The first man-made chemical element was that with atomic number 43. It was produced at the University of California - Berkeley (by neutron bombardment of a molybdenum plate and was chemically identified at the University of Palermo (Italy) in 1937 by Segrè and Perrier. Previous attempts to identify it in natural ore had been unsuccessful, owing to the short life of its isotopes. Notwithstanding, several claims of its discovery had appeared in the chemical literature. The history of this discovery clearly shows the dramatic improvements of chemical analytical techniques and criteria in the first half of 20th century. In 1949 its discoverers proposed to call it technetium, which means produced by technology
Student understanding of the laws that describe the flow of a fluid is often hampered by a defective knowledge of basic classical mechanics (kinematics, statics, dynamics, and conservation laws) and by wrong common-sense ideas about quantities related to fluids, such as velocity and pressure. A pedagogical discussion about the Venturi effect, based on experiments inspired by historical instruments, may be an effective way to introduce students to these laws. In this paper, we discuss an approach to the understanding of the Venturi effect based on the study of historical instruments and on simple experiments. In particular, after a presentation of the Venturi effect, also from a historical point of view, we illustrate some interesting applications, the Venturi meter, the Bunsen burner, the Venturi vacuum pump, and propose some simple experiments.
The complex formation between the uranyl (UO2
2+) ion and the diethylene triaminopentaacetate ligand (DTPA) has been investigated at 25 °C, in a 3 M sodium perchlorate medium. The overall protonation constants β
j
H of the free ligand have been previously determined in this ionic medium: six protonated species (H
j
A), with j ranging from 1 to 6, together with the free anion A5− have been identified in the concentration range from (3·10−3 to 13·10−3) mol·kg−1. Four complex species, H2UO2A−, HUO2A2−, UO2A3−, and UO2AOH4−, have been identified in the total uranyl concentration range from (1.1·10−3 to 5.7·10−3) mol·kg−1, and their overall stability constants determined, keeping the metal to ligand ratio equal to 1. Owing to the complex species formation, uranyl ions could be kept in solution until −log h = 7.
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