Kinetics of Crystal Violet Color Fading via a Small Footprint Diode Array Spectrometer
Abstract
Crystal violet is a pH indicator and is commonly used to classify bacteria. In acidic solutions, crystal violet is yellow in color and at approximately the pH of 1.6, it transitions to a violet color. Over time, this violet color fades as it reacts with the CO 2 in the air until it is clear. A small footprint visible-near- infrared spectrometer (Vis-NIR) with diode array detector was employed in this investigation. Using the software that operates the spectrometer, the absorbance of crystal violet solutions can be measured at 585 nm at high concentrations of base as a function of time. The results from the experiment are copied and pasted into excel for additional analysis. The order can then be determined with respect to fading of the violet color. The rate law for this reaction is determined to be first order, due to the linear curve achieved when plotting ln(Abs) as a function of time. Conducting the experiment at two relatively high concentrations of base permits the calculation of the overall rate law for the reaction of crystal violet and base.
Kinetics of Crystal Violet Color Fading via a Small Footprint Diode Array Spectrometer
Crystal violet is a pH indicator and is commonly used to classify bacteria. In acidic solutions, crystal violet is yellow in color and at approximately the pH of 1.6, it transitions to a violet color. Over time, this violet color fades as it reacts with the CO 2 in the air until it is clear. A small footprint visible-near- infrared spectrometer (Vis-NIR) with diode array detector was employed in this investigation. Using the software that operates the spectrometer, the absorbance of crystal violet solutions can be measured at 585 nm at high concentrations of base as a function of time. The results from the experiment are copied and pasted into excel for additional analysis. The order can then be determined with respect to fading of the violet color. The rate law for this reaction is determined to be first order, due to the linear curve achieved when plotting ln(Abs) as a function of time. Conducting the experiment at two relatively high concentrations of base permits the calculation of the overall rate law for the reaction of crystal violet and base.