Change in concentration of ethyl acetate for hydrolysis with NaOH. Effects on the rate of reaction and the specific rate constant


Internship Report, 2016

22 Pages, Grade: A


Excerpt

Research Question:

To what extent does changing concentration of ethyl acetate from 2.5×10-3 V/V to 5×10-3 V/V affect the rate of reaction and the specific rate constant of hydrolysis of ethyl acetate (ethyl ethanoate) with 0.05M sodium hydroxide (NaOH) at constant temperature of 23ºC?

Introduction:

During our classes on Organic Chemistry we learnt about hydrolysis of an ester. I wondered if this chemical breakdown of a compound could happen in a reaction with something other than water. After some research, I came to know that this process could occur by reacting an alkali instead of water. I wanted to link this, to the chapter Kinetics that we just finished. For the internal assessment, I thought of checking for the dependency of concentration on such a reaction. So, I decided to find out how fast would the reaction take place if I changed the concentration of ethyl acetate from 2.5×10-3 V/V to 5×10-3 V/V.

I want to be a scientist who develops performance devices and enhanced models that stimulate and better the chemical reacting system’s functional parameters. This concept of reaction rate, as told to me by my father, has paramount importance in the profession I yearn to be in. Although I know that increasing the concentration would increase the rate of reaction but I don’t know to what extent or by how much will it increase. In our classes we were taught about this relation, but I wanted to check for myself if it actually holds true.

I thus wished to carry out an experiment to check that what we learnt in our class theoretically, is practically observed too. So the aim of my experiment is to find out to what extent does the rate of reaction change while I change the concentration, at a particular temperature. I was also interested in finding out if there would be any consequent impact on the specific rate constant.

Background Knowledge:

A chemical reaction takes place when bonds of some molecules break and for some molecules bonds are formed. During this process some molecules undergo a change in their identity. However, according to the rules of chemistry, the total mass remains the same during a chemical reaction. Chemical kinetics is the study of rate of reactions, rate constants, formations of intermediates of chemical reactions, and its effect on variables. There are basically four types of reactions, namely, zero order reaction, first order reaction, second order reaction and third order reaction. Since this reaction of ethyl acetate with sodium hydroxide is a second order reaction[1], I shall be focusing on second order reactions. As second order reaction is such a reaction that depends on the concentration of either a second order reactant or on the concentrations of both first order reactants. The following rate equations describe the rates of the second order chemical reaction A + B ➔ C +D

illustration not visible in this excerpt[2]

The powers to which the concentrations of the reactants are raised are called the order of reaction.

The square brackets represent the concentration. Since power of [A] is 1 and the power of [B] is 1 thus the overall power becomes 2. Thus, in both the order is 2.

Since the concentration is directly proportional to the rate of reaction, k is the proportionality constant that represents the specific rate constant. Using the Arrhenius equation, [illustration not visible in this excerpt] [3]one can show the impact of the temperature and the concentration of the reactant on the rate constant and further on the rate of reaction. k is the measure of the reaction rate, which means that the greater the value of the k, greater will be the reaction rate. For this reason, it is also called the velocity constant.

The rate of reaction at a very basic level is how fast the reaction occurs. It can be a very long and time taking reaction like the rusting of iron or it can be a very fast reaction as that of potassium in air. Formally, it is the rate at which the reactants disappear and the products appear.

Using the postulates of collision theory, I can explain the factors that effect the rate of reaction:

1) Increase in temperature will increase the average kinetic energy of the particles thus there will be an increase in the frequency of the collisions and more effective collisions will take place. Therefore, there will be an increase in the rate of the reaction.
2) With an increase in the concentration there will be more number of particles in a fixed volume and therefore the number of collisions will increase and the rate of reaction will also increase.
3) Dividing a larger particle into smaller parts will increase the total surface area and hence the probability of collisions will increase and therefore the rate of reaction will increase.
4)With an increase in the pressure applied on a gas, the concentration of the particles would effectively increase and would move faster. This would increase the number of collisions and the rate of reaction would increase.
5) With an addition of catalysts, an alternative path will be provided with a lower activation energy, therefore more number of particles will have a kinetic energy which is greater than the activation energy. This means that there will be more effective and frequent collisions which in turn would increase the rate of reaction.

The rate of reaction of the hydrolysis of ethyl acetate with sodium hydroxide is given by:

illustration not visible in this excerpt

In Organic Chemistry, esters can be defined as the chemical compounds that are derived from an acid where a hydroxyl group is replaced by an alkoxy group. The hydrolysis of an ester such as ethyl acetate by an alkali such sodium hydroxide is given by the following equation:

illustration not visible in this excerpt

where [illustration not visible in this excerpt]is ethyl acetate, NaOH is sodium hydroxide, [illustration not visible in this excerpt]is sodium acetate and C2H5OH ethanol.

Research methodology

Hypothesis:

Since, as stated above, the rate of reaction is directly proportional to the concentration, therefore I hypothesized that both specific rate constant and the rate of reaction would double with the concentration of ethyl acetate doubling from 2.5×10-3 V/V to 5×10-3 V/V. This is because there will be more number particles in a fixed volume of 400ml of 0.05M NaOH solution, which is why each particle will be closer to the other and thus more frequent and effective collisions will take place which will increase the rate of reaction. I believe that the specific rate constant will too increase with concentration.

Apparatus:

1. 1 x 500 ml conical flask
2. 6 x 250ml conical flasks
3. 2 x 2 Liter jug
4. 1 x 25 ml measuring cylinder
5. 1 x 100 ml measuring cylinder
6. 1 x 500 ml measuring cylinder
7. 1 x 10 ml micro pipette
8. 1 x 50ml graduated pipette
9. 1 x 5 ml measuring cylinder
10. 1 x Stop watch
11. 1 x Stirring rod
12. 1 x Gloves
13. 1 x Safety goggles
14. 1 x Lab spoon
15. 1 x 50 ml burette
16. 1 x Burette stand
17. 1 x Funnel
18. 1 x Watch glass
19. 1 x White board marker
20. 1 x Electronic micro weighing scale

Chemicals Required

1. Sodium Hydroxide - 5grams
2. Ethyl Acetate - 5ml
3. Hydrochloric acid(12M) - 10ml
4. Distilled water - 4liters
5. Phenolphthalein - 1 bottle

Safety precautions and methods of disposal:

The chemicals used in the experiment may cause irritation to the skin therefore contact must be avoided with the solutions and the experiment must be conducted with utmost care. Also the Hydrochloric acid (HCl) used was concentrated therefore one must be cautious while using it. Therefore, it is advised to wear gloves and safety goggles while doing so. Phenolphthalein and Ethyl Acetate are flammable and are considered carcinogenic, therefore they ought to be kept away from flames. Inhalation of these chemicals must also be prevented. All the solutions must be collected in inorganic waste container and should be dumped accordingly.

illustration not visible in this excerpt

Fig1: Experiment apparatus and chemicals

Choosing and Controlling the Variables:

Since I am finding out the exact relationship between the concentration of ethyl acetate and the rate of reaction, I took the concentration of ethyl acetate as the independent variable. As per my hypothesis an increase in concentration increases both the reaction rate and the rate constant, therefore the dependent variable for this experiment are the rate of reaction and the rate constant. My controlled variables will be the concentration of sodium hydroxide (NaOH), and the concentration of Hydrochloric acid (HCl). I controlled the concentration of sodium hydroxide and hydrochloric acid by forming a solution of 0.05 molarity for both of them and using it for all trials.

Preparation of 2 liters of 0.05M HCl:

To make 2 liters of 0.05M HCl, I used the equation[illustration not visible in this excerpt]The molarity of hydrochloric acid at the lab was 12M, but I wanted to make 2 liters of 0.05M hydrochloric acid, thus:

illustration not visible in this excerpt

[...]


1 Kapoor, K. L. A Textbook of Physical Chemistry;McMillan: New Delhi, India, 2004; Vol. 5, p. 116.

2 "Second-Order Reactions." Chemwiki. N.p., 02 Oct. 2013. Web. 28 Nov. 2015.

3 Lower, Stephan. "Collision and Activation." Chem1. N.p., 2009. Web. 29 Nov. 2015. <http://www.chem1.com/acad/webtext/dynamics/dynamics-3.html>.

Excerpt out of 22 pages

Details

Title
Change in concentration of ethyl acetate for hydrolysis with NaOH. Effects on the rate of reaction and the specific rate constant
Course
IB Chem HL
Grade
A
Author
Year
2016
Pages
22
Catalog Number
V344986
ISBN (eBook)
9783668352520
File size
2060 KB
Language
English
Notes
Research into and study of the effect of changing concentration of ethyl acetate on the rate of reaction and the specific rate constant of hydrolysis of ethyl acetate at 23ºC.
Tags
change, naoh, effects
Quote paper
Sumaanyu Maheshwari (Author), 2016, Change in concentration of ethyl acetate for hydrolysis with NaOH. Effects on the rate of reaction and the specific rate constant, Munich, GRIN Verlag, https://www.grin.com/document/344986

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