Interdisciplinary Applications for
General Chemistry Laboratory


Table of Contents    
 
 
   

CURRENT ONLINE TUTORIALS

Biological Applications:   Engineering and Environmental Applications:

 

 

 

 


ADDITIONAL ONLINE TUTORIALS

Biological Applications Tutorials:   Engineering and Environmental Applications:

 

 


Introduction:

In General-Chemistry courses, students are exposed to fundamental concepts that have applications in many fields, from biology to engineering technology to understanding day-to-day observations. Often, students in General Chemistry work hard to master these concepts without learning about the interesting applications until they take more advanced courses later. We have designed a series of WEB-based graphical tutorials to enable students to explore some of these applications of chemical principles. Each tutorial is focused on a specific interdisciplinary application that incorporates key chemical concepts suitable for a General-Chemistry course. The purpose of this exploration is twofold: to stimulate students' interest in the course material, and to challenge students to think about the ramifications of chemistry and apply their knowledge to new situations.

Each tutorial begins with a list of the key chemical and application-oriented concepts to be explored. This list highlights for the students the concepts on which they should focus as they study the tutorial. The body of the tutorial begins by introducing how the topic of the tutorial relates to the students' everyday lives. The tutorial then shows how the topic is dependent on specific chemical concepts and emphasizes that, to understand the application in detail, the students must understand the tutorial's specific chemical concepts. Hence, the tutorials teach the key chemical concepts (and any other necessary ideas) in the context of the application. At the end of each main section in the tutorial are questions that require critical-thinking and problem-solving skills, and that refer back to that specific section. Interspersing the questions throughout the tutorial helps the students clarify their understanding of the application and the underlying chemistry as they progress through the tutorial. These questions may pertain to the chemical concepts presented, the application itself, or both.

These tutorials contain several special features that help students to learn how to use computer technology to enhance their understanding and appreciation of chemistry, and to develop their problem-solving skills by integrating information from a variety of sources. These features include three-dimensional molecular representations, interactive molecular viewing (using a molecular-viewing package such as RASMOL), QuickTime movies, and lists of additional links and references for further reading, to serve as a launching point for interested and highly-motivated students to learn more about these subjects.

Index


Suggested Uses for Tutorials:

At Washington University in St. Louis, tutorials are an essential component of the General-Chemistry laboratory course. For each experiment the students perform in lab, there is an accompanying tutorial. Each tutorial is focused on a specific interdisciplinary application that incorporates the key chemical concepts introduced in the corresponding experiment. For example, in our course, the hemoglobin tutorial accompanies a general-chemistry experiment in which students synthesize inorganic compounds containing metal centers using microscale techniques. The key chemical concepts in the experiment are an introduction to metal complexes (their coordination numbers and different ligand types), ligand-exchange processes, and an introduction to electronic-absorption spectroscopy. The tutorial describes the oxygen transport by hemoglobin in the blood, which is dependent on heme, the metal complex in hemoglobin. The key concepts in the tutorial are an introduction to metal complexes (coordination numbers and ligand types), an introduction to protein structure, and an introduction into relationships between structure and function. Hence, the major concepts in the tutorial complement the major concepts in the experiment.

Each tutorial also contains short-answer or calculational questions. The questions are interspersed throughout the tutorial, which helps the students clarify their understanding of the application and the underlying chemistry as they progress through the tutorial. At Washington University in St. Louis, the solutions to these questions are graded and are worth 20% of the total score for each experiment.

However, these tutorials could be used to augment any General-Chemistry curriculum; they are not limited to use with these particular experiments. Because they promote critical thinking about many of the concepts encountered in any General-Chemistry course, instructors could use these tutorials in a variety of different ways. For instance, they could be assigned as extra-credit assignments to complement a related lesson, or students might complete the tutorials outside of class to prepare for a class discussion about the applications of the course material. Some of the questions from the tutorials could be incorporated as challenging test questions. Students might also use these tutorials to generate ideas for research projects.

Although the tutorials work well if used in sequence, so that students continually recall knowledge from previous lessons and apply it to new situations, each tutorial is also designed to be able to stand on its own. Occasionally, there are references to earlier tutorials or to the experiments in our curriculum, but these can generally be ignored, or the instructor could supply the information.

We would like to hear how others have used our tutorials. If you use these tutorials, please acknowledge Washington University in St. Louis, and send a message to R. Frey at gfrey@wustl.edu.

Index


Blood-Chemistry Tutorials:

This set of four tutorials deals with chemical processes in the blood. These tutorials provide an integrated biological context for a variety of chemical concepts including metal complexes, spectroscopy, polarity, molecular size, diffusion, and equilibrium. The tutorials in this set are

The blood-chemistry tutorials build upon one another to help students develop an understanding of the physiological processes, as well as the chemical processes, that occur in the blood during the body's daily activities. The first three tutorials (Hemoglobin, Ferritin, and Dialysis) describe the daily maintenance required in the blood for normal everyday activities such as eating, sleeping, and studying. The last tutorial (Buffers) integrates the chemical and physiological concepts of all four tutorials to explain how the body copes with the stress of exercise. By studying these tutorials, students begin to see that the body has developed finely tuned chemical processes that work in combination to maintain the metabolic status of the blood during normal activities, and to handle the changes in the blood that exercise produces.

At Washington University in St. Louis, two of these tutorials are completed in the first semester of General Chemistry, and two are completed in the second semester of General Chemistry. The first tutorial, “Hemoglobin and the Heme Group: Metal Complexes in the Blood”, describes the role of a metal complex in transporting oxygen in the blood. Next, “Iron Use and Storage in the Body: Ferritin and Molecular Representations” describes ferritin, the protein in the blood and liver that stores iron and controls the amount of iron available to the body. The first tutorial of the second semester, “Maintaining the Body's Chemistry: Dialysis in the Kidneys”, describes how the kidneys use semipermeable membranes and diffusion across concentration gradients to filter the blood. The final tutorial of the set “Blood, Sweat, and Buffers: pH Regulation During Exercise” describes the acid-base equilibria and the pH buffers in the blood. This last tutorial also ties together the story of chemistry in the blood, which the students have been learning about through the other blood-chemistry tutorials.

Index


Hemoglobin and the Heme Group: Metal Complexes in the Blood for Oxygen Transport

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Authors: Rachel Casiday, Richard Krathen, and Regina Frey

Key Concepts:   Metal complexes; protein structure and conformational changes; spectroscopy.

Blood is part of the body's circulatory system, and thus is continually being pumped through our bodies as long as we are alive. The blood distributes oxygen and nutrients to the many different cells in the body, carries CO2 generated by the cells to the lungs for exhalation, and carries other waste products to the kidneys and liver for processing and elimination. Many finely tuned chemical processes occur in the blood to allow the blood to carry out all of these functions and provide for the needs of the body. One of the most important functions of blood is to carry O2 to all parts of the body via the hemoglobin protein. This oxygen transport is accomplished by the heme group (a component of the hemoglobin protein), which is a metal complex with iron as the central metal atom, that can bind or release molecular oxygen. Heme groups are embedded in the hemoglobin protein, so the tutorial gives a view of hemoglobin and its major structural features. The tutorial also describes gas exchange in the blood (CO2 exchanged for O2 in the lungs, and O2 exchanged for CO2 in the muscles), and how both the hemoglobin protein and the heme group undergo conformational changes upon oxygenation and deoxygenation. In addition to showing a molecular view of the changes that occur when hemoglobin is oxygenated or deoxygenated, the tutorial describes the color changes that occur when blood is oxygenated or deoxygenated, and shows how spectroscopy can be used to determine the oxidation of hemogloin. This tutorial is one of four blood-chemistry tutorials available for General Chemistry from Washington University in St. Louis.

At Washington University in St. Louis, this tutorial accompanies a first-semester experiment in which students learn about metal complexes by synthesizing [Co(NH3)6]Cl3 and Cu(NH3)4SO4•H2O in lab. In laab, the students explore ligand-exchange reactions of the Co complex and analyze the results spectrophotometrically. This tutorial explains coordinate-covalent bonding in metal complexes in more detail, and explores how the body uses metal complexes in the protein hemoglobin to transport and release the oxygen ligand. Hence, the tutorial illustrates a biological application of the course material, and lays a foundation for future exploration of these concepts in general chemistry and biology courses.

Index


Iron Use and Storage in the Body: Ferritin and Molecular Representations

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Authors: Rachel Casiday and Regina Frey

Key Concepts:  Graphical molecular representations; protein structural components; crystal-lattice mineral structure; oxidation states; polarity.

Iron is necessary for oxygen transport in the blood, supplying the body with a reliable source of energy, and for maintaining several other important structures and systems in the body. However, too much free iron in the blood can lead to the dangerous disease known as hemochromatosis. How does the body regulate the amount of iron? Fortunately, most of us are able to maintain appropriate levels of available iron in the body (enough available iron to ensure an adequate supply of hemoglobin, but not so much as to produce toxic effects), even if our iron consumption does not always exactly match the body's iron loss. Ferritin is the key to this important control of the amount of iron available to the body. Ferritin is a hollow, spherical protein that stores iron and releases it in a controlled fashion. Hence, the body has a "buffer" against iron deficiency (if the blood has too little iron, ferritin can release more) and, to a lesser extent, iron overload (if the blood and tissues of the body have too much iron, ferritin can help to store the excess iron). Ferritin stores iron as Fe(III) in a crystal-lattice mineral structure inside the hollow sphere of the protein. Iron is released from the protein as water-soluble Fe(II).

The tutorial uses a variety of molecular representations to describe the structure of ferritin, and how the structural components and features (e.g., polar and nonpolar amino acids, peptides, and channels) allow the protein to store iron and release it in a controlled fashion. Hence, a major segment of the tutorial introduces students to different types of molecular representations, describing the advantages and limitations of each, so that students appreciate that different types of representations give different information about a molecule. The tutorial describes protein structure in detail appropriate for students with little or no background in biology, and applies the information about protein structure to the ferritin protein. A final section describes the mechanism by which iron is released from the protein. This tutorial is one of four blood-chemistry tutorials available for General Chemistry from Washington University in St. Louis.

At Washington University in St. Louis, this tutorial is used in conjunction with a first-semester laboratory experiment in which the students use the spectrophotometer to perform a trace analysis of the iron content in ferritin and to observe the kinetics of the iron-release process. First, the total amount of iron in a ferritin sample is determined by breaking apart the protein shell, and then the time course of iron released from the intact protein by the reduction of the iron-mineral core is determined. In this manner, the mechanism of the in-vitro iron-release process is examined.

An earlier molecular-graphics tutorial on ferritin, designed for second-year students, and detailed information about the ferritin experiment are also available.

Index


Maintaining the Body's Chemistry: Dialysis in the Kidneys

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Authors: Rachel Casiday and Regina Frey

Key Concepts:  Semipermeable mebranes; polarity; diffusion and concentration gradients; dynamic equilibrium.

Blood contains particles of many different sizes and types, including cells, proteins, dissolved ions, and organic waste products. It is the job of the kidneys to remove the harmful particles from the blood and regulate the blood's ionic concentrations, while keeping the essential particles in the blood. The kidneys meet these challenges through a remarkably elegant system. The kidneys use specialized membrane channels and concentration gradients to control the passage of particles between the tubules (specialized components of the kidney that ultimately lead to the ureter for excretion), and the circulating blood. In describing the process by which the kidneys filter blood, the tutorial emphasizes the importance of hydrophilic and hydrophobic properties, concentration gradients and diffusion, and membrane structure. The tutorial then describes artificial dialysis using a cellulose membrane, and shows how the same underlying chemical principles are at work in both natural and artificial kidneys. This tutorial is one of four blood-chemistry tutorials available for General Chemistry from Washington University in St. Louis.

At Washington University in St. Louis, this tutorial accompanies a second-semester experiment in which students learn about biological and artificial membranes, concentration gradients and diffusion across a semipermeable membrane, and the solubility properties of hydrophobic, hydrophilic, and amphipathic molecules. In the experiment, students use a semipermeable cellulose membrane (similar to the membranes used in artificial kidneys) to separate chlorophyll from the proteins to which it is attached in plant cells, study the time-course change in a pH gradient, and examine the effect of detergent on oil-water miscibility.

Index


Improving Air Quality with Electric Vehicles

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Authors: Carolyn Herman and Regina Frey

Key Concept:   Good air quality is a major factor in public health.  Photochemical smog is the most common air-quality problem.  This tutorial describes the harmful components of air pollution, the important sources of air pollution in the United States, and several strategies for reducing air pollution.  Redox reactions are the basis for understanding each of these topics.  For example, one of the major components of air pollution is ozone, and it is the oxidative ability of ozone that causes the harmful effects.  The tutorial discusses the oxidative ability of ozone in the body.

Automotive emissions increase the ozone concentration even though ozone is not directly produced by these emissions.  A simplified mechanism is presented for the production of ozone, and hence the students are introduced to mechanistic chemistry.  Current strategies for reducing emissions are discussed, which lead to a discussion of the development of zero-emissions vehicles (ZEV).  The current ZEV are electric vehicles and their feasibility is dependent on battery technology, where energy is produced by an oxidation-reduction reaction.  The electrochemical cell is the foundation of all batteries.  Most electric vehicles use the lead-acid battery (which is the conventional car battery), but there are a number of drawbacks to this battery, namely the weight and the recharging time.  Hence, battery technology is an active area of research.  This tutorial describes one interesting new design, namely a vanadium-flow battery in which the redox reaction involves solutions instead of solid material.  A current is produced through electron transfer from the vanadium (II) ions in solution on one side of the battery to the vanadium (V) ions on the other side.  This design looks promising, but it is in its infancy.  Thus this tutorial shows that to understand air pollution, its effects, and how to reduce air pollution, one must understand electrochemistry, redox reactions, and the connection between chemical and electrical energy.

At Washington University in St. Louis, this tutorial accompanies a second-semester experiment, "Electrochemistry: Cells and Redox Reactions." In this experiment, students learn how to construct an electrochemical cell and how cell potential depends upon the concentrations of the reacting species in the cell.  The tutorial expands upon these concepts.  Electrochemical methods and redox reactions are discussed from the perspective of air quality, its impact on human health, and the role of battery technologies in addressing air-quality problems. 

This tutorial and the associated electrochemistry experiment nicely complement the "Energy for the Body: Oxidative Phosphorylation" tutorial and its associated experiment "Redox Reactions: Iron Plus Dichromate".

Index


Energy for the Body: Oxidative Phosphorylation

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Authors: Rachel Casiday and Regina Frey

Key Concepts:   Coupled reactions; oxidation-reduction reactions; reduction potential and free energy; concentration gradients.

Every day, we build bones, move muscles, eat food, think, and perform many other activities with our bodies. How do we do all of these activities? All of these activities are based upon chemical reactions. However, most of these reactions are not spontaneous (i.e., they are accompanied by a positive change in free energy, DG>0) and do not occur without some other source of free energy. Hence, the body needs some sort of "free-energy currency," a molecule with one or more bonds that can easily be broken to release free energy when it is needed to power a given biochemical reaction. This tutorial describes two important aspects of the free-energy problem:

  1. how the free-energy currency works to make a nonspontaneous reaction spontaneous. The solution, which is based on thermodynamics, is to use coupled reactions.
  2. how the body produces the major molecule that is used as the free-energy currency. This molecule is synthesized primarily by a two-step process consisting of an electron-transport chain and a proton gradient.  This process is based on electrochemistry and equilibrium, as well as thermodynamics.

The most important free-energy molecule in the body is ATP. ATP is a useful free-energy currency because it can lose a phosphate group in a very spontaneous reaction; i.e., the dephosphorylation reaction releases a large amount of free energy. The dephosphorylation reaction of ATP is often coupled with nonspontaneous reactions to drive them forward. To produce ATP, another set of coupled reactions, known as oxidative phosphorylation, is used. Oxidative phosphorylation consists of two major components: (1) the oxidation of molecules generated during the breakdown of glucose, which releases energy that causes a proton gradient to build up across a membrane, and (2) the phosphorylation of ADP to make ATP, using energy from the proton gradient.

This tutorial explains the importance of ATP in driving nonspontaneous reactions by coupled reactions, and describes in detail the process by which the body makes ATP for use as its free-energy currency. Important components of this description include the structure of mitochondria (organelles in which oxidative phosphorylation occurs), the proteins involved in oxidative phosphorylation, the reactions that occur, and reduction potential. A special section of the tutorial explains the relationship between reduction potential and free-energy change.

At Washington University in St. Louis, this tutorial accompanies a second-semester experiment in which students perform a redox titration with dichromate to quantitate the percent of iron in an iron-oxide sample. The experiment teaches students about oxidation and reduction half-reactions, the importance of potential in determining the oxidizing strength of a species, and the relationship between reduction potentials and equilibrium constants. The tutorial develops this understanding of oxidation-reduction reactions by showing the relationship between potential and free energy, providing a qualitative description of a series of oxidation-reduction reactions, and showing a real-life application of these chemical concepts.

Index


Nutrients and Solubility

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Authors: Rachel Casiday, Richard Krathen, and Regina Frey

Key Concepts:   Molecular basis for solubility; polarity; thermodynamics of dissolution; solubility (quantitative) and solubility product.

In order to use the nutrients that we take in when we eat, we must first break the food down into its nutritive components, dissolve these components, and then carry them to the place where they will be used in the body. If the nutrients are not used immediately, they will either be stored for later use, or excreted in the urine. Understanding the solubility of nutrients in the different substances of the body is important for understanding how they can be used or processed in the body. Scientists have developed several ways to discuss the important concepts of solubility. For salts (ionic solids) that dissociate into ions in water, such as the compounds containing the dietary minerals, a solubility product Ksp is typically given. Vitamins are typically described as soluble in water or in lipids, depending on the functional groups on the molecule. A vitamin's solubility in water or in lipids determines where it can be used, and whether it will be stored in fat cells or excreted from the body if it is not needed for immediate use.

In this tutorial, students learn about the thermodynamics and structural properties of a molecule that make it soluble or insoluble in a given solvent (e.g., water or fat). A table of vitamin structures allows students to examine the two-dimensional (ChemDraw) and three-dimensional (CPK) structures of seven vitamins. Students can also download and view the three-dimensional structures interactively using an interactive molecular-viewing package such as RASMOL. Olestra, the new fake fat in some snack foods, is discussed because it interferes with the body's absorption of fat-soluble vitamins. The solubility of minerals is explained quantitatively, using the concepts of equilibria and the solubility product (Ksp). The role of calcium in the body, equilibria involving blood-calcium concentration, and the solubility of calcium supplements, are discussed in detail.

At Washington University in St. Louis, this tutorial accompanies a second-semester experiment in which students determine the solubility product for Ca(OH)2 and determine the effect of OH- concentration on the solubility of this compound (common-ion effect). The tutorial gives a relevant example (minerals in your body) of where this quantitative solubility product is used.  It also develops the students' understanding of the common phrase "like dissolves like".

Index


What's In A Name: The Nomenclature of Inorganic Compounds

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Author: Kit Mao

Key Concepts: Naming of simple cations, anions, and polyatomic ions; naming of compounds of great ionic characters, compounds of great covalent character, and inorganic acids; nomenclature of coordination compounds.

We live in a world made of chemicals. Table salt is sodium chloride, sugar is a disaccharide, and vinegar is largely made of acetic acid. Knowing the naming system of chemicals can minimize confusion and chemical phobias. This tutorial introduces the naming of inorganic compounds in a systematic manner. The rules of naming simple cations, anions, and polyatomic ions are introduced first. Then, for the purpose of nomenclature, the inorganic compounds are separated into four categories: compounds of great ionic character, compounds of great covalent character, inorganic acids, and coordination compounds (presented in a separate link). The naming rules of each category are explained and illustrated with examples. A float chart at the end of the tutorial provides an easy step-by-step approach for the naming methodology. A link to the Tables of Common Polyatomic Ions illustrates 2-dimensional and 3-dimensional structures of some common polyatomic ions.

At Washington University in St. Louis, this tutorial is assigned to students before the first laboratory experiment is introduced. The naming of coordinate compounds is presented in a “satellite tutorial” linked to the original tutorial. This satellite tutorial is introduced to students later in the first semester of general chemistry laboratory when the experiments “Introduction to Coordination Chemistry” and “Preparation of Complex ions” are implemented.

Index


Bands, Bonds, and Doping: How Do LEDs Work?

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Authors: Rachel Casiday and Regina Frey

Key Concepts:  Bonding in elemental solids (metals, semimetals, and nonmetals); qualitative band theory; conductivity properties of elements.

Light-emitting diodes (LEDs) are pervasive in our lives. This tutorial provides explanations, in terms understandable by students with only a little high-school-chemistry background, for the differences in crystal structure, bonding, and band gaps that underlie the observed differences between metals, semimetals, and nonmetals. Band theory is taught qualitatively, and by comparing primarily the electronegativity of the elements in the solid. LEDs are semiconductor devices that convert electrical energy directly into light. Hence, the tutorial discusses semiconductor doping to explain the enhanced conductivity of the LED. Band gaps and diodes are discussed to describe how an LED emits light and what color of light an LED emits.

At Washington University in St. Louis, this tutorial accompanies the first laboratory experiment in General-Chemistry course, and therefore, it is used during the first weeks of general chemistry. In this first laboratory experiment, students explore the periodic properties and classify elements as metals, semimetals, or nonmetals. In one part of the procedure, students use LED-containing meters to test the conductivity of elements. In the lab manual, students learn that the conductivity properties of metals occur because valence electrons in metal atoms have a "sea" of empty space in which they can "swim". This picture is useful for understanding how metals have sufficiently mobile charged particles to conduct electricity, but it does not fully explain the differences between metals and other elements. To explain the behavior of metals, semimetals, and nonmetals (and to describe how LEDs work) we need to understand the bonding of solids in more detail.

The tutorial introduces many concepts that the students will not be expected to fully understand until later. Through exposure to simplified yet accurate explanations at this stage, students are motivated to probe into the chemical and physical bases underlying the phenomena they observe in their experiment. Later, when students learn about quantum mechanics, they will be rewarded to find that they already know a good deal about some of the applications of this theory, and will be able to refer back to this tutorial with greater understanding.

Index


Gas Laws Save Lives: The Chemistry Behind Airbags

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Authors: Rachel Casiday and Regina Frey

Key Concepts:  Reaction stoichiometry; ideal-gas law; Kinetic Theory of Gases; Newton's Laws.

The development of airbags began with the idea for a system that would restrain automobile drivers and passengers in an accident, whether or not they were wearing their seat belts. The road from that idea to the airbags we have today has been long, and it has involved many turnabouts in the vision for what airbags should be expected to do. The automobile industry started in the late 1950's to research airbags and soon discovered that there were more difficulties in the development of an airbag than anyone had expected. Crash tests showed that for an airbag to be useful as a protective device, the bag must deploy and inflate within 40 milliseconds. Once a sensor determines that a collision has occurred, an explosive reaction is triggered, generating nitrogen gas (N2). This gas fills a nylon or polyamide bag at a velocity of 150 to 250 miles per hour. In order for the airbag to cushion the head and torso with air for maximum protection, the airbag must begin to deflate (i.e., decrease its internal pressure) by the time the body hits it. Designing an airbag that meets these criteria requires both a macroscopic and a microscopic understanding of the behavior of gases.

This tutorial describes the chemistry and physics behind airbags. The chemical reactions that generate the gas used to fill the airbag are described, and students are required to balance them and calculate the amount of starting material required to fill the airbag in 40 ms. Macroscopic (ideal-gas law) and microscopic (kinetic theory of gases) pictures of gas behavior are explained in the context of the inflating airbag. Then, the mechanical principles that allow airbags to protect us in an accident are explained. Finally, students are asked to consider another aspect of airbag chemistry when they read about problems with undetonated-airbag disposal.

At Washington University in St. Louis, this tutorial accompanies a first-semester experiment on stoichiometry and the ideal-gas law in which oxygen gas is generated via photodecomposition. The students determine the value of the ideal-gas constant (R), and the composition of an unknown mixture containing an inert salt and an oxygen-producing substance.

Index


Phase Changes and Refrigeration: Thermochemistry of Heat Engines

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Authors: Rachel Casiday and Regina Frey

Key Concept:  One of the most important practical applications of the principles of thermodynamics is the heat engine. In the heat engine, heat is absorbed from a "working substance" at high temperature and partially converted to work. A refrigerator can be thought of as a heat engine in reverse. The cooling effect in a refrigerator is achieved by a cycle of compressing the nontoxic compound CCl2F2 (Freon), which condenses the Freon, and of expanding the Freon, which vaporizes it. The heat absorbed and released during these processes cools the refrigerator. Thus, in order to understand how refrigerators work, some knowledge of phase transitions is essential.

This tutorial provides both a molecular and a thermodynamic understanding of phase transitions. The refrigeration cycle, which involves phase transitions of Freon and the transfer of heat from the inside to the outside of the refrigerator, is described in detail. The questions in this tutorial require students to apply Hess's law to phase transitions, and to think about the molecular properties that would allow a substance to be a good refrigerant.

At Washington University in St. Louis, this tutorial accompanies a second-semester experiment about thermochemistry in which students measure the heat change of chemical reactions and use Hess's law to determine enthalpies of formation. The students use a calorimeter to measure the heat released by the neutralization of a sodium-hydroxide unknown with a hydrochloric-acid solution. Then they use this value to calculate the concentration of the sodium-hydroxide solution. They repeat this procedure for Mg and MgO.  Using Hess's law, the enthalpy of formation of MgO can be calculated.

Index


ADDITIONAL ONLINE TUTORIALS


Blood, Sweat, and Buffers: pH Regulation During Exercise

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Authors: Rachel Casiday and Regina Frey

Key Concepts:  Acid-base equilibria; equilibrium constants; buffering; Le Châtelier's Principle.

Many people today are interested in exercise as a way of improving their health and physical abilities. But there is also concern that too much exercise, or exercise that is not appropriate for certain individuals, may actually do more harm than good. Exercise has many short-term (acute) and long-term effects that the body must be capable of handling for the exercise to be beneficial. In particular, exercise initiates chemical changes in the blood which, unless offset by other physiological functions, cause the pH of the blood to drop. If the pH of the body gets too low (below 7.4), a condition known as acidosis results. This can be very serious, because many of the chemical reactions that occur in the body, especially those involving proteins, are pH-dependent. Fortunately, we have buffers in the blood to protect against large changes in pH. This tutorial describes, in detail, the most important pH buffer in the blood, the bicarbonate-buffer system, and briefly tells about some of the other pH buffers in the blood. To explain how buffers work, the tutorial uses both quantitative descriptions (e.g., equilibrium constants and titration curves) and qualitative descriptions (e.g., equilibrium shifts and Le Châtelier's Principle). The tutorial also shows how other organs in the body, such as the kidneys and the lungs, can help to control pH by removing components of the bicarbonate-buffer system that are present in excess. This tutorial is one of four blood-chemistry tutorials available for General Chemistry from Washington University in St. Louis.

At Washington University in St. Louis, this tutorial accompanies a second-semester acid-base titration experiment. In the experiment, students use phenolphthalein and a pH meter to determine the concentration and pKa of an unknown weak acid. Students generate a titration curve and describe acid-base equilibria quantitatively. The tutorial helps students apply this quantitative knowledge to a situation that is very relevant to most students (exercise), and enhances the students' quantitative understanding of equilibria with a qualitative viewpoint.

Index


Drug Strategies to Target HIV: Enzyme Kinetics and Enzyme Inhibition

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Authors: Rachel Casiday and Regina Frey

Key Concepts:   Catalysts; activation energy; Michaelis-Menten kinetics; enzyme inhibitors.

HIV, the virus that causes AIDS, is one of the hottest areas of medical research today. Researchers are seeking treatments for HIV-infected individuals, cures, and vaccines. So far, the most promising findings have been treatments to lessen the damage to the immune system from HIV; several treatments that have been developed have dramatically improved the outlook for many HIV patients. However, these treatments have many severe side effects, and in most cases are too costly to be administered widely in many parts of the world. Thus, more research is needed to improve the available treatments, making them more tolerable to patients and more accessible, and to continue the search for a cure for HIV and a vaccine, which would prevent the infection in the first place. To explain how these treatments help, the tutorial first discusses the immune cells that come under attack, and the mechanism by which the virus kills these cells if left untreated. HIV enters the cells of our immune system, replicates its genetic information, and produces new copies of itself, killing the host cells and infecting new ones. HIV requires certain enzymes to catalyze the reactions involved in infecting the body. Hence, if these enzymes could be turned off, then HIV would be unable to reproduce itself and continue an infection. This tutorial describes two of the most successful treatment options available today: reverse-transcriptase inhibitors (e.g., AZT) and protease inhibitors. These treatments interfere with enzymes that are needed for HIV to make copies of its genetic information and to cut its proteins to the proper size, two key steps in the virus's attack on the cells of the immune system. The tutorial explains the catalytic role of enzymes, and the Michaelis-Menten kinetic model, which has been developed to describe the rate of enzyme-catalyzed reactions. Finally, the tutorial explains how competitive and noncompetitive inhibitors work to block the action of enzymes, and shows how AZT and protease inhibitors are powerful enzyme inhibitors used in the fight against HIV.

At Washington University in St. Louis, this tutorial accompanies a chemical-kinetics experiment in which students determine the rate law for an inorganic reaction by studying the effect of substrate concentrations on the reaction rate. Students then explore the effect of temperature and a catalyst on the reaction rate. The tutorial shows students, using an example that students have heard about in the media, that catalysis is not as simple as it might at first seem, and that the catalyst itself can be inhibited in a number of different ways.

Index


Enzyme Kinetics: Carboxypeptidase

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Authors: Rachel Casiday and Regina Frey

Key Concepts:   Models of enzyme-substrate interaction; importance of molecular shape for catalysis.

The rate of many biological reactions is increased by enzymes, which are proteins that act as catalysts for specific reactions. For an enzyme to exert its effect on a substrate (i.e., a reactant in an enzyme-catalyzed reaction), the substrate must enter the active site of the enzyme to form the enzyme-substrate complex. In the lock-and-key model, the amino acids that make up an enzyme's active site in the unbound state are said to form a shape that exactly matches the shape of the substrate. This model is quite useful for visualizing how the enzyme-substrate complex is formed as a crucial step in catalyzing biological reactions. However, the active sites of many enzymes do not have a shape in the unbound form that exactly matches the shape of the substrate. The shape of the active site changes when the substrate binds to the enzyme, creating a shape into which the substrate fits. This concept, known as the induced-fit model, is used to describe the actual substrate-binding behavior of many different enzymes. One such enzyme is carboxypeptidase, which helps break down proteins, such as those from food, so that their constituent amino acids can be used to synthesize new proteins for the body. This tutorial explains the lock-and-key and induced-fit models of enzyme activity, and shows how carboxypeptidase is best described by the induced-fit model, because the shape of the active site changes when it binds to a substrate protein.

At Washington University in St. Louis, this tutorial accompanies a second-semester chemical-kinetics experiment in which students determine the rate law for an inorganic reaction by studying the effect of substrate concentrations on the reaction rate. Students then explore the effect of temperature and a catalyst on the reaction rate. The tutorial emphasizes that large molecules (e.g., proteins) can also act as catalysts and that the shape of a molecule is crucial in determining its ability to increase the rate of a reaction.

Index


I Have Seen the Light: Vision and Light-Induced Molecular Changes

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Authors: Rachel Casiday and Regina Frey

Key Concepts:   Electronic absorption spectroscopy; molecular orbitals; molecular structure and function; particle-in-a-box.

The vision process depends on the interaction of many different factors, such as the optics of the eye, the isomerization of retinal, nerve impulses, and the brain's ability to reconstruct the image.  But the fundamental processes underlying vision are the absorption of a photon by the retinal molecule, and the subsequent isomerization from 11-cis-retinal to all-trans-retinal.  The main chemical concept used in the vision process is the change in retinal's properties due to the change in the molecular orbitals (and therefore, the electron density) of retinal when it absorbs energy from photons that are reflected off of an object. When visible light hits retinal, a p electron is promoted to a higher-energy orbital, which results, approximately half the time, in the isomerization of retinal when the p electron returns to a lower molecular orbital. This isomerization of retinal forces a conformational change in the protein opsin and initiates a cascade of biochemical reactions resulting in a large potential difference across the plasma membrane of the photoreceptor cell.  This potential difference is passed along a nerve cell, as an electrical impulse, to the brain, which interprets the visual information.

This tutorial describes the vision process, the isomerization of retinal in terms of electronic absorption spectroscopy, the protein conformational changes, and the potential-difference buildup that generates the nerve impulse.  Both monochrome vision (rod cells) and color vision (cone cells) are discussed. The tutorial also emphasizes the relationship between protein structure and function and describes how retinal-containing proteins with different absorption spectra contribute to color vision.

At Washington University in St. Louis, students complete this tutorial in conjunction with a first-semester experiment in which they study the optical-absorption properties of conjugated dye molecules and analyze the results using the particle-in-a-box model. The students receive three (3) of four (4) cyanine dyes.  They must obtain the lmax for each of their unknown dyes using visible-light absorption spectroscopy, and determine which 3 of the 4 dyes in the series they have using the particle-in-a-box model.  Given the general form of the series, the students then must draw the structures of their 3 unknown dyes.

A common difficulty for students first encountering quantum theory is visualizing the changes in electron configuration as physical changes occurring in real molecules. This tutorial helps students to see how a real molecule, retinal, changes in response to absorption of an electron, and that this change has important consequences, i.e., vision.

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Freshwater Chemistry: Inorganic Reactions in the Water Supply

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Authors: Rachel Casiday and Regina Frey

Key Concepts:   Inorganic reactions; ions; precipitation.

The quality of freshwater is important for virtually every aspect of our lives, from drinking to industry to agriculture. It may be surprising to find that freshwater does not consist of pure water, but contains many dissolved ions. Many of these ions have no effect on our use of freshwater, others are essential for agriculture or health, and still others can be quite undesirable for the environment or human freshwater use (e.g., drinking water). Aqueous species in the water supply may also participate in reactions that generate a precipitate (e.g., calcium carbonate, which produces mineral deposits on cooking dishes, water pipes, and water boilers). These precipitates can cause damage to appliances and pipes and can result in loss of energy efficiency. Thus, a proper balance of these ions in the freshwater supply must be maintained, for the water to optimally serve both the environment and humans.

This tutorial explores two important aspects of the quality of the freshwater supply. In the first, students learn how acid rain is produced from inorganic reactions in the atmosphere, and reacts with soils and building materials to form soluble products, which wash away. In the second, students learn about water hardness, and how the ions in hard water react to leave the deposits associated with hard water. Ion-exchange columns are described as a way to remove hard-water cations from the water supply.

At Washington University in St. Louis, this tutorial accompanied a first-semester experiment in which the students begin to explore the area of chemical reactions. The students systematically classify inorganic aqueous solutions by conducting standard inorganic-reaction tests, which produce precipitate, color changes, or gas evolution.

Index


Treating the Public Water Supply:
What is in Your Water, and How is It Made Safe to Drink?

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Authors: Rachel Casiday, Greg Noelken, and Regina Frey

Key Concepts:   Aqueous solutions; solubility; solvation process for crystals; suspension; precipitation; ion-exchange reactions; physical separation techniques.

Water is perhaps the most important nutrient in our diets.  We need daily to replenish water that is lost from the body; but only 0.3% of the Earth's water supply is freshwater.  Furthermore, many freshwater sources are not suitable for humans to drink.  Hence, standards were provided by the Clean Water Act and the Safe Drinking Water Act to ensure that the population of the United States would have access to safe, usable water for drinking and other daily uses.  It may be surprising to find that freshwater does not consist of pure water, but contains many dissolved ions. Many of these ions have no effect on our use of freshwater, others are essential for agriculture or health, and still others can be quite undesirable for the environment or human freshwater use (e.g., drinking water).  This tutorial explains the chemistry involved in the processes used by our public-water facilities to treat our water and make it safe for us to drink and for other human uses.  These processes involve physical and chemical separation techniques; hence, the fundamental chemical principle in the treatment of water is solubility.  The tutorial also describes typical point-of-use water treatments, such as water softening and adsorption filters to remove undesirable contaminants (e.g., lead). The tutorial ends by describing the last step in the cycle of our public water: the re-entering of the used water to our freshwater supply.

At Washington University in St. Louis, this tutorial accompanies a first-semester experiment in which the students begin to explore the area of chemical reactions. The students systematically classify inorganic aqueous solutions by conducting standard inorganic-reaction tests, which produce precipitate, color changes, or gas evolution.

Index


NMR Analysis, IR Analysis and Smell Testing

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Authors: Regina F. Frey and Maureen J. Donlin

The detection of small molecules plays an important role in the survival of most animals, which use odor for identifying and evaluating their food, predators, and territory. For many years, scientists have been very successful in synthesizing fragrances. Many types of industry today have synthetic fragrances in their materials; for example, inks, paints, soaps, cleaning products, and foods. However, the detection and processing of odor by the body is not well understood. Despite the importance of olfaction (sense of smell) to our daily lives, the chemical aspect to olfaction was not given much attention by the scientific community until the 1980's.

Index


Acknowledgements:

The development of these tutorials was supported by grants from the Howard Hughes Medical Institute through the Undergraduate Biological Sciences Education program, Grant HHMI#71192-502004 and HHMI#71199-502008 to Washington University.

Copyright 1999, Washington University, All Rights Reserved. (Revised on 8/7/06)

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Revised On: 4/7/08