Alcohols, Halogenoalkanes and Analysis

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  • Created by: helena
  • Created on: 28-05-13 17:45

Making and Using Alcohol

Hydration of Ethene 

  • H2C=CH2 (g) + H2O (g) <--> CH3CH2OH (l) 
  • H3PO catalyst, 300oC and 60 atm
  • reaction is reversible, so overall 95% of the ethene is converted

Fermentation of Sugar

  • C6H12O6 (aq) -->  CH3CH2OH (l) + CO2 (g)
  • yeast catalyst and37oC


  • alcoholic drinks, as fuel, methylated spirits( fuel in spirit burners)


  • clean burning fuel, chemical feedstock
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Properties of Alcohols

Hydrogen bonds are present. These result in

  • high melting and boiling points 
  • lower volatility

Alcohols dissolve in water due to hydrogen bonds

Solubility decreases as chain length increases because there is a longer non-polar hydrocarbon chain

In a primary alcohol the -OH group is attached to a carbon atom with one or no alkyl groups

In a secondary alcohol the -OH group is attached to a carbon atom attached to two other alkyl groups

In a tertiary alcohol the -OH group is attached to a carbon atom attached to thee other alkyl groups

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Oxidation of Alcohols

Primary and Secondary alcohols can be oxidised using an oxidising agent

oxidising agent = [o] = acidified potassium dichromate

during this reaction the colour change is orange to green

primary alcohols + [o] --> (distillation) aldehyde + water

primary alcohols + [o] --> (reflux) carboxylic acid + water 

Secondary Alcohols + [o] --> (heat) ketone + water

Tertiary alcohols are resistant to oxidation. The oxidising agent remains orange

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An ester is formed when an alcohol is warmed with a carboxylic acid in the presence of a sulfuric acid catalyst

This reaction is called esterification

The -OH group from the carboxylic acid reacts with the hydrogen on the alcohol group to form the ester and water

for example 

ethanoic acid + methanol


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General Formula: CnH2n+1X where X is a halogen atom

Contain a polar carbon-halogen bond, because the halogen atom is more electronegative

The electronegativity of the halogens decrease down the group, polarity decreases

Hydrolysis occurs when it reacts with an aqueous solution of hot hydroxide ions

Nucleophilic Substitution

heated under reflux

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Rate of Hydrolysis for Primary Halogenoalkanes

The halogenoalkane is heated with aqueous silver nitrate with ethanol added. Water in the mixture acts as the nucleophile

Chloroalkane --> white precipitate

Bromoalkane --> cream precipitate

Iodoalkane --> yellow precipitate

Two factors affect the rate of hydrolysis, polarity and bond enthalpy

Rate of reaction increases down the group

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Halogenoalkanes and the environment

F2C=CF2 (tetrafluoroethene)--> -[-CF2CF2-]- (PTFE)

PTFE is inert due to C-F bonds. It's resistant to chemical attack


Cl2C=CCl2 (chloroethene)--> -[-CCl2CCl2-]- (PVC)


  • first developed as a non-toxic refrigerant
  • They break down in the presence of UV radiation to form chlorine radicals
  • catalyst for ozone depletion
  • alternatives are HFC's and HCFC's
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Percentage Yield and atom economy

% yield = actual amount, in mol, of product *100         theoretical amount, in mol, of product 

atom economy = Mr of desired product * 100  total Mr of all products

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Infrared Spectroscopy

The amount of vibration depends on 

  • the bond strength
  • the bond length
  • the mass of each atom involved in the bond
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Mass Spectrometry

Can be used:

  • to identify unknown compounds 
  • to determine the abundance of each isotope in an element
  • to gain further information about the structure and chemical properties of molecules

When an organic compound is placed in a mass specrometer, some molecules lose an electron and are ionised. The resulting positive ion is called the molecular symbol M+ 

Excess energy from the ionisation process can be transferred to the molecular ion, making it vibrate. This causes bonds to weaken and the molecular ion can be split into pieces by fragmentation

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