How is ethene prepared by:

(a) dehydrohalogenation reaction?

(b) dehydration reaction?

Give equations and name the products formed.

(a) Dehydrohalogenation involves elimination of hydrogen halide.

$\underset{\text{ Bromo ethane [ethyl bromide]}}{\text{C}$2\text{H}5\text{Br}} + \underset{\text{alcoholic, hot and conc.}}{\text{KOH}} \longrightarrow \underset{\text{ethene [ethylene]}}{\text{C}2\text{H}4} + \underset{\text{ Potassium bromide}}{\text{KBr}} + \text{H}_2\text{O}

The products formed are ethene, potassium bromide and water.

(b) Dehydration involves elimination of elements of water from alcohol. Conc. sulphuric acid act as dehydrating agent.

$\underset{\text{ ethyl alcohol}}{\text{C}$2\text{H}5\text{OH}} \xrightarrow[170\degree\text{C}]{\text{Conc. H}2\text{SO}4\text{[excess]}} \underset{ \text{ethene}}{\text{C}2\text{H}4} + \text{H}_2\text{O}\

The products formed are ethene and water.