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.