Preparing Alkene

Alkene can be prepared by
  1. dehydration of alcohol
  2. craking of alkane

Dehydration of Alcohol

When alcohol is heated, it will decompose to form alkene and water. For example, heating ethanol will produce ethene, heating propanol will produce propene, and so on. This process is called dehydration of alcohol.

Dehydration of Ethanol 
    C2H5OH → C2H4 + H2O 
Dehydration of Propanol
    C3H7OH → C3H6 + H2O

Dehydration of Alcohols Using Aluminium Oxide as Catalyst


Catalyst:
Aluminium oxide/ Porcelain chips

Dehydration of alcohols using an acid catalyst


Catalyst:
Sulphuric acid or Phosphoric acid

Temperature: 170°C

Cracking of Alkane

  1. Cracking is the name given to breaking up large hydrocarbon molecules into smaller and more useful bits.
  2. This is achieved by using high pressures and temperatures without a catalyst, or lower temperatures and pressures in the presence of a catalyst.

Example: Cracking of butane


Cracking of butane produces a mixture of methane, ethane, ethene and propene.

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