International Journal of Physics
ISSN (Print): 2333-4568 ISSN (Online): 2333-4576 Website: https://www.sciepub.com/journal/ijp Editor-in-chief: B.D. Indu
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International Journal of Physics. 2024, 12(5), 238-246
DOI: 10.12691/ijp-12-5-7
Open AccessArticle

Understanding Diffusion and Demonstrating it Correctly – A Critical Look at a Transport Process often Incorrectly Taught in Schools

Philipp Meyer1,

1Chemistry Education, University of Potsdam, Potsdam, Germany

Pub. Date: October 27, 2024

Cite this paper:
Philipp Meyer. Understanding Diffusion and Demonstrating it Correctly – A Critical Look at a Transport Process often Incorrectly Taught in Schools. International Journal of Physics. 2024; 12(5):238-246. doi: 10.12691/ijp-12-5-7

Abstract

Diffusion is a transport process frequently shown experimentally in beginning science classes. However, quite a few standard school “diffusion experiments” such as letting food colorant drip into water and spraying perfume (or similar) into a classroom provide a false picture of diffusion by demonstrating convection, transport by flow, instead. The article explains why these two standard experiments clearly show convection and should therefore be banned from school lessons as "diffusion experiments": Diffusion is explained to be an entropy-driven process and, based on this, the so-called Einstein-Smoluchowski equation is derived with the help of simple probability calculations. Using the Einstein-Smoluchowski equation, it is then shown how transport phenomena can be clearly recognized as diffusion or be unmasked as convection experiments. The reader is provided with alternative genuine diffusion experiments for beginning classes that verifiably demonstrate diffusion, namely the spread of ammonia and hydrogen chloride in a sealed glass tube and the spread of methylene blue in water-based gels. Additionally, it is shown how these experiments can be used to quantify diffusion constants with the aid of the Einstein-Smoluchowski equation.

Keywords:
diffusion misconceptions convection school experiments laboratory computing

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References:

[1]  Gründer, S; Schlüter, K.-D., Physiologie hoch2 [engl. Physiology to the power of 2], Elsevier GmbH, München, 2019, 32.
 
[2]  Compton, R.G.; Banks, C.E., Understanding Voltammetry, Imperial College Press, 2010.
 
[3]  Lüders, K.; v. Oppen, G., Bergmann · Schaefer. Lehrbuch der Experimentalphysik, Band 1: Mechanik · Akustik · Wärme [engl. Bergmann · Schaefer. Textbook of Experimental Physics, Volume 1: Mechanics - Acoustics Heat], de Gruyter, Berlin/ New York, 2008, 463-474.
 
[4]  Vogel, S., “Dealing Honestly with Diffusion”, The American Biology Teacher, 1994, 56 (7), 405-407.
 
[5]  Davis, L. C., “”, J. Chem. Educ., 1996, 73 (8), 824-825.
 
[6]  Meyer, P., „Düngung und die Diffusion von Ammoniak“ [engl. Fertilization and the diffusion of ammonia], Chem. Unserer Zeit, 2023, 57 (4), 248-253.
 
[7]  Meyer, P., „Quantitative determination of the diffusion constant of hydrogen chloride in air – A way to eliminate a (school-based) misconception and to re-evaluate the counter-diffusion of HCl and NH3”, J. Chem. Educ., 2023, 100 (12), 4941–4945.
 
[8]  Atkins, P.W., J. de Paula, J., Physikalische Chemie [engl. Physical Chemistry], Wiley-VCH, Weinheim, 2013.
 
[9]  Wedler, G.; Freund, H.-J., Lehrbuch der physikalischen Chemie [engl. textbook of physical chemistry]; Wiley-VCH, Weiheim, 2012.
 
[10]  Hägele, P.C., „Was hat die Entropie mit Information zu tun?“ [engl. What does entropy have to do with information?], manuscript (University of Ulm), Ulm, URL: https://www.uni-ulm.de/~phaegele/Vorlesung/Grundlagen_II/_information.pdf, accessed April 2024.
 
[11]  Kreiner, W.A., „Entropie - was ist das?“ [engl. Entropy - what is that?] Universitätsverlag Ulm GmbH, Ulm/Donau, 2000, 10-15.
 
[12]  Kubb, C., „Diffusion“, biologie-schule.de, Köln, URL: https://www.biologie-schule.de/diffusion.php, accessed April 2024.
 
[13]  Mortimer, C.E.; Müller, U., Chemie: das Basiswissen der Chemie[engl. the basics of chemistry], Thieme, Stuttgart, 2010.
 
[14]  Berg, H.C., Random walks in biology, Princeton University Press, Princeton, 1993, 5-12.
 
[15]  Schwartz, M., „Statistical Mechanics, Lecture 2: Diffusion“, lecture notes (University of Oxford), Oxford, 2019, URL: https://scholar.harvard.edu/schwartz/teaching, accessed April 2024.
 
[16]  Kraska, T., “Mathematical Modeling in Secondary Chemistry Education: Chromatography“, WJCE, 2020, 8 (3), 114–121.
 
[17]  Erbrecht, R.; Felsch, M.; König; H.; Kricke, W.; Martin, K.; Pfeil, W.; Winter, R.; Wörstenfeld, W.; Das grosse Tafelwerk interaktiv [engl. The large interactive table], Cornelsen Verlag, 2009, 39.
 
[18]  Nepf, H., „1. Conceptual model of diffusion. Transport Processes in the Environment. Civil and Environmental Engineering“, lecture notes (Massachusetts Institute of Technology): 1.061 / 1.61 Transport processes in the environment, Massachusetts, 2008, URL: https:// ocw.mit.edu/ courses/ 1-061-transport-processes-in-the-environment-fall-2008/ resources/lec_01/, accessed April 2024.
 
[19]  Dimmock, N.A.; Marshall, G.B., “The determination of hydrogen chloride in ambient air with diffusion/denuder tubes“, Analytica Chimica Acta, 1987, 202, 49–59.
 
[20]  Sir, S., Vol 05: Heat & Thermodynamics: Adaptive Problems, Book in Physics for College & High School: with Detailed Solutions, physicsfactor.com, 2021, 13-P70 – 13-P71.
 
[21]  Endow, S.A.; Russell, A.P., “BASICS: Biophysics A Step-by-Step Introduction to Concepts for Students. Lesson Plan: Diffusion“, Lesson plan & experiments designed for high school teachers and students (Duke University Medical Center, The Biophysical Society), Durham (NC), 2015, URL: https:// www.biophysics.org/biophysics-basics#/, accessed April 2024.
 
[22]  Heintze, J./ Bock, P. (ed.), Lehrbuch zur Experimentalphysik Band 2: Kontinuumsmechanik und Thermodynamik [engl. Textbook of Experimental Physics Volume 2: Continuum Mechanics and Thermodynamics], Springer, Berlin/Heidelberg, 2016, 87-92.
 
[23]  Dämmgen, U.; Schaaf, S.; Horvath, B.; Meesenburg, H.; Mohr, K., „Methoden zur Bestimmung von Stoffflüssen und-konzentrationen im ANSWER-Projekt [engl. Methods for the determination of the flow of substances and concentration of substances in the ANSWER project], Landbauforschung Völkenrode, 2005, Sonderheft (engl. special issue) 279, 23-44.
 
[24]  Gardner, J.H, “A simple experiment illustrating diffusion“, J. Chem. Educ., 1940, 17 (10), 494.
 
[25]  Conard, C.R.; Bent, H.E., “Diffusion of potassium permanganate as a lecture demonstration“, J. Chem. Educ., 1969, 46 (11), 758.
 
[26]  Crooks, J.E., “Measurement of diffusion coefficients“, J. Chem. Educ.,1989, 66 (7), 614-615.
 
[27]  Mostinsky, I.L, “Diffusion coefficient”, Thermopedia. A-to-Z Guide to Thermodynamics, Heat & Mass Transfer, and Fluids Engineering, 2011, URL: 10.1615/AtoZ.d.diffusion_coefficient, last accessed April 2024.
 
[28]  Watts, H., “Diffusion in liquids: A class experiment“, J. Chem. Educ., 1962, 39 (9), 477.
 
[29]  Gillespie, D.T.; Seitaridou, E., Simple Brownian diffusion: an introduction to the standard theoretical models, Oxford University Press, Oxford: United Kingdom, 2013, 38-42.
 
[30]  Linder, P.W., Nassimbeni, L. R.; Polson, A.; Rodgers, A. L, “The diffusion coefficient of sucrose in water. A physical chemistry experiment“, J. Chem. Educ. 1976, 53 (5). 330-332.
 
[31]  Ribeiro, A.C.F.; Esteso, M.A.; Lobo, V.M.M.; Valente A.J.M; Simôes, S.M.N.; Sobral, A.J.F.N.; Burrows, H.D., “Diffusion Coefficients of Copper Chloride in Aqueous Solutions at 298.15 K and 310.15 K”, J. Chem. Eng. Data, 2005, 50 (6), 1986-1990.
 
[32]  Tang, L., “Concentration dependence of diffusion and migration of chloride ions“, Cement and Concrete Research, 1999, 29 (9), 1463–1468.
 
[33]  Wlodarczyk, J.K.; Baltes, N.; Friedrich, K.A.; Schumacher, J.O., “Mass transport limitations in concentrated aqueous electrolyte solutions: Theoretical and experimental study of the hydrogen–bromine flow battery electrolyte“, Electrochimica Acta, 2023, 461, 142640-1 - 142640-15.
 
[34]  Ichikawa, T.; Haga, K.; Yamada, K., “Physicochemical Analysis of Chloride Diffusion and Adsorption in Water-saturated Concrete: Theory and Measurement“, Journal of Advanced Concrete Technology, 2023, 21 (4), 218–233.
 
[35]  Kizilyalli, M.; Corish, J.; Metselaar, R., “Definitions of Terms for Diffusion in the Solid State (IUPAC Recommendations 1999)“, Pure Appl. Chem., 1999, 71(7), 1307–1325.