Determination of Reaction Rate Law from the Reaction of Crystal Violet with Sodium Hydroxide ______________________________________________
Abstract: This experiment helps determine the rate of reaction of crystal violet while it reacts with sodium hydroxide with respect to crystal violet. The amount of sodium hydroxide is varied in this experiment while crystal violet is kept at a constant. The transmittance of crystal violet is observed and recorded using a colorimeter and the data obtained is used to plot graphs which are manipulated using LoggerPro software to produce the desired outcome; rate of reaction of crystal violet. Upon completion of the experiment it was seen that the rate of reaction of crystal violet turned out to be 1 which meant the reaction was first order with respect to crystal violet. This was deduced upon plotting the graph of ln Absorbance versus time of crystal violet and by drawing the line of best fit, which showed that the slope graph was 1 which is the rate of reaction. This whole experiment was based upon the equation: Rate= k [CV+] [OH-], where k stands for the rate constant. Introduction: Kinetics, which is the study of how fast a reaction takes place or in other words the rate of a reaction, is the main ideology in this experiment. Reaction rates can be measured in a number of ways: by monitoring the amount of product formed, by measuring the loss in mass of reactants, for reactions involving gaseous products measuring the volume of gas produced, by electrolytic conductivity, pH measurement or for colored reactants or products measuring the transmittance by the use of a colorimeter. In this experiment the last method of measurement is used which is colorimetry. Colorimetry is a method of determining the kinetics of a reaction using a spectrometer which observes the amount of light that is absorbed or transmitted through a colored solution. As a reaction proceeds, the reactants either fades away or the product forms the color. By monitoring these changes the amount of product formed or reactant used up with respect to time can be monitored. The amount of light that is absorbed by a colored substance can be measured by calculating percentage absorbance or transmittance. A very helpful device known as colorimeter which is present in almost all equipped labs makes this quite simple to deduce. The machine displays the amount of light that passes through or absorbed by the substance. This instrument is based on the optics law or more commonly known as Beer-Lambert law, which is used in measuring the concentration of a solute in contrast to its absorbance. The colorimeter measures the wavelengths of different solutions as they vary. Distilled water is used as a reference in this experiment as it contains no colored elements and has a value of zero when inserted into the colorimeter. Crystal violet, a purple dye commonly used in inks or printers is reacted with sodium hydroxide, commonly known as caustic soda which is a powerful base. Sodium hydroxide is a colorless solution which when reacted with crystal violet causes it to lose its purple color and form a colorless product. The purpose of this experiment is to determine the order of the reaction with respect to crystal violet by using colorimetry. The amount of crystal violet is kept at a constant during the whole experiment while various amounts of sodium hydroxide, each of varying concentration are used. This method of determining rates is called the isolation method. Amount of reactant used with respect to time or the rate of reaction can be determined by plotting a graph of concentration versus time for the reactant if the reaction is first order. The slope is a measure of how much reactant is used per unit of time. As the concentration of reactant reduces in a chemical reaction, the slope is a negative value, hence by considering the absolute value of the slope, the rate of reaction of that reactant can be found for the...
References: 1. Atkins, P. W. (1978). Physical chemistry. San Francisco: W.H. Freeman.
2. Allen, J. P. (2008). Biophysical chemistry. Malden, MA: Blackwell Pub.
3. Lindon, J. C., Tranter, G. E., & Holmes, J. L. (2000). Encyclopedia of spectroscopy and spectrometry. San Diego: Academic Press.
Solution 1: Order 0, ǀRMSE/aǀ= 0.01641/0.271= 0.0605
Order 1, ǀRMSE/aǀ= 0.01129/0.271= 0.0416
Order 2, ǀRMSE/aǀ=0.3810/0.217= 1.4050
Solution 2, Order 1, ǀRMSE/aǀ=0.01566/0.134= 0.1169
Solution 3, Order 1, ǀRMSE/aǀ= 0.00693/0.492= 0.0141
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