World Journal of Chemical Education

In this article we implement the idea of representing an aqueous solution of acids and/or bases with a matrix from which the pH and equilibrium concentrations of all species in any described solution can be extracted. Given that this matrix can be readily generated using an ad hoc MS Excel sheet, whatever pH calculation is reduced to the problem of selecting a row from the matrix by using as a guide the proton balance equation in the solution. A special scheme is presented allowing the needed proton balance relation to be derived from the specified solution data in all cases. This preserves the fundamental unity of the topic without sacrificing chemical understanding and simplicity. By consequence, the presented calculation technique is eminently suitable to be used in introductory courses as a complement, an extension or a substitute whenever the usual way of dealing with the topic (which, in general, consists in developing a menu of special cases, formulas and/or algebraic procedures) is judged insufficient. A MS Excel file named <matrixGenerator.xlsx>, attached to the present paper as supporting material, allows the matrix representation of any given solution to be developed in a very short time.

World Journal of Chemical Education. 2015, 3(4), 93-110. DOI: 10.12691/wjce-3-4-3
Pub. Date: August 16, 2015

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Experimental Determination of Planck’s constant using Light Emitting Diodes (LEDs) and Photoelectric Effect

by Andrea Checchetti and Alessandro Fantini

Original Research

The aim of this experiment was to utilize the Inquiry Based Science Education, (IBSE) in order to offer the students a better understanding of the light-matter interaction. The inquiry-based teaching addresses the question of how the students make observations, develop hypotheses about phenomena, and devise tests to investigate their hypotheses. Using IBSE they share responsibility within the group for what concerns answering questions, and use a scientific approach to solve problems. 4^th year students of undergraduate degree program of an Italian Arts Lyceum and 5^th year students of undergraduate degree program of an Italian Scientific Lyceum have experimentally determined the value of Planck's constant, h. They have used respectively two methods: a) current-voltage measurements of a series of different colored LEDs; b) a method based upon the comparison of the incident light beams values of potential arrest with different wavelength on a photo emissive surface, using the photoelectric effect through an apparatus built on an optical bench. This work is an essential part of an apprenticeship developed during the “Professione Formatore in Didattica delle Scienze” Master, which takes place at the University of Calabria, with the authors taking part in it as trainees and that will be over in the month of October 2015.

World Journal of Chemical Education. 2015, 3(4), 87-92. DOI: 10.12691/wjce-3-4-2
Pub. Date: August 13, 2015

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Electrochromism of Methylviologen (Paraquat)

by N. Aristov and A. Habekost

Original Research

The herbicide paraquat, N, N’-dimethyl-4,4‘-bipyridiunium dication (N,N’-methyl viologen), is electrochromic. Experiments are described that investigate its redox chemistry (cyclic voltammetry), its optical properties (photometry and UV/Vis spectrophotometry), and its potential as a system for electrical “photoswitching” and as an accumulator for rechargeable devices. This set of teaching laboratory experiments closely reflects true procedures in commercial research and development endeavors, because the same system is probed with several quite different, but complementary, analytical methods.

World Journal of Chemical Education. 2015, 3(4), 82-86. DOI: 10.12691/wjce-3-4-1
Pub. Date: July 30, 2015

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