Reaction rate and rate constant of the hydrolysis of ethyl acetate with PDF

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In this hydrolysis of ethyl acetate with sodium hydroxide hydrochloric acid was used as catalyst to accelerate the reaction mixture. 1ml and 2ml of ethyl

Reaction rate and rate constant of the hydrolysis of ethyl acetate with

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AMERICAN JOURNAL OF SCIENTIFIC AND INDUSTRIAL RESEARCH 201D6ŃLHQŃH +Xǃ OPPSCCRRRBVŃLOXNBRUJC$-6H5

ISSN: 2153-649X, doi:10.5251/ajsir.2015.6.1.1.4

1 Reaction rate and rate constant of the hydrolysis of ethyl acetate with sodium hydroxide Ikhazuangbe, Prosper Monday Ohien and Oni, Aisosa Babalola

Madonna university, Faculty of Engineering

Chemical Engineering Department, P.m.b 302

Enugu, Nigeria

ABSTRACT

Hydrolysis is a chemical decomposition involving breaking of a bond and the addition of elements of water. In this hydrolysis of ester (ethyl acetate) with an alkali (sodium hydroxide), HCl was used as catalyst to accelerate it. 1ml and 2ml of ethyl acetate was injected separately into the

500ml reactor vessels which contains 0.05N of NaOH and thoroughly mixed. At regular time

interval, 0, 10, 20, 30, 40, and 90 minutes, 25ml of each of the samples were withdrawn into a

250ml conical flask containing 0.05N HCl, and titrated against 0.05N NaOH solution using

phenolphthalein as indicator. From the titre values, the hydrolysis involving the 1ml ethyl acetate

was faster than that of the 2ml ethyl acetate, indicating that the higher the concentration the faster

the rate of reaction. The rate constant after evaluation from the graphs was approximately

0.003min-1cm-3 for the 1ml and 2ml ethyl acetate, signifying that while the rate of reaction is

concentration dpendent, the rate constant is not dependent on concentration Key words: Alkali, concentration, ester, hydrolysis and reactor

INTRODUCTION

Chemical reaction takes place when a detectable number of molecules of one or more species have lost their identity and assumed a new form by a change in the kind or number of atoms in the compound and by a change in structure or configuration of these atoms. In this classical approach to chemical change, it is assumed that the total mass is neither created nor destroyed when a chemical reaction occurs. Chemical kinetics is the part of physical chemistry that studies reaction rates. The reaction rate for a reactant or product in a particular reaction is intuitively defined as how fast a reaction takes place. For example, oxidation of iron under the atmosphere is a slow reaction which can take years, but the combustion of butane in a fire is a reaction that takes place in seconds. Rate of reaction: The rate of reaction is defined as the change in the number of molecules of reacting species per unit volume per unit time. It is also defined to be proportional to the concentration of reacting species raised to a certain power called the order of reaction. It is usually taken as the rate at which the reactant disappear or the rate at which the is disappearing is proportional to its concentration at any instance,

I.e. rate (r) ߙ

Where k = rate constant

The concept of rate of reaction is very important in evaluating chemical reacting systems. It is the core factor in the development of performance models to stimulate reactor functional parameters.

Factors which determine rate of reaction

a. Availability of reactants and its surface area.

The greater the surface area of a solid, the

greater the rate of reaction. b. Concentration: increase in concentration increase the rate of reaction c. Pressure: increase in pressure results in an increase in the rate of reaction, if the reactants and products are gaseous d. Catalyst: The presences of a catalyst generally increase the rate of reaction. There are however, negative catalysts that lower the rate of reactions.

Am. J. Sci. Ind. Res., 2015, 6(1): 1-4

2 e. Temperature: increase in temperature increase rate of reaction Rate constant: Rate constant, K quantifies the speed of a chemical reaction. For a chemical reaction where substance A and B are reacting to produce C, the reaction rate has the form:

Reaction: A + B C

r = K[A]m[B]n Where K is the rate constant that depends on temperature A is the concentration of substance A in moles per volume of solution assuming the reaction is taking place throughout the volume of the solution. Rate constant is the rate of reaction when the concentration of each reaction is taken as unity. That is why it is also known as specific reaction rate. It is a measure of the rate of reaction, so the greater the value of the rate constant, the faster the reaction. Each reaction has a definite value of the rate constant at a particular temperature and the value of the rate constant for the same reaction changes with temperature and the values do not depend upon the concentration of reaction but depend upon order of reaction.

Hydrolysis of an ester such as acetate in

presence of a mineral acid: Hydrolysis is a chemical decomposition involving breaking of a bond and the addition of elements of water. The use of an acid catalyst accelerates the hydrolysis. The reaction rate is expressed in terms of chemical composition of the reacting species. i. The hydrolysis of an ester such as ethyl acetate in the presence of a mineral acid gives acetic acid and ethyl alcohol. CH3COOC2H5 + H2O CH3COOH + C2H5OH Ethyl acetate acetic acid ethyl alcohol Therefore, the kinetics of the reaction can be studied by taking a known quantity of ethyl acetate and mixing it with a relatively large quantity of HCl. An aliquot of the reaction mixture is withdrawn at different intervals of time and titrated against a standard alkali. Obviously, as the reaction proceeds, the value of alkali required to neutralize the acid (HCl present as catalyst + CH3COOH produced by hydrolysis of the ester) progressively increases. The fact that this is a first order reaction is established by substituting the results in the first order rate expression; quotesdbs_dbs20.pdfusesText_26

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