Alkenes and alcohols

  • Created by: Andrew
  • Created on: 26-10-18 16:32


Definition: Unsaturated hydrocarbons with a C=C (carbon double bond) functional group

  • Unsaturated - Not combined with as much hydrogen as possible
  • Hydrocarbons - Molecules made from only carbon and hydrogen atoms
  • Functional group - A group of atoms in a compound that determine the nature of the reaction that the compound will undergo


  • Highly reactive (due to carbon double bond)
  • Homologous series (all have twice as many hydrogen atoms as carbon atoms)
  • Unsaturated

The four shortest alkenes in order are: Ethene, propene, butene, pentene

Methene is not possible as it would have a single carbon atom so cannot have a C=C bond

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Reactions of alkenes

Key points:

  • The functional group (C=C double bond in alkenes) determines how it will react
  • A common reaction for alkenes is addition reactions, the C=C bond opens and new atoms bond with the carbon

Some addition reactions with alkenes are:

  • Alkene + water (steam) + posphoric acid catalyst --> alcohol
  • Alkene + oxygen --> carbon monoxide + carbon (soot) + water   (combustion)
  • Alkene + hydrogen + nickel catalyst --> alkane    (this process is called hydrogenation)
  • Alkene + bromine water --> dibromoalkane    (this can be used to differenciate between alkanes and alkenes as alkanes do not react with bromine water)
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Image for addition reaction of an alkene

Image of addition reaction of alkene and another chemical

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Definition: An organic compound with a hydroxyl (OH) functional group bonded to a saturated carbon atom

  • Hydroxyl - An OH functional group
  • Saturated - Bound to as much hydrogen as possible, no double (or more) bonds

The general formula for an alcohol is: CnH2n+1OH

The four smallest alcohols are: Methanol, ethanol (the alcohol we consume), propanol, butanol

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Reactions of alcohols

  • The funtional group for alcohols is a hydroxyl (OH) group

Some reactions of alcohols:

  • Alcohol + water --> neutral solution
  • Alcohol + air (and heat) --> carbon dioxide + water       (combustion)
  • Alcohol + oxidising agent --> carboxylic acid
  • Alcohol + sodium --> hydrogen
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A common method for producing ethanol, yeast is added to a sugar solution to produce ethanol and carbon dioxide.

Ideal conditions:

  • 37°C
  • Slightly acidic
  • Anaerobic

Side note: This is how alcoholic drinks are made, the carbon dioxide produced is also what makes bread rise.

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Carboxylic acids

Definition: An organic compound with a carboxyl functional group

  • Carboxyl functional group - carbon with a double bond to oxygen and a single bond to a hydroxyl group, written as COOH
  • The general formula for a carboxylic acid: CnH2n+1COOH

The four smallest carboxylic acids in order are: methanoic acid, ethanoic acid, propanoic acid, butanoic acid

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Reactions of carboxylic acids

  • The functional group is a carboxyl (COOH) group

Some reactions are:

  • Carboxylic acid + a carbonate --> a salt + carbon dioxide + water
  • Carboxylic acid + water + acid catalyst --> ester + water
  • Carboxylic acid + water --> acidic solution
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Addition polymerisation

Definition: The joining of short chain monomers (molecules in a polymer) to produce a long chain polymer

Important: Alkenes are used as monomers in addition polymerisation because their carbon double bonds open to bond to other monomers

  • In this reaction, the polymer is the only product.
  • Naming polymers is easy, just add "poly" in front of the monomers name


  • Ethene monomers join to create poly(ethene)
  • Propene monomers join to create poly(propene)
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