Undergraduate Chemistry Laboratory Research Articles

The Solubility Product of PbCl2 from Electrochemical Measurements

A new experiment suited for an undergraduate physical chemistry laboratory is presented. The students obtain the solubility product, Ksp, of PbCl2 at various temperatures from practically simultaneous emf measurements on two electrochemical cells. One half-cell is common to both cells. Each of the three half-cells is enclosed in a jacket of circulating water where the temperatures are controlled to better than ±0.05 K and measured to ±0.1 K. A 1 M KNO3 salt bridge is used in the two cells. At each temperature the difference between the two cells' emf values is directly related to the concentration of the Cl- ions in the saturated PbCl2 solution, which in turn yields the solubility product of PbCl2. The variation of ln Kspwith T-1 yields the standard enthalpy and entropy of the solubility equilibrium of PbCl2(s). Use of two cells to cancel out the temperature dependencies of the standard reference electrodes and junction potentials across the salt bridge is novel. This experiment is not found in physical...

Incorporating Automation in Undergraduate Laboratories

Automated techniques and philosophies, which have become increasingly important in modern laboratories, are not traditionally covered in undergraduate chemistry curricula. To this end, we have been incorporating automated sample preparation methods using standard robotic workstations in our undergraduate analytical chemistry laboratory. Using a Benchmate™ II Workstation, an automated method has been developed and implemented for the solid phase extraction of capsaicins from commercial hot pepper sauces prior to liquid chromatographic analysis. This paper reports on pedagogical aspects of incorporating automation into the undergraduate curriculum as well as results obtained for manual and automated extractions conducted by students.

Incorporating Automation in Undergraduate Laboratories

Automated techniques and philosophies, which have become increasingly important in modern laboratories, are not traditionally covered in undergraduate chemistry curricula. To this end, we have been incorporating automated sample preparation methods using standard robotic workstations in our undergraduate analytical chemistry laboratory. Using a Benchmate™ II Workstation, an automated method has been developed and implemented for the solid phase extraction of capsaicins from commercial hot pepper sauces prior to liquid chromatographic analysis. This paper reports on pedagogical aspects of incorporating automation into the undergraduate curriculum as well as results obtained for manual and automated extractions conducted by students.

Study of Polymer Glasses by Modulated Differential Scanning Calorimetry in the Undergraduate Physical Chemistry Laboratory

Recent technological advances in thermal analysis present educational opportunities. In particular, modulated differential scanning calorimetry (MDSC) can be used to contrast reversing and nonreversing processes in practical laboratory experiments. The introduction of these concepts elucidates the relationship between experimental timescales and reversibility. The latter is a key concept of undergraduate thermodynamics theory that deserves reinforcement. In this paper, the theory and application of MDSC to problems of current interest is outlined with special emphasis on the contrast between crystallization and vitrification. Glass formation deserves greater emphasis in the undergraduate curriculum. Glass transitions are increasingly recognized as an important aspect of materials properties and dynamics in fields ranging from polymer science to protein folding. The example chosen for study is a comparison of polyethylene glycol and atactic polypropylene glycol. The experiment is easily performed in a typi...

Simple Recipes for Prebiotic Soup: A High School or Undergraduate Chemistry Laboratory

A lab activity demonstrating Stanley Miller‘s prebiotic soup experiments is described. This lab activity, which uses only simple, readily available materials and equipment, would be suitable for us...

Identifying a Protein by MALDI-TOF Mass Spectrometry: An Experiment for the Undergraduate Laboratory

Matrix-assisted laser desorption ionization time-of-flight (MALDI–TOF) mass spectrometry has become a valuable tool for performing routine biochemical analyses. A common procedure for protein identification involves using tryptic digestion to obtain masses of individual peptides derived from the protein. The masses are compared against an online database, and probability-based scoring systems are used to determine the closest protein matches. This article describes an experiment we have developed for an undergraduate honors general chemistry laboratory to introduce students to state-of-the-art mass spectrometric methods. Students are given an overview of the theory and instrumentation associated with MALDI–TOF, and gain hands-on experience with Internet tools for protein identification using mass spectral data. The experiment would be suitable for upper-division undergraduate laboratory courses as well; appropriate modifications for this purpose are also described.

Cost-Effective Spectroscopic Instrumentation for the Physical Chemistry Laboratory

Teaching or developing experiments for an undergraduate physical chemistry laboratory course can be very challenging. Often it is difficult to develop particular experiments because the spectroscopic instrumentation is not readily available within your department or is too expensive to purchase for an undergraduate laboratory experiment. To address these issues, we purchased a series of modular miniature UV–vis fiber-optic spectrometers from Ocean Optics Inc. to conduct undergraduate physical chemistry laboratory experiments. The instrumentation is very modular and can be used for a variety of absorption, emission, or Raman scattering experiments. Instrumentation can also be used in a standard undergraduate instrumental analysis course. The physical chemistry laboratory experiments that we developed with this new instrumentation consist of analyzing the Balmer emission lines of the hydrogen atom, studying nitrogen emission band lines, investigating the absorption spectrum of iodine, and analyzing the Rama...

Efficient Separation of Yolk from White in Boiled Chicken Eggs Leads to Convenient Extraction of Biologically Viable Phosphatidylcholine Lipids

In this biochemistry exercise, students investigate the technological and economic advantages and disadvantages of extracting phosphatidylcholine from boiled and raw chicken eggs. A number of analytical techniques are employed to isolate, purify, identify, and structurally characterize the product, to quantify yields (typically 40% relative to the theoretical maximum), and to assess the efficiency of the method. Students are exposed to several modern spectroscopic instruments, and for a deeper understanding of bioorganic chemistry they must employ engineering skills to assess the practicality of one method over another. It is intended that this material be considered as experimental course-work in undergraduate biochemistry and chemistry laboratories.

Quantifying Meniscus Forces with an Electronic Balance: Direct Measurement of Liquid Surface Tension. A Physical Chemistry Experiment

The phenomenon of capillary adhesion, in which a drop of liquid placed between two solid surfaces attracts them together, is considered at an elementary level. It is shown that for a small amount of liquid, independent of the solids-contact geometry, the adhesion force is defined mainly by the Laplace pressure force FL, for which a generalized equation is derived under arbitrary contact geometry. A simple physical chemistry laboratory experiment for measuring FL between a glass sphere and a glass plate with an ordinary electronic balance is described. The relationship between FL and liquid surface tension γ is used to obtain γ. The validity and acceptability of this method for undergraduate physical chemistry laboratories is experimentally confirmed for various liquid samples.

Synthesis and Characterization of a Hyperbranched Copolymer

This experiment involves the cationic ring-opening copolymerization of glycidol (2,3-epoxy-1-propanol) with propylene oxide and is suitable for undergraduate polymer chemistry or advanced organic synthesis laboratory courses. Students are introduced to hyperbranched polymers and learn how to use a combination of analytical techniques in constructing a coherent picture of polymer structure. The reaction mechanism involves active participation by the hydroxyl functional group (of glycidol) in a cationic polymerization, from which protic species are usually, but not always, excluded. This critical feature, which is responsible for the extensive branching in the polymer, helps students learn the difference between the so-called "active chain end" and "activated monomer" propagation mechanisms. The short, straightforward synthesis, which uses commonly available laboratory equipment and commercially available chemicals, is carried out at room temperature and proceeds in high yield. GC monitoring of the reaction and NMR and FTIR analysis yield information about polymer structure and confirm chain branching. The stable polymer product is checked for solubility and further examined by gel permeation chromatography and differential scanning calorimetry, yielding results consonant with the structural information gained by spectroscopic means.

Sacarose no laboratório de química orgânica de graduação

An experiment showing the readily available disaccharide (sucrose) as reagent for experiments in undergraduate chemistry laboratory is described. The preparation of 2,3:4,5-di-O-isopropylidene-b-D-fructopyranose from sucrose is very simple, uses low cost materials, requires two periods of 4 hours and is useful for classroom support in undergraduate courses.

Integration of Environmental Analytical Chemistry with Environmental Law: The Development of a Problem-Based Laboratory

Environmental chemists face difficult challenges related to generating, interpreting, and communicating complex chemical data in a manner understandable by nonchemists. For this reason, it is essential that environmental chemistry students develop the skills necessary not only to collect and interpret complex data sets, but also to communicate their findings in a credible manner in nonscientific forums. Key to this requirement is an understanding of the quality assurance/quality control (QA/QC) elements used to support specific findings. This paper describes the development of a problem-based undergraduate environmental analytical chemistry laboratory and its integration with an undergraduate environmental law course. The course is designed to introduce students to the principles of performance-based analytical methods and the use of environmental indicators to perform environmental assessments. Conducting a series of chemical and toxicological tests, chemistry students perform an environmental assessment on the watershed of the mythical City of Rowan. Law students use these assessments to develop legal arguments under both the Safe Drinking Water Act and the Clean Water Act.

Nanostructures in Physical Materials Chemistry: An Exploratory Laboratory

The blend of nanotechnology and material science is often beyond the scope of undergraduate laboratories. Through undergraduate research, graphite-intercalated compounds have been incorporated in the production of carbon-based nanostructures. Based on this work a series of exploratory exercises were designed for the undergraduate physical chemistry laboratory emphasizing nanostructure material science. This rapidly expanding area of science and technology can be introduced at an undergraduate level using a high temperature oven to produce nanostructure samples that are analyzed by Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy at research university laboratories, infrared spectroscopy, and a bomb calorimeter. In these experiments we use samples of pure graphite, fluorinated graphite, and lanthanum oxide to induce the formation of nanostructures. An overview of fullerenes, nanotubes, boron nitride and Si nanostructures, other carbon forms, graphite-intercalated compounds, and the storage of hydrogen in nanotubes are provided in an appendix. Several extensions of the laboratory are proposed.

Measurement of the Bulk Modulus of a Liquid Using a Pump?Probe Laser Technique

We describe an undergraduate laboratory experiment that uses a time-resolved laser technique. Using pump-probe in a novel way, students determined the bulk modulus of a liquid. Employing the fourth harmonic from a pulsed Nd:YAG laser, an elastic wave is generated in an aqueous solution of N-acetyltryptophan, and the wave propagation is probed by a He-Ne laser. This experiment serves as a rare example of how a bulk property of a condensed phase can be measured using time-resolved optical measurements having relevance to undergraduate physical chemistry or material science laboratory.

Teaching the Fundamentals of Pulsed NMR Spectroscopy in an Undergraduate Physical Chemistry Laboratory

Pulsed nuclear magnetic resonance (NMR) spectroscopy has become the premiere technique for chemists and biochemists studying the conformational, structural, and dynamic properties of a wide variety of molecular and biological systems. The theories and physical concepts associated with pulsed NMR spectroscopy are difficult for undergraduate students to comprehend and often require a thorough understanding of spin physics. Additionally, undergraduates in a laboratory course often consider a pulsed NMR spectrometer to be a "black box" and do not really understand how it operates. To address these issues, we developed an undergraduate physical chemistry laboratory experiment that utilizes a commercially available bench-top pulsed NMR spectrometer. In this experiment, the students assemble the components of an NMR spectrometer, program a variety of pulse sequences, and collect T1 and T2 relaxation data.

Binary Solid-Liquid Phase Diagrams of Selected Organic Compounds. A Complete Listing of 15 Binary Phase Diagrams

The investigation of multicomponent solid-liquid equilibria is of considerable importance in chemistry and materials science. Thus the determination of phase diagrams is a standard experiment in most undergraduate physical chemistry laboratory courses. This article proposes a simple and low-cost apparatus that allows accurate and reproducible measurements in a broad temperature range. Fifteen solid-liquid phase diagrams of binary systems that result from the systematic combination of six aromatic hydrocarbons are summarized. The aromatic hydrocarbons selected are easily accessible and melt in a convenient temperature range. The phase diagrams can be described within the experimental accuracy by the theoretical behavior of ideal systems with no solid solubility. This material is particularly well suited for a laboratory course, to illustrate the concepts of inhomogeneous equilibria with a large number of systems.

Modular Spectrometers in the Undergraduate Chemistry Laboratory

A rapid evolution of fiber-optic and computer technology led to the concept of modular spectrometers. The Ocean Optics S2000 series of spectroscopic instruments, based on a 2048-element linear CCD-array, are examples of such equipment. We have introduced two of these modular systems into our undergraduate laboratory courses, for experiments that serve as an introduction to signal processing. The Ocean Optics spectrometers have proven to be both rapid and inexpensive and have improved the quality of learning of our students.

An Experiment on Photochromism and Kinetics for the Undergraduate Laboratory

An experiment on photochromism and photochemical kinetics for the undergraduate physical chemistry laboratory is presented. Solutions of the photochromic compound 1',3'-dihydro-1',3',3'-trimethyl-6-nitro- spiro(2H-1-benzopyran-2,2'-2H-indole) (referred to as 6-NO2-BIPS) are irradiated with UV light, inducing a change of color by photoisomerization of the closed-ring isomer (N) to an open-ring isomer (the merocyanine isomer, MC). The thermal back-isomerization from MC to N is followed by recording the absorbance decay of MC in the visible region. Relaxation times at different temperatures were obtained and the activation energy and entropy calculated for the back isomerization. The value of ΔH° for the thermal equilibrium was calculated by measuring the changes of the UV absorbance of N and the visible absorbance of MC when temperature is varied. The system presents very strong solvent effects, which are illustrated by comparing the remarkable differences of the 6-NO2-BIPS photochromism in ethanol and tolu...

An EPR Experiment for the Undergraduate Physical Chemistry Laboratory

An experiment that illustrates the principles of electron paramagnetic resonance spectroscopy in the undergraduate physical chemistry laboratory is described. Students measure the value of g for DPPH and use it to determine the value of g for two inorganic complexes, Cu(acac)2 and VO(acac)2. The students use two instruments: an instructional device that illustrates the principles of EPR and a commercial Varian E4 spectrometer. This approach allows an elucidation of the principles of the method and provides experience with a more sophisticated research-grade instrument.

Teaching Sample Preparation in the Undergraduate Laboratory

Teaching sample preparation in an undergraduate analytical chemistry laboratory provides many challenges. For example, the time required to properly digest a sample means that sample preparation and method development are often deliberately overlooked in the undergraduate laboratory. To teach sample preparation, we have developed an experiment for the acid digestion of an iron ore sample in a microwave oven. From a pedagogical perspective, the microwave oven has the advantage of allowing easy control of experimental parameters such as heating power and time. This experiment requires two 3-hour lab periods. One lab period is required for determining the optimum conditions to achieve maximum extraction of Fe from an iron ore sample. The digestion parameters used for this experiment are choice of acid, digestion time at a fixed microwave power, and microwave power at a fixed time. A second lab period is required for the preparation of calibration standards and the analysis of the ore samples for Fe using flame atomic absorption spectroscopy. Using the optimum digestion parameters, Fe was measured in a known ore sample and was within 2% of the expected concentration.