Experiment 12.ppt

Objectives Determine the rate coefficient for the hydrolysis of 2-chloro-2-methylpropane To use the Arrhenius equation Determine the activation energy for the hydrolysis of 2-chloro-2-methylpropane Introduction Hydrolysis of 2-chloro-2-methylpropane is an example of a substitution reaction Hydroxide attacks the carbocation after chlorine dissociates from the molecule Introduction The rate of a reaction is the change in reagent/product conc. over time By measuring the concentration of reagents/products at various points during the reaction the rate can be obtained Introduction Hydrolysis of 2C2MP is dependant on the [reagent] only Rate is directly proportional to [reactant] k is the rate coefficient Introduction The rate law indicates that the reaction depends on [reactant] The reaction is first order In this case k has units of s-1 Introduction Rate laws can provide much information regarding the mechanism of reactions The rate-[reactant] relationship must be determined experimentally Manipulation of the rate law gives Experimental Perform the hydrolysis reaction at three different temperatures and note the time taken for each reaction We can thus calculate the rate coefficient and the activation energy for the reaction Experimental Pipette 3 ml of 0.1 M 2C2MP solution to a test tube Pipette 0.3 ml of 0.1 M NaOH solution into another test tube and add 6.7 ml of water Add 2 drops of bromophenol blue indicator Clamp in a water bath/ice bath and record the temperature and exact time (t0) Experimental Add the 2C2MP soln to the NaOH soln and swirl to ensure complete mixing When the indicator turns from blue to yellow record the reaction time Repeat twice – values should be within 10% of each other – and get the average Experimental Perform the hydrolysis reaction at room temperature, in an ice/water bath and in a water bath at ~35°C Knowing the rate coefficient at three temperatures allows us to use the Arhennius equation to calculate the activation energy of the reac