Question

In conversion from ethanol to ethene, concentrated sulphuric acid is used as:

Answer 1

Hint: We know that ethanol can be converted to ethene by dehydration of ethanol. In dehydration an ethanol is heating at high temperature in the presence of concentrated sulphuric acid. The phosphoric acid can also be used instead of sulphuric acid.

Complete answer:
Ethanol is an organic compound with $C_2{H}_{5}OH$.It has a higher boiling point than ethane or another hydrocarbon such as alkane, alkyne with the same number of carbon atoms. Ethanol can directly convert to ethene by heating the ethanol in the presence of concentrated sulphuric acid. Ethanol removed water molecules from it. This process is called dehydration. Mechanism of the reaction is, the mechanism of the acid dehydration has three steps. First step is the protonation of the oxygen atom of the $-OH$ group. Second step is the removal of water molecules to form carbonium anions and the last step is the deprotonation to form carbon-carbon double bonds.
The reaction of dehydration is, $$C{H}_{3}C{H}_{2}OH+\stackrel{Conc.H_{2}S{O}_4}{\to }C{H}_2=C{H}_2+H_{2}O$$
During the conversion of ethanol into ethene in the presence of con. Sulphuric acid, a molecule of water is lost. In this reaction, conc. Sulphuric acid acts as a dehydrating agent. At $$170{}^{\circ }C$$ ethanol can be dehydrated to give ethene by heating it with an excess of concentrated sulphuric acid. This reaction is called hydration of ethane.

Note:
Remember that the following condition is required for acid dehydration is high temperature and the presence of concentrated sulphuric acid. The sulphuric acid is not mentioned in the reaction as it acts as catalyst. Role of the catalyst provides the surface area and increases the rate of reaction.