by Balakrishnan Viswanathan and Mohamed Shajahan Gulam Razul
Original Research
Combustion analysis is typically taught within the context of molecular stoichiometry, in particular the study of empirical formula. This approach is rich in the history of chemistry and also relevant to current laboratory practice. However, the complexity inherent in the traditional approach is not suitable for beginning learners; what should be a rich context for exploring chemical connections has in effect been reduced to an algorithm to be memorized. It is proposed that combustion analysis be taught within the context of limiting reagents, as this represents an ideal situation (one reactant in limited quantity and the other in infinite quantity). Moving the pedagogical position of this topic from molecular stoichiometry to reaction stoichiometry reduces the complexity of the problem from four steps to two. More importantly, the proposed method makes it possible to harness the knowledge that students have acquired earlier in the course to solve a problem in a new context. In the new approach, students match coefficients (computed on the reactant side with unknown on the product side) to obtain the composition of the substance being combusted. It is expected that the connection to prior knowledge and acquired skills will help students achieve improved success when solving problems of this nature.
World Journal of Chemical Education. 2020, 8(2), 100-103. DOI: 10.12691/wjce-8-2-6
Pub. Date: May 20, 2020
3303 Views586 Downloads
by Marcel Emmert, Konrad Heß, Patrick Gräb and Ekkehard Geidel
Original Research
It is a challenge in chemical education to understand basic principles of chemical reaction kinetics on an experimental basis because of the relatively extensive experimental setup and the often time-consuming measurement series. This contribution offers an introduction into the field of the temperature dependence of reaction rate with easy-to-use experiments. Data logging systems have been used to get sufficient data-sets to evaluate different measurements in reaction kinetics. Several experiments were designed for practical courses in chemistry, which allow students to derive the simple van‘t Hoff rule on the one hand. On the other hand, the Arrhenius equation can only be derived on the basis of experimental data with the help of information from collision theory and Maxwell-Boltzmann distribution.
World Journal of Chemical Education. 2020, 8(2), 92-99. DOI: 10.12691/wjce-8-2-5
Pub. Date: April 25, 2020
6514 Views1074 Downloads
by Muna Bufaroosha, Shaikha S. Al Neyadi, Ahmed Alzamly, Mohamad Toutounji, Na’il Saleh, Bashar Yousef Abuhattab, Abdullah Al-Hemyari, Amna Alyammahi, Shamma Alzahmi, Mohamed Altubji and Ruba Al-Ajeil
Original Research
In this work, an undergraduate-level experiment using 5,10,15,20-tetraphenylporphyrin (H2TPP) and its corresponding Ni(II) and Zn(II) metal complexes was developed. The bandgaps of H2TPP and its Ni(II) and Zn(II) metal complexes were calculated experimentally and theoretically to evaluate their abilities to act as light-harvesting complexes.
World Journal of Chemical Education. 2020, 8(2), 87-91. DOI: 10.12691/wjce-8-2-4
Pub. Date: April 22, 2020
4696 Views610 Downloads
by Achim Habekost
Original Research
Spectroelectrochemistry of Electrochromic and electroluminescent substances shows a strong correlation between electrochemical reactions on electrodes and changes in absorbance or luminescence adjacent to the electrode. This was demonstrated by the well-known substances methylviologen and tris (2,2’-bipyridyl) dichloro-ruthenium [Ru (bpy)3]2+. The experimental setup used a conventional potent iostat connected to a fiber spectrometer. Different commercial spectroelectrochemical cells were used: A thin-film absorption cell with a platinum mesh working electrode and as pecular reflection/transmission cell with different screen-printed electrodes. For luminescence measurements, a conventional quartz cuvette with the platinum mesh electrode was used. All cells were inserted into commercial cell holders with connectors for optical fibers. Spectroelectrochemistry becomes increasingly important as an analytical method. In addition, the empirically observed didactical problems of misunderstanding electrochemical electrode reactions can be overcome by visualizing the electrode processes in spectroelectrochemical measurements. The procedures followed in these experiments were designed for typical undergraduate students in electrochemistry.
World Journal of Chemical Education. 2020, 8(2), 71-86. DOI: 10.12691/wjce-8-2-3
Pub. Date: April 01, 2020
8109 Views868 Downloads
by Balakrishnan Viswanathan and Mohamed Shajahan Gulam Razul
Original Research
The standard first-year program includes a section on the balancing of chemical reactions. Students find it difficult to understand this concept as it is increasingly presented as an algorithm or mathematical procedure. This submission outlines a method of teaching students how to balance redox reactions using known chemical principles: oxidation state (including the ionic approximation of molecules), conservation of number (conservation of mass and non-transmutability of chemical particles), and spectator ions. The method involves identification of the oxidation/reduction pairs and balancing the skeletal oxidation/reduction reactions (electron loss/gain) to enforce the link between change in oxidation state and transfer of electrons. The molecular species in the reaction are then built up by adding in other elements with their associated oxidation states, treating them as spectator ions. Equalising the number of electrons in the oxidation and reduction reactions leads to the balanced redox reaction. This method has been tested on a variety of reactions and examples of the three classes of redox reactions are presented. It is expected that students will be able to master the title concept due to the link to fundamental chemical concepts, further enhancing their understanding of the concepts involved.
World Journal of Chemical Education. 2020, 8(2), 67-70. DOI: 10.12691/wjce-8-2-2
Pub. Date: March 24, 2020
4217 Views942 Downloads
by R. Sanjeev and V. Jagannadham
Original Research
The strong empirical relation, ρ = (2.4)(2-i), between the Hammett ρ for proton dissociation of several acids and the number, “i”, of atoms between the ionizable hydrogen and the ring carbon (Andrew Williams, Free Energy Relationships in Organic and Bioorganic Chemistry, Royal Society of Chemistry, Cambridge, 2003, p. 75) is used to construct a graph for twenty one different proton dissociation equilibriums. The plot of Hammett ρ versus number of atoms i between ionizable hydrogen and the ring carbon atom is observed to be an excellent exponential-decay locus. A good average and intelligent value of Hammett ρ is obtained for the benzene dissociation equilibriums by interpolating the locus of the correlation on to Y-axis. Using this Hammett ρ value and the Hammett equation log [(Ka)X / (Ka)H] = ρσ, the pKa value can be calculated for any substituted benzene knowing the pKa value of benzene to be 43. The points for proton dissociation equilibriums of phenylethyl ammonium ions and benzyl alcohols deviated from the graph hence not included in the correlation. Possible explanations are given for deviation of these two equilibriums.
World Journal of Chemical Education. 2020, 8(2), 61-66. DOI: 10.12691/wjce-8-2-1
Pub. Date: March 07, 2020
5494 Views1249 Downloads