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Question

What is the bromine test used for?


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Solution

Unsaturated hydrocarbons

  • Hydrocarbons with double or triple covalent bonds between neighboring carbon atoms are said to be unsaturated hydrocarbons.
  • The term "unsaturated" denotes the possibility of adding extra hydrogen atoms to the hydrocarbon to make it saturated.
  • Alkynes and alkenes are unsaturated hydrocarbons.
Tests for Unsaturation

Bromine test used for

  • The bromine test is also known as the bromine water test.
  • It is an unsaturation test.
  • Alkene or alkyne unsaturated carbon-carbon bonds can be detected using the bromine test.
  • An organic molecule is given to a reactant, in this case, bromine, to break a double- or triple-bond.
  • This type of chemical reaction is known as an addition.

Bromine test reaction

  • When bromine is in solution, it has an orange-brownish color, but when bromine reacts with an alkene or an alkyne, the color of the solution disappears.
  • Alkanes can't react with bromine since they only have single bonds.
  • Therefore, when they are combined, there is no color change.
  • However, bromine will react with aromatic compounds like phenol.
  • Benzene is insufficiently reactive without a catalyst to undergo a bromine reaction.
  • However, this reaction can occur in the presence of a catalyst.
  • Since phenol has more reactivity than benzene, it can interact with bromine without a catalyst.
  • This is because the alcohol group contributes electron density to the delocalized benzene ring.

Reaction

  • When ethene reacts with bromine C2H4 react with bromine it can form 1,2-dibromoethane which causes decolouration.
  • The reaction is as follows:

Bromine water test - Preparation of bromine water solution and application  of bromine water solutions.


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