Proposed Demonstrations for Lecture

The demonstrations for this lecture focus on H-bonding and polarity. One demonstration addresses chirality. 

In this spectacular demonstration, a light projected from a stroboscope is used to observe that water droplets coming from a separatory funnel are spherical, and that the direction of the stream of these droplets can be deflected by static electricity. 

The demonstration involves an aqueous solution of fluorescein placed in a separatory funnel, under which a large beaker is placed on the floor. Then, the lights in the lecture hall are turned off, the stopcock of the funnel is opened just slightly to produce droplets, and the stroboscope light is turned on. As the green-glowing droplets fall, their shape is carefully examined they are spherical. 

Why are droplets spherical and not shaped differently The water molecules are held by hydrogen bonds (H-bonds), and they prefer to surround themselves by other water molecules, so as to maximize the H-bonding interactions. Thus, a water molecule always prefers to be at the center of the drop rather than at the surface, where it will lack at least one H-bond (tins phenomenon is also known as surface tension). Recalling geometry classes, the shape that has the smallest surface enclosing a given volume is a sphere. And this is the physical shape the droplets adopt, so as to minimize the loss of H-bonding. 

The polarity of water molecules is demonstrated in the second part of the experiment by bending the stream of water droplets using static electricity. To do so, a 

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A.3 Proposed Demonstrations for Lecture 9 Colorful complexes of nickel... 

Many lecture experiments have been proposed for demonstrating the laws of chemical kinetics. Nevertheless, they fail to meet those criteria one can justifiably impose for lecture-demonstration purposes from the standpoint of simplicity, transparency, impressiveness, and reliability. With respect to impressiveness and clarity of the phenomenon, as well as the element of surprise, the Landolt experiment stands out in first place. Conducted in the usual way, however, it is necessarily deprived of its simplicity and transparency. 

I am aware of the difficulties of performing demonstrations (demos) in class due to strict safety measures. Nevertheless, demos should be an essential part of most courses in chemistry, certainly in introductory courses. Let me state the goals of the proposed demos for this opening lecture. 

A thermodynamic course in which the chemical potential was introduced in the manner described was first proposed in 1972 by G. Job [1—4], Since then, the approach has been successfully applied in introductory lectures in thermodynamics at the Universities of Hamburg and Karlsruhe, Germany. It was also adopted in H.U. Fuchs textbook The Dynamics of Heat [5]. Because of the elementary intuitive interpretation of the quantity the concept can be easily adapted to all levels of education. It is already a part of textbooks for schools in Germany [6] and Switzerland [7]. It also plays an important role in the textbook Physical Chemistry - An Introduction with New Concept and Numerous Experiments [8] for undergraduates now in preparation. For strengthening of the understanding theory is complemented by more than a hundred illustrative, simple and safe demonstration experiments. 

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