In the laboratory preparation of ethyl ethanoate, the water present in the mixture is removed using ?

Analysis

The question asks for the chemical agent used to remove water (a drying agent) during the laboratory preparation of ethyl ethanoate (an ester).

Concept

The preparation of ethyl ethanoate is an esterification reaction, which involves the reaction between ethanoic acid and ethanol in the presence of a concentrated acid catalyst (usually concentrated $H_2SO_4$).

The reaction is reversible:

To shift the equilibrium to the right (to produce more ester according to Le Chatelier’s Principle), the water produced must be removed. Concentrated sulfuric acid ($H_2SO_4$) serves two purposes here:

1. It acts as a catalyst to speed up the reaction.
2. It acts as a dehydrating agent to remove the water produced, thereby driving the reaction forward.

Step-by-Step Solution

1. Identify the reaction: Esterification is a condensation reaction that produces water as a byproduct.
2. Understand the role of the reagent: In the laboratory setup, we need a substance that is highly hygroscopic (water-attracting) to absorb the water formed.
3. Evaluate the options: • A (Anhydrous $CaCl_2$): While it is a drying agent, it is not the primary reagent used during the reaction mixture preparation to drive the equilibrium. • B (Concentrated $NaCO_4$): This is not a standard chemical reagent used for this purpose. • C (Dilute $NaOH$): This would cause the hydrolysis of the ester (saponification), which is the opposite of what we want. • D (Concentrated $H_2SO_4$): This is the standard reagent added to the mixture to catalyze the reaction and dehydrate the system by absorbing the water produced.

Conclusion

Concentrated $H_2SO_4$ is the correct agent used in the reaction mixture to remove water and shift the equilibrium toward the formation of the ester.

Exam Tip: Always remember that in esterification, concentrated $H_2SO_4$ is a "double-duty" worker: it speeds up the reaction (catalyst) and pulls the water out of the way (dehydrating agent) to ensure you get a higher yield of the ester.