alcohols Flashcards
What is the function group of alcohols
OH hydroxyl group
What is the general formula for the alcohols
CnH2n+1OH
What is the difference between primary, secondary and tertiary alcohols
Primary alcohols have only one carbon attached to the carbon that the OH is attached to (An exception is methanol)
Secondary alcohols have two and tertiary alcohols have three
Combustion of alcohol
C2H5OH + 3O2 -> 3CO2 + 3H2O
State and explain the trend in boiling point of the alcohols as length of carbon chain increases
Boiling points increase as chain length increases due to stronger London forces therefore more energy is required to break them
Explain how a triol is more soluble in water than of 1-ol
A triol has 3 OH groups which each form hydrogen bonds with water molecules the more hydrogen bonds formed between a molecule the greater water solubility
What type of intermolecular forces do alcohols have and why
They have hydrogen bonding because of the difference in electronegativity between the oxygen and hydrogen
Why do alcohols have a higher boiling point than alkanes with the same chain length
Alcohols form hydrogen bonds,
alkenes form London forces
hydrogen bonds are the strongest type of Intermolecular forces and need more energy to overcome
explain the trend in solubility as chain length increases of Alcohols
As Alcohols are soluble because of the Hydrogen bonds that form between OH group and water, solubility decreases as chain length increases Because the non-polarity of the CH bonds takes precedence/ OH group has less influence.
What conditions are needed to partially oxidise a primary alcohol and what is formed
Heat alcohol gently with acidified potassium dichromate and distil it out to produce an aldehyde: ethanol + [O] -> water + ethanal
How do we distil out to form an aldehyde and why
draw diagram of apparatus with condenser
condenser should shows water flow
collection of organic product
product is separated to prevent further oxidation (to carboxylic acid)
what conditions are needed to fully oxidise a primary alcohol and what is produced
Heat alcohol strongly under reflux with an excess of acidified potassium chromate to form carboxylic acid
ethanol + [O] -> water + ethanoic acid
What are the conditions needed for the oxidation of a secondary alcohol and what is produced
The alcohol is heated strongly under reflux with acidified potassium dichromate To produce a ketone
propan-2-ol + [O] -> water + propanone
What is a dehydration reaction And what is produced when you dehydrate an alcohol
A reaction where water is lost to form an organic compound, Alkene and water
How do we Dehydrate alcohols
heat alcohol under reflux in the presence of an acid catalyst to produce an alkene and water. This is an elimination reaction.
What can be observed when alcohols are oxidised
The colour changes from orange to green as dichromate ions (5) are reduced to chromium ions (3)
What are the products of an alcohol substitution reaction And how is the hydrogen halide formed
Alcohol + hydrogen halide (NaBr + H2SO4) -> haloalkane + H2O + NaHSO4
Hydrogen halide is made by reacting a salt eg NaBr with an acid eg H2SO4 in situ
Suggest why an alkene is less soluble than an alcohol
- Alkenes do not have OH group
- the oh group forms hydrogen bonds with water to dissolve it
