Alcohols Flashcards
What are the properties of alcohols?
- they contain an -OH functional group
- the general formula is CnH2n+1OH
What are the physical properties of alcohols?
- High melting points
- Soluble in polar solvents
- less volatile than their corresponding alkanes
What is volatility?
The tendency for alcohols to vapourise
Why do alcohols have these properties?
- they have a polar O-H bond due to the difference in electronegativity of oxygen and hydrogen, this makes them soluble in polar solvents whereas alkanes are non-polar
- Due to their OH group, alcohols have hydrogen bonds between them, as well as london forces
- ## Hydrogen bonds require more energy to overcome, increasing their melting point and volatility compared to alkanes which only use london forces
Draw a hydrogen bond
look at notes for the answer xx
Why are alcohols soluble ONLY in polar solvents?
- they are polar and form hydrogen bonds with polar solvents, making them more soluble
What affects the solubility of alcohols?
- as the chain length of alcohols increases, the influence of london forces increases and the influence of the OH- bond decreases. This makes them less souble so, as chain length increases, solubility decreases
What is a primary alcohol?
- The -OH group is attached to a carbon atom THAT is attached to two hydrogens and one alkyl group
Give an example of a primary alcohol and its exception
(draw both x)
- Methanol is an exception
- ethanol is a primary alcohol
What is a secondary alcohol?
- the OH group is attached to a carbon atom THAT is attached to one hydrogen and two alkyl groups
What is a tertiary alcohol?
- the OH group is attached to no hydrogen atoms and three alkyl groups
Give an example of a secondary alcohol (draw)
- propan-2-ol
Give an example of a tertiary alcohol (draw)
- 2 - methylbutan-2-ol
What reactions do alcohols undergo?
- combustion
- elimination
- oxidation
- substitution
Describe the combustion of alcohols and write an equation for the combustion of ethanol.
- Alcohols completely burn in a plentiful supply of oxygen, forming CO2 and H20
- this is an exothermic process
- C2H5OH + 3O2 = 2CO2 + 3H2O
What is the usual oxidising mixture to oxidise a primary or secondary alcohol?
- pottasium dichromate acidified with dilute sulfuric acid
What is the colour change of potassium dichromate?
- if an alcohol is oxidised, the potassium dichromate be reduced from orange to green
What can primary alcohols be oxidised to?
- aldehydes
- carboxylic acids
How do u prepare aldehydes?
- when you heat a primary alcohol with acidified potassium dichromate an aldehyde is formed
- to ensure that this not a carboxylic acid, the aldehyde is distilled out of the reaction mixture
- the potassium dichromate will turn from orange to green
GIve an example of aldehyde preparation (butan - 1 - ol)
Look at notes
Draw a distillation set up
- notes
What is the general equation for the preparation of aldehydes
- notes
How do you prepare carboxylic acids?
- Heat the primary alcohol strongly under reflux, this ensures any aldehydes formed undergo oxidation and form a carboxylic acid
- Dichromate ions go from orange to green
Give an example of this equation (butan-1-ol)
notes
Draw a diagram of reflux
What is the general equation of the reflux of secondary alcohols?
How do you prepare ketones?
- You can prepare a ketone by oxidising a secondary alcohol under reflux
- the dichromate ions turn from orange to green
write out the equation for the oxidation of propan - 2 - ol (secondary)
What occurs when you oxidise a tertiary alcohol?
- nothing, the dichromate ions remain orange
What is dehydration?
-any reaction where water is removed from a starting material
What occurs when you dehydrate an alcohol?
- it forms an alkene
- there are many products for this
What are the conditions required to dehydrate an alcohol?
- an acid catalyst
- concentrated H3PO4
- reflux
What occurs during a substitution (with halide ions) reaction with an alcohol?
- a haloalkane is formed
What are the conditions to form a haloalkane from an alcohol?
- heated under reflux with sulfuric acid
