This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: 1 A SAMPLE REPORT Activation Energy: Enzyme-Catalyzed Hydrolysis of Sucrose Abstract The kinetics of the inversion of sucrose by the invertase enzyme was explored at several temperatures using a polarimeter. The first order rate constants for the inversion were determined to be 0.065 +/- 0.001 min-1 , 0.095 +/- 0.002 min-1 , and 0.135 +/- 0.006 min-1 at 300K, 310K, and 320K respectively. The temperature dependence of the rate constant followed Arrhenius behavior and resulted in an activation energy of 29.2 +/- 0.2 kJ/mol in good agreement with the literature value of 31.4 kJ/mol. Introduction The activation energy and the rate of reaction for the invertase-catalyzed hydrolysis of sucrose will be measured by following changes in optical rotation of an aqueous solution of sucrose and invertase. When sucrose is hydrolyzed to a mixture of glucose and fructose, the optical rotation changes from clockwise (+) to counter clockwise (-). C 12 H 22 O 11 ( + ) rotation 1 2 4 3 4 + H 2 O invertase C 6 H 12 O 6 + C 6 H 12 O 6 ( ) rotation 1 2 4 4 4 4 3 4 4 4 4 (1) The rotation will be monitored with an optical polarimeter and then used to calculate the amount of sucrose left unhydrolyzed. The angle of rotation is determined at the beginning of the experiment ( ) and at equilibrium ( ) . The algebraic difference ( - ) is a measure of the original sucrose concentration. The concentration of H 2 O during the reaction remains essentially constant, since H 2 O is present in large excess. The reaction is known to be first order in sucrose, 1-6 thus the concentration of sucrose as a function of time should follow the relationship ln C t C = kt (2) where C is the initial concentration of sucrose when the reaction mixture is first placed in the polarimeter and C t is the sucrose concentration at time t after the addition of invertase. Since C t is proportional to ( t- ) and C (a constant) is proportional to ( - ) , the rate constant k can be determined from a plot of ln( t- ) versus time. 4-6 The rate constant k depends on the absolute temperature T via the Arrhenius Equation k = Ae E a RT (3) where E a is the activation energy. Thus if the rate constant is determined at several different temperatures, the activation energy can be determined via a modification of Equation (3) by plotting lnk versus 1/T . ln k = lnA E a RT (4) Once the plot is constructed the slope can be used to calculate the activation energy as follows. 2 E a = -Rslope (5) The data treatment consists of determining the rate constants for the invertase-catalyzed hydrolysis of sucrose at three different temperatures followed by determining the activation energy from an Arrhenius Plot ( lnk versus 1/T )....
View Full Document