Article

A Colorful Demonstration to Visualize and Inquire into Essential Elements of Chemical Equilibrium

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

One of the topics that chemistry teachers have a great challenge introducing is chemical equilibrium. When being introduced to chemical equilibrium, many students have difficulties in understanding that some reactions do not go to completion, as this contrasts most of their supposed prior experiences in chemistry lessons. Students may also struggle with the existence of dynamic equilibrium in which reactants and products constantly transform into each other in a nonvisible manner. The goal of this general chemistry demonstration is to provide teachers with an effective method to help introduce the difficult idea of chemical equilibrium as well as connect chemical equilibrium to acid–base chemistry more successfully. This demonstration will allow students to develop a better understanding of the dynamic nature of chemical equilibrium and Le Chatelier’s Principle by letting them interpret measured pH values and observe correlated color changes before and after the addition of different reagents that shift the chemical equilibrium.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... For illustration: In the current list of experiments, more closed experiments are like an example of demonstrating a chemical equilibrium with a ionexchange resin. 34 A more open investigation is suggested with only some hints regarding how to start the inquiry into the acid− base behavior of zeolites, 35 or a completely open inquiry on hydrophobic sand is introduced. 36 Additionally, the students got a documentation template in which they were able to make notes on each of the experiments. ...
Article
Teacher education needs to combine training in content knowledge, pedagogical knowledge, and pedagogical content knowledge (PCK). One important part of PCK in science education is knowledge about school science practical work to promote learning by scientific inquiry and about the nature of science. In Germany, practical seminars and lab sessions dealing with “school-type” practical work are mandatory for any preservice chemistry teacher education program. Since practice in handling school-type lab equipment is considered important, courses regularly require attendance in practical sessions. These practical experiences are seen as irreplaceable by digital and video materials when it comes to the development of practical and manual skills. This paper reports on the replacement of a traditional course based in a face-to-face seminar combined with half-day lab sessions for a whole cohort of students. This course was replaced by an individualized, digitally supported, open lab learning experience for prospective secondary school chemistry teachers. The change was implemented due to social distancing rules caused by the COVID-19 pandemic. Elements of the course structure are discussed and related to how students experienced the course.
Article
Full-text available
The determination whether a change occurring in a demonstration experiment is a chemical equilibrium reaction and solving equilibrium problems are some of the most important problems for both teachers and students in chemistry education. This study aims to gradually design the teaching of how to determine whether the change occurring in a demonstration experiment is a chemical equilibrium reaction, and how to calculate the equilibrium constant in chemical equilibrium problems through invention and meaningful learning approaches. For this purpose, a two-stage design that explains each stage in solving problems is proposed. In the design including 7 activities, Activity 1 was designed for the first stage and the other activities for the second stage. Understanding Activity 1 is a prerequisite for other activities. The first stage (activity 1) explains how to decide whether a change that occurs in the demonstration experiment is a chemical equilibrium reaction. For Activity 1, four open-ended demonstration experiments whose aim is to observe the effect of temperature change in the context of the Le Châtelier Principle are designed. Activity 2-7 shows how to solve the problem in each stage in the solution method when calculating the equilibrium constant in a chemical equilibrium problem. For Activity 2-7, eleven problems with solutions are given. All activities can be useful for high school or undergraduate chemistry students while learning the concepts of chemical equilibrium, Equilibrium Theory and Le Châtelier Principle. It can be said that via these activities, students will be able to learn the subject of chemical equilibrium in a meaningful way and calculate the equilibrium constant easily in the context of stoichiometry. Keywords: Chemical equilibrium, Stoichiometry, Le Châtelier Principle, demonstration experiment, equilibrium theory.
Article
Full-text available
In simple, reversible, chemical reactions of the type A ⇋ B, chemical equilibrium is related to chemical kinetics via the equality between the equilibrium constant and the ratio of the forward to the reverse rate-constant, i.e., Keq = kf/kr, where Keq is the equilibrium constant and kf and kr denote the rate constants for the forward (A → B) and reverse (B → A) reactions, respectively. We review and examine the relation between the number of forward and reverse reactions required to take place for the aforementioned system to reach equilibrium and the ratio of the forward to the reverse rate constant. Each cycle of reactants becoming products and the products becoming reactants is defined as the transfer cycle (TC). Therefore, we underscore the relation between the number of TCs required for the system to equilibrate and kf/kr. We also vary the initial concentrations of the reactants and products to examine their dependency of the relation between the number of TCs required to reach equilibrium and kf/kr. The data reveal a logarithmic growth-type relation between the number of TCs required for the system to achieve equilibrium and kf/kr. The results of this relation are discussed in the context of several scenarios that populate the trajectory. We conclude by introducing students and researchers in the area of chemistry and biochemistry to physical phenomena that relate the initial concentrations of the reactants and products and kf/kr to the number of TCs necessary for the system to equilibrate.
Article
Acid−base chemistry tends to be one of the more challenging concepts for students to master in high school and undergraduate chemistry curriculum. Mastery of acid−base chemistry requires a concrete understanding of acid−base theories, chemical equilibrium, electronegativity, periodic trends, and the ability to conceptualize intricate processes at a molecular level. Because of the complex nature of the topic, a combination of effective teaching methods should be used. This paper presents an intriguing acid−base demonstration coupled with a detective story that was designed to aid instructors in engaging students while promoting a conceptual understanding of acids and bases. The selected compounds, X and Y, bring additional value and mystery to the demonstration. X and Y are types of faujasite zeolites, three-dimensional crystalline compounds with various useful chemical properties. Although zeolites are used widely in technology and in everyday products such as laundry detergents, their use in the general chemistry curriculum is surprisingly low. This demonstration provides instructors with the opportunity to cover this important group of compounds and elaborate on the behavior of solid state acids and bases at the same time. As a bonus, this demonstration can also be used to revisit Le Châtelier’s principle of chemical equilibrium in a novel context.
Article
The chief physical chemical considerations that govern ion-exchange reactions are that: 1) ions tend to concentrate in the resin phase, and 2) exchanges between ions are equilibrium processes, with equilibrium constants that do not differ greatly from unity. Keywords (Audience): Upper-Division UndergraduateKeywords (Domain): Physical ChemistryKeywords (Feature): Report of the New England Association of Chemistry TeachersKeywords (Subject): Ion Exchange
Article
Zeolites and zeolite-like materials are continually finding new applications. Because of the uniformity of these solids, the expression of macroscale materials properties that are controlled by the materials chemistry at the atomic/molecular scale are achievable. In this Perspective, I discuss the following areas of current interest in zeolites and zeolite-like materials that rely on manipulation of the materials chemistry for their preparation and provide new opportunities for application: (i) exploitation of organic structure-directing agents (SDAs) for new materials, (ii) the synthesis of zeolites without SDAs, (iii) the synthesis of very hydrophobic materials, (iv) conversions of two-dimensional (2D) to 3D materials and vice versa, (v) hierarchically organized materials, (vi) chiral materials, and (vii) direction of tetrahedral atoms to specific framework positions.
Article
A novel didactic sequence is proposed for the teaching of chemical equilibrium. This teaching sequence takes into account the historical and epistemological evolution of the concept, the alternative conceptions and learning difficulties highlighted by teaching science and research in education, and the need to focus on both the students’ learning process and the knowledge to learn.
Article
A hands-on laboratory exercise at the general chemistry level introduces students to chemical equilibrium through a simulation that uses poker chips and rate equations. More specifically, the exercise allows students to explore reaction tables, dynamic chemical equilibrium, equilibrium constant expressions, and the equilibrium constant based on rate constants. Poker chips are used to simulate the reactants and products of two reversible elementary reactions. © 2012 The American Chemical Society and Division of Chemical Education, Inc.
Article
The historical uses of ion-exchange resins and a summary of the basic chemical principles involved in the ion-exchange process are discussed. Specific applications of ion-exchange resins are provided. The utility of these agents to stabilize drugs are evaluated. Commonly occurring chemical and physical incompatibilities are reviewed. Ion-exchange resins have found applicability as inactive pharmaceutical constituents, particularly as disintegrants (inactive tablet ingredient whose function is to rapidly disrupt the tablet matrix on contact with gastric fluid). One of the more elegant approaches to improving palatability of ionizable drugs is the use of ion-exchange resins as taste-masking agents. The selection, optimization of drug:resin ratio and particle size, together with a review of scaleup of typical manufacturing processes for taste-masked products are provided. Ion-exchange resins have been extensively utilized in oral sustained-release products. The selection, optimization of drug:resin ratio and particle size, together with a summary of commonly occurring commercial sustained-release products are discussed. Ion-exchange resins have also been used in topical products for local application to the skin, including those where drug flux is controlled by a differential electrical current (ionotophoretic delivery). General applicability of ion-exchange resins, including ophthalmic delivery, nasal delivery, use as drugs in their own right (e.g., colestyramine, formerly referred to as cholestyramine), as well as measuring gastrointestinal transit times, are discussed. Finally, pharmaceutical monographs for ion-exchange resins are reviewed. Keywords (Audience): Second-Year Undergraduate
Article
The conceptual difficulties of undergraduate students in some aspects of chemical equilibrium and thermodynamics are discussed along with teaching strategies for dealing with these difficulties. Keywords (Audience): High School / Introductory Chemistry
Article
Four analogies are described for use in introductory chemistry classes. Keywords (Audience): High School / Introductory Chemistry
Article
An equilibrium machine powered by air pressure that demonstrates the concepts of equilibrium, activation energy, and catalysis. Keywords (Audience): High School / Introductory Chemistry
Article
In this article a cognitive model of learning chemistry is reported first, followed by a discussion of students' chemical misconceptions, and finally the implications of these findings on instruction. Keywords (Audience): High School / Introductory Chemistry
Article
Chemistry teachers have assumed implicitly that being able to solve problems is equivalent to understanding molecular concepts; this study examines whether this widespread assumption is justified. Keywords (Audience): High School / Introductory Chemistry
Article
The learning of chemistry is described as a process analogous to the process of making chemical discoveries. Historical examples are given to show how chemists have used their insight to break out of a conceptual loop in order to advance the science. Having the insight to make the intuitive leap necessary to break a conceptual loop is as important as having the mastery of the pertinent facts. As in making chemical discoveries, learning elementary chemistry requires developing insight as well as acquiring mastery of the facts. However, current general chemistry teaching tends to teach facts first and insight later. Suggestions for improving this situation so that insight and facts are learned together are given. Finally, the nature of insight is probed more deeply and presented as a two-step process where the first step is an evaluation of the perceptions about science which are held. Once the student, teacher, or researcher has a clear evaluation of the validity of the perceptions that he or she holds, further significant progress toward understanding or scientific discovery is possible.
Products of chemistry pharmaceutical applications of ion-exchange Resins
  • D J Sawyer
  • T E Martens
  • A S Travels
  • C Dancina
  • G Ravner-Canham
  • F Rogers
  • P Huddle
  • M W White
  • M B Nakhleh
  • D P Elder
  • H Beall
  • J Trimbur
  • S J Weininger
  • Mastery
Sawyer, D. J.; Martens, T. E. An equilibrium machine. J. Chem. Educ. 1992, 69, 551. (6) Travels, A. S.; Dancina, C.; Ravner-Canham, G. Applications and analogies. J. Chem. Educ. 1994, 71, 943−944. (7) Rogers, F.; Huddle, P. a.; White, M. W. Simulations for teaching chemical equilibrium. J. Chem. Educ. 2000, 77, 920. (8) Nakhleh, M. B. Why some students don't learn chemistry: Chemical misconceptions. J. Chem. Educ. 1992, 69, 191. (9) Elder, D. P. Products of chemistry pharmaceutical applications of ion-exchange Resins. J. Chem. Educ. 2005, 82, 575−587. (10) Davis, M. E. Zeolites from a materials chemistry perspective. Chem. Mater. 2014, 26, 239−245. (11) Winter, S. S. Ion-exchange separations. J. Chem. Educ. 1956, 33, 473. (12) Beall, H.; Trimbur, J.; Weininger, S. J. Mastery, insight, and the teaching of chemistry. J. Sci. Educ. Technol. 1994, 3, 99−105.
Ravner-Canham, G. Applications and analogies
  • A S Travels
  • C Dancina
Travels, A. S.; Dancina, C.; Ravner-Canham, G. Applications and analogies. J. Chem. Educ. 1994, 71, 943−944.