The hydrolysis of ethyl acetate by sodium hydroxide (equal conc.)

(Second-order reaction), Saponification of Ethyl Acetate (at Equal Concentrations)

Hydrolysis of Ethyl Acetate in the Presence of Sodium Hydroxide

Purpose of the Experiment

To determine the rate constant for a second-order reaction with equal concentrations.
To determine the half-life of a second-order reaction with equal concentrations.

Theoretical Principle:

Ethyl acetate reacts with sodium hydroxide according to the following equation:

CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH

As the reaction proceeds, the concentration of reactants decreases, while the concentration of the products (ethanol and sodium acetate) increases. The reaction between ethyl acetate and sodium hydroxide is called saponification. The rate of saponification depends on the concentration of both the ester and the base, making it a second-order reaction.

The concentration of the product (X) at any time (t) can be determined from the initial concentration (a). The concentration of sodium hydroxide can be determined using a back titration method, where an excess amount of hydrochloric acid is added to neutralize the remaining base.

The rate law of the reaction is expressed as:

For equal concentrations, the equation simplifies to:

Integrating equation (2) gives:

By substituting equation (3) and (4) in terms of volume, we get:

For second-order reactions, the half-life can be determined using:

Experimental Procedure

Prepare a 100 ml volumetric flask with a standard 0.1 N hydrochloric acid solution and another flask with 0.1 N sodium hydroxide. Titrate the sodium hydroxide solution against the standard acid to determine the exact concentration of the base.
Prepare 100 ml of 0.025 N hydrochloric acid and 100 ml of 0.05 N sodium hydroxide by appropriate dilution.
Using a pipette, transfer 50 ml of 0.05 N sodium hydroxide into a clean and dry volumetric flask. Similarly, transfer 50 ml of 0.05 N ethyl acetate (density = 0.901 g/cm³) into another flask. Seal both flasks tightly and place them in a water bath at 25°C for at least 15 minutes.
Once both solutions reach thermal equilibrium in the water bath, quickly mix the sodium hydroxide solution with the ester solution. Record the exact time of mixing as t₀ (What is the concentration of both the base and ester in the reaction mixture?).
After 5 minutes, withdraw 10 ml of the reaction mixture using a pipette, transfer it into an Erlenmeyer flask containing 100 ml of distilled water and 10 ml of precisely 0.025 N hydrochloric acid. Shake the solution well and titrate the excess acid with 0.025 N sodium hydroxide using phenolphthalein as an indicator. Record the volume of sodium hydroxide used.
Repeat step (5) at different time intervals: 10, 20, 30, 40, 50, 60, and 80 minutes.

Results and Calculations

Note:

This is an illustrative example performed in the laboratory.

Graphical Representation:

Discussion

Q: What is ethyl acetate?

A: Ethyl acetate is an organic compound that appears as a colorless liquid with a distinctive sweet smell. It is an ester formed from ethanol and acetic acid and is widely manufactured for use as a solvent.

Q: What is the reaction order?

A: The reaction is second-order because the reaction rate is directly proportional to the concentrations of both ethyl acetate and the base.

Q: How does the amount of hydroxide ions affect the experiment?

A: - When hydroxide ions are present in low quantities, their concentration changes significantly, and the reaction follows second-order kinetics.

When hydroxide ions are present in large excess, their concentration remains nearly constant, and the reaction follows first-order kinetics.

Q: What is saponification?

A: Saponification is the basic hydrolysis of an ester by sodium hydroxide (NaOH). This means the ester reacts with the base irreversibly, producing an alcohol (ethanol) and a carboxylate salt (sodium acetate).