TABLE OF CONTENTS
ABSTRACT........................................................................................................................................ 2
INTRODUCTION .............................................................................................................................. 3
THEORY ............................................................................................................................................ 4
EXPERIMENTAL PROCEDURE ..................................................................................................... 6
EXPERIMENTAL RESULTS............................................................................................................ 7
DISCUSSION ................................................................................................................................... 11
CONCLUSION ................................................................................................................................. 12
RECOMMENDATIONS .................................................................................................................. 12
REFERENCE.................................................................................................................................... 13
ABSTRACT
This experiment was done to determine the rate law expression of reaction of Ethyl Acetate
with sodium hydroxide. Due to sequence of reactions conducted in this experiment, hydrolysis
reaction of Ethyl acetate with sodium hydroxide (Saponification) was carried out in a Batch
reactor at Standard Temperature and Pressure conditions. Hydrolysis defines chemical
decomposition involving bond breakdown and subsequently addition of elements of water.
Four tests were carried out varying reactants concentrations, at each pair of the concentration
values, different values of rate constant were obtained at various time and concentration data.
Concentration of the mixtures was measured as electrical conductivity as a function of time at
the same temperature of 25oC. Amongst multiple methods for determining rate law expressions
for chemical reactions, the method of initial rates was used to determine the rate law for the
reaction in this practical. Graphs of conductivity against time were plotted to aid in determining
the rate law for the reaction using method of initial rates.The method of initial rates allows the
values of reactants order of reaction to be found by running the reaction multiple times under
controlled conditions and measuring the rate of the reaction in each case. All variables are held
constant from one run to the next, except for the concentration of one reactant. The order of
that reactant concentration in the rate law can be determined by observing how the reaction
rate varies as the concentration of that one reactant is varied. This method is repeated for each
reactant until all the orders are determined. At that point, the rate law can be used to find the
value of k for each trial. If the temperatures are the same for each trial, then the values of k
should be the same too. Finally, experimental data was analyzed, and reaction rates were
obtained. The order of the reaction is obtained from the rates and initial concentrations using
the initial value method. From the orders, the rate law was written, and the rate constant
calculated. It was concluded that reaction rate was concentration dependent.
2
INTRODUCTION
Determination of the rate law for the reaction is critical for both studying chemical kinetics as
well as achieving good process efficiency in chemical manufacturing industries. The primary
aim of this experiment is to conduct a series of reactions from which the rate law expression
will be determined for hydrolysis of ethyl acetate by sodium hydroxide (saponification).
Industrially, the rates of reactions need to be known to reduce the cost of producing or
manufacturing products. This can be easily explained because having a slow rate of reaction
means that more time is spend on manufacturing the product, whereas having a fast rate of
reaction, there is less time spent on manufacturing the product, hence maximizing potential
profits [1]. Effectiveness of the experiment solely depends on the reactor in which it is executed
on (design, process as well as the conditions of the reactor). All the reactions were undertaken
in a batch reactor. A batch reactor is used for small scale operations, evaluating new processes
that have not been fully developed, for the manufacture of expensive products like
pharmaceuticals and for the processes that are difficult to convert to continuous processes [2].
The reactor is charged via two holes in the top of the tank. While reaction is carried out, nothing
else is put in or taken out until the reaction is done. The tank can be easily heated or cooled by
jacket. Batch reactors allows more versatility and control. They have the advantage of high
conversions that can be obtained by leaving the reactants in the reactor for long periods of time.
Moreover, the capital costs involved in a batch reactor is often less than for corresponding
continuous processes when the desired rate of production is low. In operations where rapid
fouling or contamination of fermentation cultures is to be avoided, batch reactors are preferred
as they permit necessary cleaning and sanitation procedures. Nevertheless, a batch reactor's
operating costs are higher as it requires periodic filling, barrel emptying, and large-scale
production is challenging [3].
3
THEORY
A chemical reactor is characterized as a system properly designed to allow reactions to occur
on specified products under controlled conditions. Chemical reactors vary greatly in size and
structure for a visual observation; however, in order to derive a mathematical model for their
quantitative analysis, two key features must be considered: operation mode ie (continuous vs
discontinuous) and the mixing efficiency ie (perfect vs partial mixing) [4]. Batch reactors are
examples of "closed reactors" which, once inoculated, do not receive any additional mass or
energy inputs and do not require waste material outputs. Batch reactors can be stirred or not
stirred, but conditions in the reactor are continuously changing in any case. The mathematical
model of the ideal batch reactor consists of mass and energy balances, which provide a set of
ordinary differential equations that, in most cases, must be solved numerically [5]. According
to (Mohd Danish, 2015) batch reactors are designed to demonstrate the mechanism of a
chemical reaction in this type of reactor and the effects of the operative conditions, such as
reaction temperature, concentration, stirring rate on reaction rate in the isothermal and adiabatic
conditions. Materials are charged into a batch reactor and the reaction proceeds with time.
Batch reactor effects unsteady state operation hence control of temperature, pressure and
volume is inevitable.
Figure 1: Batch reactor service unit flow diagram (left) & laboratory scale batch reactor
The reaction being investigated is the hydrolysis of sodium hydroxide to ethyl acetate. The
ethyl acetate and hydroxide ion reaction yield ethanol and acetate ions as shown below;
CH3COOC2H5 (aq) + OH- (aq) + CH3CH2OH (aq) + CH3COO- (aq)
(1)
The progress of this reaction can be observed by measuring the reaction mixture conductivity.
Both sodium hydroxide and sodium acetate contribute conductance to the reaction solution
Although these reactants and products each contain an ion, the OH– ion has a higher ionic
mobility than the CH3COO– ion. Hydroxyl ion has a very much larger specific conductance
than acetate ion. Hence, the alkaline hydrolysis of ethyl acetate may be monitored by following
the change in the conductance of the reaction mixture with time [6]. By determination of the
conductivity and hence concentration as a function of time, order of reaction and hence the rate
constant is found. If the reaction is carried out at different temperatures, the activation energy
can also be found.
4
The method of initial rates was used to determine the rate law for the reaction in this practical.
The method of initial rates allows the values of reactants order of reaction to be found by
running the reaction multiple times under controlled conditions and measuring the rate of the
reaction in each case. The following correlations allow calculating the concentration of NaOH,
using the measured conductivity, and then the conversion. At infinite time (Assuming 100%
conversion)
c NaAc  c inEtAc
in
if c in
EtAc  c NaOH
c NaAc  c inNaOH
if c inEtAc  c inNaOH

in
in
c NaOH
 c NaOH
 c EtAc
if c inEtAc  c inNaOH , then
The following correlations allow calculating the conversion at time
   t  
t
o
o
CNaOH
 o
 CNaOH  CNaOH  CNaOH
 o   

XA 

(2)
0
t
c NaOH
 c NaOH
0
c NaOH
Where t :
(3)
Conductivity of reaction mixture at time t
o:
Conductivity of reaction mixture at time t=0
 :
Conductivity of reaction mixture at time t= 
(Assuming 100% conversion)
The conductivity (Siemens/cm) is correlated with concentration of the species and the
temperature by the following equations:
Λ AcNa = 0.091[1+ 0.0284(T-298)] cAcNa for T≥298
(4)
ΛNaOH = 0.248[1+ 0.0184(T-298)] aNaOH for T≥298
(5)
Λ0 = Λ0NaOH (assumes c0AcNa = 0)
(6)
Λ∞ = Λ∞NaOH + Λ∞AcNa
5
EXPERIMENTAL PROCEDURE
The following procedure was adopted for the success of the experiment. Sodium hydroxide
(NaOH) solution of 750 ml with 0.05 M (2g/liter) concentration was prepared then poured into
the reactor. The stirrer was switched on using the controls on the panel of the unit then its speed
was fixed to 50%, upon reaching of the stirrer speed the hot water circulator was started until
a desirable temperature of was reached then it was switched off. While waiting for the
temperature to reach the desirable point, 4.4g of ethyl acetate (MW = 88) was weighed onto an
Erlenmeyer flask so that a desired concentration of (4.4g/1000l = 0.05) would be obtained.
When the temperature reached 25°c, the ethyl acetate was poured into the reactor using the
stopper on the lid and at the same time the data acquisition was started with a sampling time of
10 seconds for a length of 240 seconds (4 mins). The reactor was then drained and washed with
distilled water to avoid contaminating the next trial and the experiment procedure was repeated
using two-case scenario; where the concentration of sodium hydroxide was maintained
constant while that of ethyl acetate was varied; then the other case where of concentration ethyl
acetate was maintained constant and that of sodium hydroxide being varied.
APPARATUS USED




1000ml Measuring Cylinder
Spatula
Mass scale
Laboratory batch scale unit (CRB/EV)
6
EXPERIMENTAL RESULTS
The results recorded show a decrease in the value of the conductivity as the reaction progresses.
Graphs show a steady, nonlinear decline in conductivity. Gradient of each conductivity-time
graph gives an approximate rate of reaction for corresponding test.
TABLE 1: Experimental results for four tests
TEST
c0NaOH
(M)
c0AcEt
(M)
RATE
(µScm-²s-1)
Conversion (XA)
%
𝐶𝑁𝑎𝑂𝐻 𝑡
(M)
1
0.05
0.03
0.0036
37.6
0.0312
2
0.05
0.05
0.0067
63
0.0185
3
0.05
0.07
0.0051
7.4
0.0463
4
0.07
0.05
0.0085
80.1
0.00594
5
0.03
0.05
0.0035
18
0.0246
GRAPH 1: Relationship between conductivity of the mixture with time, Test 1
Conductivity vs Time
Conductivity(µScm-²)
6,2
6
5,8
y = -0.0036x + 6.0547
5,6
5,4
5,2
5
0
50
100
150
Time(S)
Reaction rate = Conductivity / Time
= 0.0036 (µScm-²s-1)
7
200
250
300
GRAPH 2: Relationship between conductivity of the mixture with time, Test 2
Conductivity vs Time
7
Conductivity(µScm-²)
6,5
6
y = -0.0067x + 6.2702
5,5
5
4,5
4
0
50
100
150
Time (S)
200
250
300
Reaction rate = Conductivity / Time
=0.0067 (µScm-²s-1)
GRAPH 3: Relationship between conductivity of the mixture with time, Test 3
Conductivity vs Time
Conductivity (µScm-²s-2 )
4,5
4,4
4,3
y = -0,0051x + 5,304
4,2
4,1
4
3,9
3,8
170
190
210
230
250
Time (S)
Reaction rate = Conductivity / Time
= 0.0051 (µScm-²s-1)
8
270
290
GRAPH 4: Relationship between conductivity of the mixture with time, Test 4
Conductivity vs Time
Conductivity(µScm-²)
8,50
8,00
7,50
y = -0,0085x + 8,2205
7,00
6,50
6,00
0
50
100
150
Time(S)
200
250
300
Reaction rate = Conductivity / Time
= 0.0085 (µScm-²s-1)
GRAPH 5: Relationship between conductivity of the mixture with time, Test 5
Conductivity(µScm-²)
Conductivity vs Time
3,80
3,60
3,40
3,20
3,00
2,80
2,60
2,40
2,20
2,00
y = -0,0035x + 3,561
0
50
100
150
Time (S)
Reaction rate = Conductivity / Time
= 0.0035 (µScm-²s-1)
9
200
250
300
SAMPLE OF CALCULATIONS (Consider Test 5)
[ All time dependent variables were extracted at t = 120s ]
Rate of reaction = gradient of the line = 0.0035 (µScm-2s-1)
To determine order (𝛼) of sodium hydroxide (NaOH), choose tests 5 and 4
Rate Test 5
k[NaOH]α [AcEt]β
=
Rate Test 4
k[NaOH]α [AcEt]β
0.0035 k[0.03]α [0.05]β
=
0.0085 k[0.07]α [0.05]β
0.4118 = 0.4286β
ln 0.4118 = 𝛼ln(0.4286)
𝛼 = 1.05 ≈ 1
To determine order (β) of ethyl acetate, choose tests 1 and 2
Rate Test 1
k[NaOH]α [AcEt]β
=
Rate Test 2
k[NaOH]α [AcEt]β
0.5373 = 0.6β
0.0036 k[0.05]α [0.03]β
=
0.0067 k[0.05]α [0.05]β
ln(0.5373) = βln(0.6)
β = 1.22 ≈ 1
Test 2 was chosen to determine the value of the rate constant.
Rate Test 2 = k[NaOH]α [AcEt]β
0.0067 = k[0.05]1 [0.05]1
k = 2.68 s-1
in
AcEt ≤ cinNaOH for the first two tests
c∞NaOH = cinNaOH – cinAcEt
=0.05 - 0.05
=0M
Conductivity at infinity (˄∞ ) for Test 2 = 4.83 µScm-2s-1
˄0 − ˄t
Ct NaOH = (
) (C∞ NaOH − C0 NaOH ) + C0 NaOH
˄0 − ˄∞
=
6.45 − 5.43
(0 − 0.05) + 0.05
6.45 − 4.83
=0.0185
XA =
C0 NaOH − Ct NaOH
0.05 − 0.0185
=
= 0.63
0
C NaOH
0.05
10
DISCUSSION
In accordance with study by (Mohd Danish, 2015) on rates of inorganic compounds
hydrolysis, hydrolysis of Ethyl Acetate in the presence of Sodium Hydroxide is a prominent
irreversible 2nd order overall and 1st order with respect to each reactant. Reaction order
diminishes and become sequential rather than 2nd order when equimolecular concentrations of
both reactants are used., this conclusion is in concurrence with the outcomes we got from this
investigation as reaction order of both reactants was calculated to 1 in approximation. Gradient
(resembling reaction rates) of all graphs plotted for each test conducted are negative, this is due
to that conductivity of the reaction mixture for all test conducted decreases with time.
Decrement of conductivity among five trials, is due to that as reacting ions collide with proper
orientation, energy required to start the reaction is minimized ie activation energy (as indicated
by Collision theory) and for this particular reaction, nonpolar compounds are produced ie
ethanol and sodium acetate. Hydroxyl ion liberated during the reaction influences the peak of
conductivity as it has more conductance in comparison to other ions present in the reacting
mixture. This is emphasized by “Test 4” results ie due to high concentration of sodium
hydroxide prepared for this test, higher reaction rate (0.0085µScm-²s-1) , higher conversion
(80.1%) and the highest conductivity peak of (8.34 µScm-²s-2) was recorded.
Based on results obtained concentration of reactants is of high significance as along with other
factors such as temperature, dictates the rate of reaction. High concentration of reactants means
that there are abundant mobile reacting ions in the mixture. “Test 5 reacting mixture” was
prepared such that it had lowest concentration of hydroxyl donor ie NaOH hence the least
reaction rate (conductivity) of 0.0085µScm-²s-1 was recorded for this test. Conversion increases
with time until state of equilibrium is achieved, and as for Test 5, equilibrium state was reached
faster.
Due to the versatility of batch reactor, all five reaction tests with unique concentration levels
of reactants were conducted within the stipulated interval. The drawback encountered was that
the batch reactor limited the accuracy of the results as it initiated the errors accumulated during
the proceedings of the study. Inaccuracy of the results is depicted by abnormal trend of the
graphs plotted e.g Graph 5 and 1 representing Test 5 and 1 respectively has fluctuating trends,
which theoretically is not supposed to occur. This might have been due to accumulated
contamination of the reactor during execution of different experiments. Inaccurate chemical
preparation of reactants dilution might have also contributed to disrupt results obtained for
some of the test conducted.
11
CONCLUSION
As a conclusion, sodium hydroxide contributes stronger conductivity compared to ethyl
acetate. Thus, as the time increase, the concentration of sodium hydroxide decreases and the
conductivity decrease. At the same time, the concentration of sodium ions increases and cause
the conversion to increase.It was determined from the experiment that the reaction is of second
order overall, first order with respect to concentration of sodium hydroxide and first order with
respect to ethyl acetate. The rate constant was calculated and determined to be 2.68s −1. It can
also be seen from this experiment that rate of reaction depends on the concentration
(experimental variable); different values for the rate of reaction were obtained for varied
concentrations of the reactants. Operating temperature was the experiment control variable. In
addition, the conversion of the reaction increases with increase in ethyl acetate concentration
but decreases as the concentrations of the two reactants equal each other.
RECOMMENDATIONS
Few measures are suggested to increase the accuracy of results obtained. Concentrations of the
reactants should be accurately prepared; conductivity meter should also be well calibrated. To
reduce contamination, distilled water should be used to thoroughly clean the reactor before the
proceeding batch is fed to the reactor. The reactor should be jacketed to improve its ability to
maintain constant temperature despite environmental conditions at any instance. To improve
reactors temperature control system the ON/OFF controller can be replaced with PI or PID
controller.
12
REFERENCE
1. Denbigh KG, Turner JCR (1971) Chemical Reactor Theory, 2nd edn, Cambridge
University, Chemical Reaction Engineering, John Wiley and Sons.
2. Smith JM (1981) Chemical Engineering Kinetics, 3rd edn, McGraw-Hill, New York.
3. Walker J (1906) A Method for Determining Velocities of Saponification. Royal
Society of London. 7. Shoemaker D (2003) Experiments in Physical Chemistry.
McGraw-Hill. 8. Atkins P, de Paula J, Depaula J, Atkins PW (2006) Atkins’ Physical
Chemistry.
4. Mohd Danish, Mohammad K. Al Mesfer and Md Mamoon Rashid (2015)
, Effect of Operating Conditions on CSTR Performance, An Experimental Study,
International Journal of Engineering Research and Applications, 5(2), 74-78
5. Bond G.C. (1987), Heterogeneous Catalysis, Principles and Applications, 2nd Edition,
Oxford Clarendon Press.
6. Dane K (2007) Chemical and Biological Reaction Engineering. Spring.
13