PEC 247
Physical and Inorganic Chemistry
Experiment 1
The Rate of Hydrolysis of Ethyl Acetate
Hydrolysis of ethyl acetate if often a challenge since the acetate ion is a poor conductor compared
to that of the hydroxyl ion. This experiment is designed to find out what happens to the
conductance of a mixture of acetate and hydroxyl ions are contained in the one mixture by
measuring the mixture’s conductance at appropriate intervals. From this a constant can be
calculated to be compared with an accepted value for the conductivity of a acetate/ hydroxyl
reaction.
The reaction taking place is by the equation:
CH3CH2OOCCH3 + OH- ↔ CH3CH2OH + CH3COOThis reaction follows second order kinetics where the rate of formation is given by:
𝑑[𝐴𝑐]
= k[OH-][EtAc]
𝑑𝑡
Method:
Experiment preformed as detailed in Laird1
Results:
Calculations:
Example calculations for each column
𝐊𝐨−𝐊𝐭
𝐊𝐭−𝐊∞
: Where Ko= 2.5, K∞=1.15
2.5−1.88
At 10 minutes=1.88−1.55 =0.738
2.5−1.60
2.5−1.45
At 20 minutes=1.60−1.55=1.607At 30 minutes=1.45−1.55=2.56
𝟏
𝐚𝐭
where a is concentration in mol L-1 and t in seconds:
𝟏
At t=10 : 𝟎.𝟎𝟐𝟓 𝒙 𝟔𝟎𝟎=0.067
𝟏
At t=20=𝟎.𝟎𝟐𝟓 𝒙 𝟏𝟐𝟎𝟎=0.033
PEC 247
Physical and Inorganic Chemistry
K (Lmol-1s-1):
𝐊𝐨−𝐊𝐭
𝐊𝐭−𝐊∞
𝟏
X 𝐚𝐭
At t= 10 minutes
= 0.738 x 0.067
=0.049
Table 1: shows conductivity values at regular intervals for a hydroxyl and acetate mixture.
Time (minutes)
Kt(mS)
Water
0.00194
Initial (OH- only)
2.83
0
K(Lmol-1s-1)
Ko-Kt /Kt-K∞
1/at
2.50
0
0
10
1.88
0.738
0.067
0.049206
20
1.60
1.607
0.033
0.053571
30
1.45
2.560
0.022
0.056911
40
1.37
3.424
0.016
0.057071
50
1.31
4.407
0.013
0.058765
60
1.27
5.348
0.011
0.05942
80
1.21
7.588
0.008
0.063235
100
1.17
10.23
0.006
0.068205
120
1.15
12.27
0.005
0.068182
Day after (10am)
1.045
0
0.0007
0
0
Average= 0.049
Percentage error:
𝟎.𝟏𝟏−𝟎.𝟎𝟒𝟗
=
𝟎.𝟏𝟏
=55.45%
x100
PEC 247
Physical and Inorganic Chemistry
Discussion:
As comparing the accepted value to our experimental value it is clear that since there is an error greater
than 50% it must mean there were a few errors that had not been overcome or were not carefully taken of
such as how clean the glassware was or how accurate or old the conductimetre is i.e. the age of the
electronics within the machine. Another could have been incorrect measurement of the mixture such as too
much water or too much solution when its concentration was being prepared. Another could have been
contaminants within the cell or on the probe
However it was observed that over time the conductivity decreased as the reaction precede this would have
been because the number of ions in solution was decreasing over time and therefore the conductivity of the
reaction was also decreasing. Comparing the initial conductivity i.e. the solution of only 0.025 M OHrecorded a reading of 2.83 mS and once the acetate was added it immediately dropped to 2.5 mS which
would mean ions were being removed from solution just as soon as the reaction started taking place or the
products had a lower conductivity compared to the initial recorded conductivity of the reactants.
Conclusion:
Hydrolysis of acetate reacting with the hydroxide showed that over time the conductivity decreased proving
that as the reaction went forward the number of ions in solution which allows for higher conduction
decreased. However as it was seen the comparison between the accepted and our calculated revealed a
number of errors that could of been possible to project such a difference between accepted and
experimental conductivity values.
References:
PEC247 Physical and Inorganic Chemistry Laboratory Manual, Murdoch University
Atkins. Peter, De Paula. J, ATKINS’ PHYSICAL CHEMISTRY, W.H Freeman and company United states