.01). The sensitivity of T₂ to the cellular changes associated with hypoxic RV hypertrophy could provide a means of detecting right ventricular hypertrophy.     

Modeling of high-pressure 12-μm NH3 lasers

Experimental measurements of small-signal gain in an optically-pumped NH₃ amplifier are carried out at pressures ranging from 40 Torr to 760 Torr, and the results are used to validate a rate-equation model describing the amplifier dynamics. The gain measurements show that dilute mixtures of <0.5% NH₃ in N₂ are reqired to minimize the problems of gas heating due to pump absorption. The model is used to extrapolate the results to gas pressures of several atmospheres, and to demonstrate the potential for highpressure operation of optically-pumped NH₃ lasers. For a pump intensity of 100 MW/cm², calculations indicate that operation of an NH₃–N₂ laser is feasible up to a pressure of 10 atm, which would provide a maximum continuous tuning range of 4 cm^–1. High-resolution spectroscopy reveals that gain on a few NH₃ transitions is eliminated at high pressures due to the presence of overlapping absorptions in other NH₃ bands.     

Missing fractions in heavy gases: Xe and CCl4?

The spin polarization of positive muons thermalized in Xe has been measured as a function of pressure up to 4660 Torr (6.1 atm) by the muon spin rotation (MSR) technique. At 4660 Torr, triplet muonium (F=1, M=1) accounts for about 40% of the initial muon polarization and no significant signal from diamagnetic muons has been observed. The unexpectedly slow recovery of the polarization in Xe at high pressures is discussed in conjunction with similar results seen in CCl₄ and CHCl₃ vapors.     

Realization of digraphs by preferences based on distances in graphs

Consider a graph G with two distinguished sets of vertices: the voters and the candidates. A voter v prefers candidate x to candidate y if d(v, x) < d(v, y). This preference relation defines an asymmetric digraph whose vertices are the candidates, in which there is an arc from candidate x to candidate y if and only if more voters prefer x to y than prefer y to x. T. W. Johnson and P. J. Slater (“Realization of Majority Preference Digraphs by Graphically Determined Voting Patterns,” Congressus Numerantium, vol. 67 [1988] 175-186) have shown that each asymmetric digraph of order n can be realized in this way using a graph of order O(n²). We present a new construction reducing the quadratic upper bound to a linear bound. © 1995 John Wiley & Sons, Inc.     

Mössbauer spectroscopy,electron microscopy and electron diffraction studies of small particle magnetic systems: Identification of disease specific haemosiderins

Mössbauer spectroscopy has shown that the iron-containing cores of the biological iron storage material haemosiderin produced under normal and various pathological conditions are significantly different in their magnetic properties. The differences have been correlated with information on the particle size, morphology, crystallinity and mineral form of the haemosiderin cores obtained by complementary electron microscopy and electron diffraction studies. These results have important implications for the use of Mössbauer spectroscopy in determining the properties of small particle magnetic systems and also considerable relevance for the improved understanding and treatment of iron overload disease.