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In the Kinetics of Crystal Violet Fading Inquiry Lab Solution for AP® Chemistry, students use spectroscopy methods and graphical analysis to determine the rate law for the reaction of crystal violet with sodium hydroxide.
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Big Idea 4, Investigation 11, Primary Learning Objective 4.2
Crystal violet is a common, beautiful purple dye. In strongly basic solutions, the bright color of the dye slowly fades and the solution becomes colorless. The kinetics of this “fading” reaction can be analyzed by measuring the color intensity or absorbance of the solution versus time to determine the rate law. In this advanced-inquiry lab, students use spectroscopy and graphical analysis to determine the rate law for the color-fading reaction of crystal violet with sodium hydroxide.
First, students construct a calibration curve of absorbance versus concentration for crystal violet using a series of known or standard solutions. This procedure provides a model for students to design experiments to determine the order of reaction with respect to both crystal violet and sodium hydroxide. Two dyes with similar structures, malachite green and phenolphthalein, are provided for optional extension or cooperative class inquiry studies.
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Complete for 24 students working in pairs. A spectrophotometer or colorimeter as well as common laboratory equipment is required and available separately. A refill kit for the Kinetics of Crystal Violet Fading Advanced Inquiry Laboratory Kit is also available. A version of this lab is available as a Wet/Dry Advanced Inquiry Laboratory Kit for One Period (Catalog No. AP9475).