A student wished to prepare ethylene gas by dehydration of ethanol at 140°C

using sulfuric acid as the dehydrating agent. A low-boiling liquid was obtained
instead of ethylene. What was the liquid, and how might the reaction conditions
be changed to give ethylene?
Please explain

duplicate. Answered below.

To understand why a low-boiling liquid was obtained instead of ethylene, we need to examine the reaction taking place during the dehydration of ethanol.

The reaction between ethanol and sulfuric acid proceeds via an elimination reaction, where water is removed from the ethanol molecule to form ethylene. The chemical equation for this reaction is:

C2H5OH (ethanol) → C2H4 (ethylene) + H2O (water)

However, if the reaction conditions are not favorable, a side reaction known as ether formation can occur. The reaction between ethanol and sulfuric acid can also lead to the formation of diethyl ether, which is a low-boiling liquid. The chemical equation for this side reaction is:

2 C2H5OH (ethanol) → C2H5OC2H5 (diethyl ether) + H2O (water)

To obtain ethylene instead of diethyl ether, we need to modify the reaction conditions. Here are a few changes that can be made:

1. Increase the temperature: Raise the temperature of the reaction to favor the elimination reaction leading to ethylene formation. Ethylene is typically produced at higher temperatures, around 300-400°C.

2. Use a different dehydrating agent: Sulfuric acid has a tendency to promote side reactions, such as ether formation. Choosing a different dehydrating agent, such as phosphoric acid, may help to selectively favor the formation of ethylene.

3. Remove water from the reaction mixture: When water is present in large amounts, it can hinder the formation of ethylene. Using a drying agent, such as calcium chloride, to remove water from the reaction mixture can improve the yield of ethylene.

4. Use an inert atmosphere: Ethylene is highly reactive and can react with atmospheric oxygen. Performing the reaction under an inert atmosphere, such as nitrogen or argon, can prevent the oxidation of ethylene and enhance its production.

By modifying the reaction conditions as suggested above, the desired product, ethylene, can be obtained in higher yields.