AbstractIn this experiment, the change of NaOH concentration and conductivity is observed.

Using the “integral method” of analysis, the reaction is found to be a second order reaction. The experimental value of the activation energy is determined as well. According to authentic theoretical sources; the values of the rate constant & activation energy were relatively inaccurate, where for example the experimental reaction rate constant was found to be 0.229 L/mol.s at 25 ºC, where the theoretical value is equal to 0.111 L/mol.s at 25 ºC. At the end of the report, discussion about the calculation was written in addition to some recommendations.

I

ContentsObjective..........................................................................................................................................1

Introduction &Theory......................................................................................................................1

Apparatus & Experimental Setup....................................................................................................3

Apparatus.................................................................................................................................3

Procedure.................................................................................................................................4

Safety consideration:.......................................................................................................................4

Experimental Data...........................................................................................................................6

Calculations.....................................................................................................................................7

Reaction Taking Place.................................................................................................................7

Concentration from Conductivity Measurements........................................................................7

Steady State Concentration......................................................................................................7

Discussion......................................................................................................................................13

Conclusion.....................................................................................................................................13

Recommendations..........................................................................................................................14

References......................................................................................................................................15

II

List of FiguresFigure 1: Chemical reactors apparatus flow diagram......................................................................3Figure 2: Concentration vs. Time at 25 ºC......................................................................................9Figure 3: Concentration vs. Time at 30 ºC......................................................................................9Figure 4: Concentration vs. Time at 35 ºC......................................................................................9Figure 5: Concentration vs. Time at 25 ºC, 30 ºC and 35 ºC.........................................................10Figure 6: 1/Concentration vs. Time at 25 ºC.................................................................................10Figure 7: 1/Concentration vs. Time at 30 ºC.................................................................................11Figure 8: 1/Concentration vs. Time at 35 ºC.................................................................................11Figure 9: ln(K) vs. temperature.....................................................................................................12

List of TablesTable 1: Experimental raw data collected.......................................................................................6Table 2: Initial and final conductivity at different temperatures.....................................................7Table 3: Sodium hydroxide concentration at different temperatures and time interval..................8

III

Objective The aim of this experiment is to determine the order, rate constant, frequency factor,

and activation energy of the reaction between sodium hydroxide and ethyl acetate.

Introduction &TheoryIn a batch reactor the reactants and the catalyst are placed in a container, are well

mixed, which is then closed to transport of matter and the reaction is allowed to proceed for a

given time. Then the mixture of un-reacted material together with the products is withdrawn.

This is an unsteady state operation where composition changes with time; however at any

instant the composition throughout the reactor is uniform.

A batch reactor can be used to find the reaction rate constant, activation energy and

order of the reaction. The use of a batch reactor for the most part eliminates the effects due to

fluid flow on the resulting reaction rates. Consequently, the data reflect the intrinsic kinetics

for the reaction being investigated.

A batch reactor can also be used to demonstrate the mechanism of a chemical reaction

and the effects of the operative conditions, such as reaction temperature, concentration, and

stirring rate on reaction rate in isothermal and adiabatic conditions. Isothermal condition

requires a water chiller or cold tap water in case of exothermic reactions.

The reaction chosen is the hydrolysis of ethyl acetate by sodium hydroxide

(saponification); this reaction can be carried out under safe conditions of temperature and

pressure, and it is well documented in the literature.

CH 3COOC 2 H5+NaOH→CH 3COONa+C2H5OH

EtAc + NaOH → NaAc + EtOH

Ethyl acetate+sodium hydroxide⇔ sodiumacetate+ethanol

As the reaction proceeds, hydroxyl ions are consumed and acetate ions are produced.

Both sodium hydroxide and sodium acetate contribute conductance to the reaction solution,

whereas ethyl acetate and ethyl alcohol do not. 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. By

1

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.

The following correlations allow calculating the concentration of NaOH, using the

measured conductivity, and then the conversion.

At infinite time (Assuming 100% conversion)

cNaAc∞ =cEtAc

in if cEtAc

in <cNaOHin

cNaAc∞ =cNaOH

in if cEtAc

in ≥cNaOHin

cNaOH∞ =cNaOH

in −cEtAcin

if cEtAcin ≤cNaOH

in, then

The following correlations allow calculating the conversion at time t:

cNaOHt =( Λt−Λ∞

Λ0− Λ∞ ) (cNaOH0 )

X A=cNaOH

0 −cNaOHt

cNaOH0

Where t : 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:

c=0.070*[1 + 0.0284(T – 294)]Cco for T 294for

ΛNaOH =0.195*[1 + 0.0184(T – 294)]CAo for T 294

Λ 0=ΛNaOH (AssumescNaAc0 =0 )

2

Λ∞=ΛNaOH∞ +ΛNaAc

∞

Apparatus & Experimental Setup

ApparatusThe reactor is provided of a base to be located on the service unit, and it is vacuum

insulated on the walls and the bottom.

Inside the reactor, a stainless steel coil provides the heat transfer surface for either

heating or cooling the reactant chemicals. If heating is being carried out, the coil connectors

are connected to the supply and return flexible tubing of the hot water circulator, which is

incorporated in the service unit. If cooling is required, the flexible tubes can be connected

with a chiller or tap water.

A turbine agitator works to provide efficient mixing and heat transfer. The agitator is

driven by an electric motor mounted on the head of the reactor, and the motor is driven by a

variable speed unit in the service bench and is connected electrically to this by plug. The

socket for the plug is on the switchboard of the service unit.

The connections in the reactor head are to house the conductivity and temperature

probes, which are supplied with the service unit. The larger of the two is for the conductivity

probe. The smaller is unscrewed by hand, the temperature probes inserted and then

retightened by hand.

Figure 1: Chemical reactors apparatus flow diagram

3

ProcedurePreparations of chemicals required for experiments (Reactants) have been done:

o 2 liters of 0.05 M Ethyl Acetate

This should be made by diluting concentrated (10 M, available in lab)

ethyl acetate as follows:

Volume of concentrate = Molwt×0.1× 1

Density=88.11×0 .05

0 .90=4 .9

ml/liter of solution.

Ethyl acetate solution required for 2 liters = 4 . 9×2=9.8 ml. Add 9.8 ml ethyl acetate

in 1.5 liter of distilled water. Shake the mixture vigorously until the two liquids have

mixed. Add further water to make up the final volume to 2 liter.

o 0.05 M Sodium Hydroxide

Mass of NaOH required for 0.05 molar NaOH solution=0.05x40=2g/liter. For

experiment 2 liter of 0.05 M NaOH 4gm is required.

This may be prepared by adding 4 g of NaOH to 1.5 liter distilled water then

making up the solution to 2 liter.

Fill the reactor with 0.5 liter of 0.05 M ethyl acetate.

Start the hot water circulator and wait till the desired temperature (250C) is reached.

Pour the 0.05 M sodium hydroxide in the reactor (use the stopper on the lid).

Start the stirrer at 50% of the speed, and at the same time, start taking the data with a

sampling time of 10 sec for 5 minutes.

Drain the reactor and repeat the experiment at 30°C and 35°C.

Safety consideration: Dissolution of sodium hydroxide is highly exothermic and resulting heat may

cause heat burn and ignite flammable. So, don’t dissolve large quantity (above

10 g) in small volume of water because solution will be highly concentrated

and will liberate high amount of heat.

Ethyl acetate is very flammable. Make sure that there is no source of ignition

near where you work. The vapor may be ignited by contact with a hot plate or

4

hot water pipe. You must wear hand gloves and safety glasses while preparing

ethyl acetate solution.

Prepare chemicals and operate the equipment in well-ventilated area.

Only used chemicals specified in the equipment’s manual and in the

concentration instructed [1].

5

Experimental DataThe following data represents the conductivity at different time intervals for a batch

reactor at using three different reactor temperatures: 25 oC, 30 oC and 35 oC.

6

Table 1: Experimental raw data collected.

Time Conductivity Time Conductivity Time Conductivityt Λ t Λ t Λs mS/cm s mS/cm s mS/cm10 4.35 10 4.58 10 4.420 4.3 20 4.45 20 4.2330 4.2 30 4.34 30 4.1240 4.18 40 4.25 40 450 4.11 50 4.15 50 3.960 4.05 60 4.07 60 3.8170 3.98 70 4 70 3.7180 3.91 80 3.91 80 3.6390 3.86 90 3.82 90 3.56100 3.81 100 3.76 100 3.48110 3.76 110 3.7 110 3.42120 3.71 120 3.63 120 3.35140 3.58 140 3.5 140 3.23160 3.51 160 3.41 160 3.14180 3.44 180 3.33 180 3.05200 3.38 200 3.25 200 2.98220 3.31 220 3.17 220 2.91240 3.25 240 3.11 240 2.85260 3.2 260 3.06 260 2.8280 3.15 280 3 280 2.75300 3.11 300 2.95 300 2.7320 3.06 320 2.91 320 2.66340 3.02 340 2.86 340 2.62360 2.98 360 2.83 360 2.59380 2.94 380 2.79 380 2.56400 2.91 400 2.75 400 2.53420 2.87 420 2.72 420 2.5440 2.84 440 2.69 440 2.47460 2.81 460 2.66 460 2.5480 2.78 480 2.63 480 2.42500 2.75 500 2.6 500 2.4520 2.73 520 2.58 520 2.38540 2.7 540 2.56 540 2.36560 2.68 560 2.53 560 2.34580 2.66 580 2.51 580 2.32600 2.64 600 2.49 600 2.31

Temperature: 25°C Temperature: 30°C Temperature: 35°C

7

Calculations

Reaction Taking PlaceSodium hydroxide + Ethyl acetate Sodium acetate + Ethyl alcohol

NaOH+CH 3CooC2 H5→CH 3COONa+C2H5OH

A + B C + D

Concentration from Conductivity MeasurementsSodium hydroxide (reactant) and sodium acetate (product) being ionic compounds

contribute conductance to the reaction solution, whereas ethyl acetate and ethyl alcohol do not. The conductivity of a sodium hydroxide solution at a given concentration and temperature, however, is not the same as that of a sodium acetate solution at the same molarity and temperature, and a relationship has been established allowing conversion to be inferred from conductivity.

1. Determining the initial and final conductivity at the different temperatures:

Λ0=0. 195 [1+0 .0184 (T−294 ) ]C A0

Λ∞=0 . 07 [1+0 .0184 (T−294 ) ]C A0

The results can be represented in the following table:

Table 2: Initial and final conductivity at different temperatures.

T = 25 °C T = 30 °C T = 35 °CΛ0 Λ0 Λ0

mS/cm mS/cm mS/cm5.2338 5.6823 6.1308

Λ∞ Λ∞ Λ∞mS/cm mS/cm mS/cm1.9488 2.1973 2.4458

Steady State ConcentrationAs the reaction proceeds sodium hydroxide concentration will be go down and

sodium acetate will start forming. Progress of reaction can be monitored by measurement of

conductivity contributed by unconsumed sodium hydroxide and formed sodium acetate after

reaction. Since conductivity changes linearly with concentration, relation between

concentration and conductivity can be derived as follows.

C A

CA 0

= Λ−Λ∞

Λ0−Λ∞ ------------ (10)

8

Where:

= Measured Conductivity (mSiemens/cm), at steady state

o = Initial conductivity, i.e conductivity of pure NaOH

= Conductivity after 100% conversion, i.e conductivity of CH3COONa

2. Calculating the concentration of sodium hydroxide using the concentration-conductivity relation at the three different temperatures:

C A

CA 0

= Λ−Λ∞

Λ0−Λ∞

C A=C A0 ( Λ−Λ∞

Λ0−Λ∞ )The results are summarized in the Table 3, for an initial concentration of 0.025 mol/L:

9

Table 3: Sodium hydroxide concentration at different temperatures and time interval.

Time Conductivity Concentration Time Conductivity Concentration Time Conductivity Concentration

t Λ CA t Λ CA t Λ CAs mS/cm mol/L s mS/cm mol/L s mS/cm mol/L10 4.35 0.018 10 4.58 0.017 10 4.4 0.0132620 4.3 0.018 20 4.45 0.016 20 4.23 0.0121030 4.2 0.017 30 4.34 0.015 30 4.12 0.0113640 4.18 0.017 40 4.25 0.015 40 4 0.0105450 4.11 0.016 50 4.15 0.014 50 3.9 0.0098760 4.05 0.016 60 4.07 0.013 60 3.81 0.0092670 3.98 0.015 70 4 0.013 70 3.71 0.0085880 3.91 0.015 80 3.91 0.012 80 3.63 0.0080390 3.86 0.015 90 3.82 0.012 90 3.56 0.00756100 3.81 0.014 100 3.76 0.011 100 3.48 0.00702110 3.76 0.014 110 3.7 0.011 110 3.42 0.00661120 3.71 0.013 120 3.63 0.010 120 3.35 0.00613140 3.58 0.012 140 3.5 0.009 140 3.23 0.00532160 3.51 0.012 160 3.41 0.009 160 3.14 0.00471180 3.44 0.011 180 3.33 0.008 180 3.05 0.00410200 3.38 0.011 200 3.25 0.008 200 2.98 0.00362220 3.31 0.010 220 3.17 0.007 220 2.91 0.00315240 3.25 0.010 240 3.11 0.007 240 2.85 0.00274260 3.2 0.010 260 3.06 0.006 260 2.8 0.00240280 3.15 0.009 280 3 0.006 280 2.75 0.00206300 3.11 0.009 300 2.95 0.005 300 2.7 0.00172320 3.06 0.008 320 2.91 0.005 320 2.66 0.00145340 3.02 0.008 340 2.86 0.005 340 2.62 0.00118360 2.98 0.008 360 2.83 0.005 360 2.59 0.00098380 2.94 0.008 380 2.79 0.004 380 2.56 0.00077400 2.91 0.007 400 2.75 0.004 400 2.53 0.00057420 2.87 0.007 420 2.72 0.004 420 2.5 0.00037440 2.84 0.007 440 2.69 0.004 440 2.47 0.00016460 2.81 0.007 460 2.66 0.003 460 2.44 -0.00004480 2.78 0.006 480 2.63 0.003 480 2.42 -0.00018500 2.75 0.006 500 2.6 0.003 500 2.4 -0.00031520 2.73 0.006 520 2.58 0.003 520 2.38 -0.00045540 2.7 0.006 540 2.56 0.003 540 2.36 -0.00058560 2.68 0.006 560 2.53 0.002 560 2.34 -0.00072580 2.66 0.005 580 2.51 0.002 580 2.32 -0.00085600 2.64 0.005 600 2.49 0.002 600 2.31 -0.00092

Temperature: 25°C Temperature: 30°C Temperature: 35°C

3. Plotting the concentration versus the time:

10

0 100 200 300 400 500 600 7000.0000.0020.0040.0060.0080.0100.0120.0140.0160.0180.020

Time(s)

Conc

entr

ation

(mol

/L)

Figure 2: Concentration vs. Time at 25 ºC

0 100 200 300 400 500 600 7000.0000.0020.0040.0060.0080.0100.0120.0140.0160.018

Time(s)

Conc

entr

ation

(mol

/L)

Figure 3: Concentration vs. Time at 30 ºC

0 100 200 300 400 500 600 700-0.002000.000000.002000.004000.006000.008000.010000.012000.014000.01600

Time(s)

Conc

entr

ation

(mol

/L)

Figure 4: Concentration vs. Time at 35 ºC

Summing the three graphs in one:

11

0 100 200 300 400 500 600 700

-0.005

0.000

0.005

0.010

0.015

0.020

concentration at 25 Cconcentration at 30 Cconcentration at 35 C

Time(s)

Conc

entr

ation

(mol

/L)

Figure 5: Concentration vs. Time at 25 ºC, 30 ºC and 35 ºC

4. Using the integral method to find the rate order of the reaction at different temperatures:

0 100 200 300 400 500 600 7000.000

20.000

40.000

60.000

80.000

100.000

120.000

140.000

160.000

180.000

200.000

f(x) = 0.229009089617741 x + 47.971105889981R² = 0.996862595673459

Time(s)

1/ C

once

ntra

tion

(mol

/L)

Figure 6: 1/Concentration vs. Time at 25 ºC

12

0 100 200 300 400 500 600 7000.000

100.000

200.000

300.000

400.000

500.000

600.000

f(x) = 0.641493646213048 x + 20.6316886332574R² = 0.957180143916457

Time(s)

1/ C

once

ntra

tion

(mol

/L)

Figure 7: 1/Concentration vs. Time at 30 ºC

0 100 200 300 400 500 600 700

-30,000.000

-25,000.000

-20,000.000

-15,000.000

-10,000.000

-5,000.000

0.000

5,000.000

10,000.000

Time(s)

1/ C

once

ntra

tion

(mol

/L)

Figure 8: 1/Concentration vs. Time at 35 ºC

The plot of the inverse of the concentration versus time determines the rate of the reaction. The plot at a temperature of 25 oC and 30 oC shows a straight positive slope, which gives it the characteristics of the second order reaction as shown in the following equation:

1Ca =kt +

1Cao

The third plot of 35 oC, showed unreasonable results, thus it was neglected in the calculation.

5. The pre-exponential factor (E/R.T) can be determine by plotting Ln(k) versus 1/T, as shown in the following equation:

13

K (T )=A⋅eE / RT

Ln[ K (T )]=Ln[ A ]− ER⋅T

k T 1/T L/mol.s K 1/K0.229 -1.474033275 298.15 0.0033540160.6415 -0.443946095 303.15 0.003298697

ln k

By plotting Ln(K) vs. the temperature(T), the slop would represent(-E/RT) and the intercept gives the pre-exponential factor(A):

3.29E-03 3.30E-03 3.31E-03 3.32E-03 3.33E-03 3.34E-03 3.35E-03 3.36E-03

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

f(x) = − 18620.7154824958 x + 60.9801524783732

[1/T]

Ln[K

]

Figure 9: ln(K) vs. temperature

Slope(m)=−18621⇒−ER

=−18621⇒E=18621⋅R=18621⋅8 .314=154814 . 994Jmol

Intercept (c )=60 . 98=Ln[ A ]⇒ A=3. 0428⋅1026

14

DiscussionThrough this experiment, the reaction between sodium hydroxide and ethyl acetate

was analyzed in order to improve understanding and gain hands-on experience in reaction engineering in general and batch reactors in specific.

Both ethyl acetate and ethyl alcohol are none conductive. On the other hand, sodium hydroxide and sodium acetate are conductive, sodium hydroxide is a stronger ionic compound than sodium acetate and as a result, it has higher conductivity. From these relations, the decrease in conductivity that occur as the reaction proceeds also indicate a decrease in sodium hydroxide concentration and an increment in sodium acetate concentration.

Since sodium hydroxide is being consumed over time, its concentration decline with time as can be observed in Figure 2, Figure 3 and Figure 4. After that, Figure 5 was generated in such it combines the concentration vs. time for the three temperatures of study. Figure 6, clearly indicate that the reaction is accelerated with higher temperature; that is the reaction rate increases with increasing temperature, where higher conversion rates are achieved at equal time intervals.

From Figure 6 and Figure 7, using the integral method we can conclude that the overall reaction rate is second order. Nevertheless, the experiment showed inaccurate results at 35 oC, as a result Figure 8 and its data were neglected in calculations. Furthermore, the calculated reaction rate constant and activation energy did not match for any of the used temperatures; this is mainly due to the lack of accuracy in reporting the conductivity probe measurements.

In Figure 9, the natural logarithm of the reaction rate constant was drawn against the reciprocal of temperature. The obtained line clarify the inverse proportional relationship between ln(k) and (1/T), which confirm that increasing the reaction temperature results in an increase in the reaction rate constant.

The error % that resulted at the end of the calculations was found to be relatively high. This is a result of human error factor and inaccurate temperature control.

ConclusionThe following points were the main conclusions from this experiment:

Sodium hydroxide reacts with ethyl acetate to form sodium acetate and ethyl alcohol; as a result, the concentration of sodium hydroxide was reported to decrease with time.

Sodium hydroxide has higher conductivity that any present chemical in the system, hence to find the concentration change with time, conductivity was the measured parameter.

15

It was noted that the concentration-time curve slope change with time, where the curve becomes less steep at the final stage, due to the decrease in reagents concentrations.

The reaction rate increases with increasing temperature, hence higher conversions are achieved for higher temperatures at equal time intervals.

The reaction rate was found to be second order, which confirms literature studies on the reaction.

ln k and 1/T are inversely proportional, since the reaction rate constant increases with increasing temperature.

Batch reactors are used to determine the rate law and activation energy, by measuring concentration as function of time. And then a procedure of calculations steps is followed to find, valuable reaction parameters.

High error percentage was reported when comparing literature reaction rate constant values with those obtained from the experiment. Sources of such error are:

Human factor. Imprecise temperature control.

RecommendationsIn order to, obtain accurate results and save effort. We recommend to, link the

conductivity probe with a PC computer that reads and save data continuously with higher accuracy and precision. Furthermore, to stay within a small temperature range, we recommend improving the reactor temperature control system, by replacing the ON/OFF controller with PI or PID controller.

16

References[1] M.H. Arshad, Manual: Chemical Engineering Laboratory III Reaction Engineering and Process control Lab, in: Q. University, C.o. Engineering, D.o.C. Engineering (Eds.), Qatar University, Doha, 2012.

17