Chemical kinetic experiments to determine rate laws are common in high school and college chemistry courses. For reactions involving a color change, rate laws can be determined experimentally using spectrophotometric or colorimetric equipment though this equipment can be cost prohibitive. Previous work demonstrated that inexpensive handheld camera devices can be used to quantify the concentration of a colored analyte in solution. This paper extends this approach to the kinetic study of the color fading of crystal violet upon reaction with sodium hydroxide. The results demonstrate accurate determination of the reaction order, with respect to crystal violet, using a method accessible in many high school and college laboratories. M ost high school and college students have some practical knowledge about speeds of reactions before taking a chemistry course. For example, students understand that foods cook faster at higher temperature. This knowledge is supported and extended by the study of chemical kinetics. While studying kinetics, students learn that rate laws for chemical reactions can only be determined experimentally. Experiments suitable for exploration of kinetic concepts are essential for building connections to the curriculum. Rate laws can be determined by measuring initial rates or monitoring concentration over time.Monitoring changes in concentration of a colored analyte in solution can be accomplished through spectrophotometry or colorimetry. Traditional equipment used for these measurements can cost hundreds to thousands of dollars per instrument; many high schools do not have the financial means to purchase such instrumentation. Recently, Kehoe and Penn published a method for performing quantitative colorimetry using handheld camera devices. 1 Their work demonstrated suitable precision and accuracy; thus, quantitative colorimetry can be performed even in the absence of traditional equipment.Crystal violet, an intensely violet-colored triphenylmethane dye, reacts with hydroxide ions in aqueous solution to form a colorless compound (Scheme 1). For years, this reaction has been successfully used as a lab exercise for the experimental determination of a rate law. 2,3 A large excess of sodium hydroxide relative to crystal violet is used, which means that the reaction's rate depends only on the concentration of crystal violet. Analytical spectrophotometry or colorimetry is performed at specified time intervals. Students monitor the concentration of crystal violet, which fades over time, by Scheme 1. Reaction Scheme between Crystal Violet and Hydroxide Ions a a Structures (a) and (b) are two resonance structures of crystal violet before the reaction, and structure (c) is the colorless product of the reaction.Laboratory Experiment pubs.acs.org/jchemeduc

Spectrophotometry and colorimetry experiments are common in high school and college chemistry courses, and nanotechnology is increasingly common in every day products and new devices. Previous work has demonstrated that handheld camera devices can be used to quantify the concentration of a colored analyte in solution in place of traditional spectrophotometric or colorimetric equipment. This paper extends this approach to quantifying the concentration of gold nanoparticles in a colloidal gold "dietary supplement". With the addition of free Google applications, the investigation provides a feasible, sophisticated lab experience and introduction to nanotechnology.

With new K−12 national science standards emerging, there is an increased need for experiments that integrate engineering into the context of society. Here we describe a chemistry experiment that combines science and engineering principles while introducing basic polymer and green chemistry concepts. Using medical sutures as a platform for investigating polymers, students explore the physical and mechanical properties of threads drawn from poly(ε-caprolactone) samples of different molecular masses and actual purchased absorbable and nonabsorbable medical sutures. An inquiry-based part of the experiment tasks students with designing their own experiment to probe the potential of melt blending poly(ε-caprolactone) with commercially available polylactide products in order to modify the properties of the "sutures" drawn. Through these lessons students gain an appreciation for the importance of plastics in our society and how scientists are working to develop more sustainable alternatives. Overall, this laboratory experiment provides a feasible, versatile, sophisticated laboratory experience that engages students in a relatable topic and meets many of the Next Generation Science Standards.

The recent increased public interest in forensic science, sparked in part by television shows such as CSI and Bones, presents an opportunity for science educators to engage students in forensic chemistry-themed activities to introduce fundamental concepts, such as the scientific method. In an outreach setting, mysteries were used as a way to engage middle school students to select forensics tests, form hypotheses, make observations while conducting the tests, consider positive and negative controls, and use the results to reach conclusions. Student data shows that the outreach activities generally increase student understanding of the scientific method. These activities have been translated from outreach activities into accessible activities for middle and high school classrooms.

A versatile experiment is described for the high school and college laboratory setting based on the synthesis of biobased polymers prepared from inexpensive, renewable, and nonhazardous chemicals. Combinations of readily available citric acid, glycerol, and tapioca root starch are used to prepare three polymeric materials with different observable physical properties. Simple qualitative comparisons of aqueous degradation rates can be made or a dye can be added for quantitative assessment. Food and Drug Administration (FDA) approved Yellow Dye No. 5 is selected as a dye stable to basic conditions and is added to each sample in the form of commercial food coloring. The dyed polymer samples are observed to degrade in an aqueous sodium hydroxide solution, releasing the dye. Both ultraviolet–visible spectroscopy and smartphone colorimetry are used to follow the increasing dye concentration, which is inversely correlated to polymer degradation. The collected data is suitable for analysis and graphing by students. Potential learning outcomes of the experiment include Le Chatelier’s principle, types of intermolecular forces, hydrolysis, absorption spectroscopy, Beer’s Law, rate determinations, and graphing. The experiment models green chemistry principles of design for safer chemicals, degradation, and use of renewable feedstocks. Paramount to the educational objectives of the curriculum are the societal connections to plastics that are accumulating in the environment and causing harm, as well as examples of successful advances in commercial bioplastics such as poly­(lactide) (PLA).

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