Question

Explain the preparation of ethene gas by dehydration, giving chemical equations.

Answer 1

In dehydration reaction there is removal of water from the reactant molecule or ion. This reaction is the reverse of the hydration reaction in which there is addition of water molecules to the reactant molecule. Dehydration can be done by adding some dehydrating agent or heating the reactant.

Complete step by step answer:
In this question we have to explain the preparation of ethene gas by dehydration method. Ethene is the hydrocarbon formed from two carbon atoms (prefix eth in the name of compound is used for two carbon atoms) and there is double bond between these two carbon atoms (suffix ene is used in the name of the compound to represent double bond between carbon atoms). Chemical formula of ethene is ${C_2}{H_4}$. Sulphuric acid acts as a dehydrating agent that is this acid helps to remove water from the compound. Now we have to find the chemical compound which on removing water molecules will give ${C_2}{H_4}$ which is ethene. Ethanol is the compound which on dehydrating will give ${C_2}{H_4}$. Chemical formula of ethanol is ${C_2}{H_5}OH$. On removing water from this compound, the chemical formula of the resulting compound will be ${C_2}{H_4}$. This means ethanol will give ethene on dehydration. As stated above sulphuric acid acts as a dehydrating agent this means reaction of ethanol in presence of sulphuric acid will yield ethene. Reaction will be as follows:
${C_2}{H_5}OH\xrightarrow[{{{160}^ \circ } - {{170}^ \circ }C}]{{{H_2}S{O_4}}}{C_2}{H_4} + {H_2}O$

Note:
Temperature should be in-between ${160^ \circ } - {170^ \circ }C$ for this reaction. In place of sulphuric acid phosphoric acid can also be used as a dehydrating agent. Chemical formula of phosphoric acid is ${H_3}P{O_4}$. Acids added as dehydrating agents are not the reactants. These acids work like catalysts.