1. Experiment 12
Kinetics – Hydrolysis of
2-chloro-2-methylpropane

2. 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

3. Introduction
Hydrolysis of 2-chloro-2-methylpropane is an example of a substitution reaction
Hydroxide attacks the carbocation after chlorine dissociates from the molecule

4. 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

5. Introduction Hydrolysis of 2C2MP is dependant on the [reagent] only
Rate is directly proportional to [reactant]
k is the rate coefficient

6. 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

7. 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

8. 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

9. 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)

10. 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

11. 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 reaction

12. Results & Calculations
Calculate the rate coefficient k from
Calculate k at each of the three temperatures – can then use Arhennius eqn to plot a graph giving EA/R as slope

13. Arhennius equation
A graph of ln k against 1/T gives a line with slope –EA/R and intercept of ln A

14. Drawing the graph Graph must fill the page
Label the axes, include units and values on the axes
Plot the data as a point surrounded by a small circle that represents the possible error
Draw a straight line which best fits the data points
Use points from either end of the line to calculate the slope – minimizing the error

15. Report Introduction Observations Results & Calculations Graph
Discussion & Conclusions

16. Physical Chemistry Section
NO PRE-PRACTICAL TALKS FOR THE NEXT 4 PRACTICALS
This week and next week you will be in your usual labs
The 3 weeks thereafter you will rotate between the experiments from week to week
Hand your reports your usual demonstrator as before