Equilibrium Constant in Esterification Reaction

Viha Ancillia Bintusi Saktia, Imroatuz Zakiyahb, and Fika Fajariyahc.

aViha Ancillia Bintusi Sakti (10319409), Department of Chemistry, University of SurabayabImroatuz Zakiyah (103194005), Department of Chemistry, University of Surabaya

cFika Fajariyah (103194006), Department of Chemistry, University of Surabaya* Corresponding author, email: vancillia_92@yahoo.co.id

Abstract. We have done the experiment about “Equilibrium Constant”. The objectives to knowing equilibrium constant of a reaction and concerning that equilibrium constant is independent to concentration in initial reaction by this experiment. The method that used is titration. For make esterification reaction, first Provide 3 Erlenmeyer, pouring HCl 2N, C2H5OH, and CH3COOH by using different composition, closed all the Erlenmeyer using aluminum foils, saved it ± 1 weak, and then titrated by NaOH using PP indicator. Compered the result with Blanco solution by put 5mL of HCl 2N into Erlenmeyer flask, then titrated by NaOH using PP indicator. From this experiment got the average value of the equilibrium constant Kc is 10.46 x 10-2 mole/L, while the theoretical value for the equilibrium constant Kc = 0042 mole/L. It happen because the material used for the experimental solution was less time when let done in process, solution of this in the cupboard which the unknown temperature, beside in the outside temperature is irregular, and we difficult, to determine the end point of titration.

Keywords: Equilibrium Constant, Esterification.

INTRODUCTION

The most of the reactions that there is an

equilibrium reaction. A system is said to be in

balance if the two opposing processes occur at the

same rate or in other words no change in the

equilibrium system. The objectives of this

experiment to knowing equilibrium constant of a

reaction and concerning that equilibrium constant

is independent to concentration in initial reaction

by this experiment. In general equation for

equilibrium or reaction back and forth can be

expressed:

aA + bB ↔ cC + dD

Where a, b, c, and d are the stoichiometric

coefficients A, B, C, and D. equilibrium constant

(Kc) for reaaksi at a certain temperature can be

expressed by;

Kc =

Measurements A, B, C, and D in the system

equilibrium state have a lot of ways. This

principle will be considered when measuring the

concentration has to be pursued by methods that

do not disturb the equilibrium, which causes a

shift reaction and the concentration to be

measured to be changed. The means of

Esterification is a reaction that produces ester. It

forms from the reaction between the alcohol

(alkoksi alkane) and carboxylic acid. Ester is one

kind of derivate hydrocarbon from carboxylic

acid. The theory value of Kc in esterification is

4.2 x 10-2. The variable that influences in the

esterification reaction are:

1. Temperature. It cause by the properties of

reaction is exothermic and the temperature in

influences the value of reaction speed

constant.

2. Comparison of reactant substances. It caused

by one of the reactant should made excesses in

the forming of ester product.

3. Stirring. If we stir in the mixturing it can make

the reactant molecule is always collide so

reaction can occur optimally.

4. Catalyst. Esterification reaction run slowly, so

it needed catalyst in

In this experiment will be carried out

determination of the equilibrium constant of

acetic acid and ethanol with the titration method.

EXPERIMENTAL SECTION

Materials

The material that used on this experiment is:

NaOH 2N, PP indicator, Ethanol absolute, HCl

2N, and CH3COOH. .

Instrumentation

The instrument that used on this experiment is:

Biuret, Erlenmeyer flask, Aluminum foils,

Pipette, Graduated Cylinder (10mL), Backer

Glass (100mL), Stative, Clamp, and Funnel.

PROCEDURE

Blanco solution

Put 5mL of HCl 2N into Erlenmeyer flask, then

titrated by NaOH using PP indicator.

Esterification process

Provide 3 Erlenmeyer, for the first Erlenmeyer

pouring 5 mL HCl 2N, 1 mL C2H5OH, 4 mL

CH3COOH. The second Erlenmeyer the first

Erlenmeyer pouring 5 mL HCl 2N, 2 mL

C2H5OH, 3 mL CH3COOH. The third Erlenmeyer

pouring 5 mL HCl 2N, 3 mL C2H5OH, 2 mL

CH3COOH. The forth Erlenmeyer pouring 5 mL

HCl 2N, 4 mL C2H5OH, 1 mL CH3COOH.

Closed all the Erlenmeyer using aluminum foils,

saved it ± 1 weak, and then titrated by NaOH

using PP indicator.

RESULTS AND DISCUSSION

Blanco solution

In experiments to determine the

equilibrium constant is used to titrate. The way it

used to see if the solution has reached equilibrium

is kept absolutely perfect or just perfect. This

reaction called esterification reaction it

reversibly, as well notice that this value does not

depend on the initial concentration, except the

change of temperature.

We make Blanco Solution as comparison

to get reminder mole so that we can determine

equilibrium constants. The Blanco solution made

from 5mL HCl 2N and 3 drops PP Indicator

(colorless), that titrated by 4.9 mL NaOH 2N. So,

we get equivalent of H+ = OH- is 9.8 x 10-3 mole

and the color become pink. The reaction that

occurs in Blanco solution is:

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

Esterification process

The Observation solution of Ethanol and

Acetic Acid with the saved in 4 different volume

Erlenmeyer is covered by aluminum foil to

Prevent the vaporization of ethanol and storage

This is for also keeping room temperatures

include Because this reaction is exothermal

reaction and the temperature can influences value

is of equilibrium. And we make it without stirring

as if done Stirring will increase the frequency of

collisions between reactant molecules of a

substance that reacts with a substance that

accelerates the reaction and the reaction occurs

perfectly. It saved during 4 days to make

Esterification reaction between ethanol and acetic

acid to produce the equilibrium state of reactant

and products. The entire rest flask is added by 5

mL of HCl as catalyst, it does not involve in the

reaction at over all. Catalyst, Esterification

reaction runs slowly, so it needed catalyst in this

experiment will be carried out determination of

the equilibrium constant of acetic acid and

ethanol with the titration method. Catalyst and

also serves to reduce the activation energy in a

reaction that at a certain temperature the reaction

rate constant price increases. (Mc Ketta, 1978).

The reaction:

CH3COOH(aq) + C2H5OH(aq) ↔ CH3COOC2H5(aq)

+ H2O(l)

4 days later, each of the Erlenmeyer flask

is add by 3 drops of indicator PP. Function of the

addition of PP about 3-5 drops of indicator which

has a function for the formation of color during

titration. Then we titrated with NaOH 2 M. And

we need the volume of NaOH is 36.5 mL 25.8

mL, 16.7 mL and 10.1 mL. And there are changes

of color from colorless become pink. During the

titration, the smell of solution is like a balloon. It

indicates that the solution contains ester

(esterification). As well, the Erlenmeyer flask

becomes warm. It signals the existence of ester

too.

The reaction:

CH3COOC2H5(aq) + NaOH(aq) → CH3COONa(aq) +

C2H5OH(aq)

We get the value of Kc in Erlenmeyer flask

1,2,3,4 is 9.08 x 10-2, 10.26 x 10-2, 11.64 x 10-2,

10.856 x 10-2, and the average Kc is 10.46 x 10-2.

While the theoretically of Kc is about 4.2 x 10-2.

Fig.1. The value of Kc in Every Erlenmeyer.

The difference of the theoretical equilibrium

value constant with this experiment material

should be left in place about a week but only let it

for 4 days. Because other than that It is after we

make-the solution, we save our solution because

the material used for the experimental solution

was less time when let done in process. Solution

of this in the cupboard which the unknown

temperature, beside in the outside temperature is

irregular. And we difficult, to determine the end

point of titration. This could affect the experiment

when doing titration in solution. So results are

still not in accordance with the theoretical values

are appreciating Kc = 0.042 mole/L.

CONCLUSION

Based on the experiment that will be

done, from the above data, it was concluded that

the average value of the equilibrium constant Kc

experimentally for the average is 10.46 x 10-2

mole/L. While the theoretical value for the

equilibrium constant Kc = 0042 mole/L. and the

equilibrium constant does not depend on the

initial concentration of the reaction.

.

ACKNOWLEDGMENTS

We gratefully acknowledge Mrs. Dian

Herdyansyah as the lecture of Physical Chemistry

II, assistance of laboratories, my parents, and

other friends, because of support and the

guidance so the experiment can be done greatly.

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