Chapter 14 - Alcohols
No description yet. This curated deck is ready for daily study.
Card preview (24)
What are the properties of alcohols compared to those of alkanes with the same carbon chain?
• less volatile • higher melting points • greater water solubility
Why do the boiling points of alkanes increase faster than the boiling points of alcohols?
As chain length increases, the contribution of the -OH group (hydrogen bonding) decreases and the alcohols resemble the alkanes more closely
Why is alcohol soluble in water?
As it can form hydrogen bonds with water and the polar -OH Alkanes are non-polar and doesn’t form hydrogen bonds
What is the trend of solubility as alcohol chain length increases?
Influence of the -OH group becomes relatively smaller and the solubility of longer chain alcohols becomes more like that of hydrocarbons so solubility decreases
How are alcohols classified as primary, secondary…?
Depends on the number of hydrogen atoms and alkyl groups attached to the carbon atom that contains the alcohol functional group
Why are alcohols more likely to undergo complete combustion?
As the alcohol contains an extra oxygen
What are the uses of methanol?
Highly toxic: - petrol additive (improves combustion of unleaded petrol) - solvent - raw materials (used as feedstock for important industrial processes) - fuel
What are the uses of ethanol?
• alcoholic drinks • solvent (industrial alcohol/methylated spirits) • biofuel (petrol substitute with limited oil reserves)
What does carbon neutral mean? Example?
It releases the same amount of CO2 when it is burned as was taken in from the atmosphere when the plants grew and photosynthesised Ex: using ethanol as fuel
What is the shape and angle of methanol around the C-O-H?
Non-linear 104.5 °C
What is dehydration?
Any reaction in which a water molecule is removed from the starting material
What type of reaction is the dehydration of alcohol?
Elimination reaction
What is the reaction of the dehydration of alcohols?
An alcohol is heated under reflux in the presence of an acid catalyst (concentrated sulfuric/phosphoric acid) and the product is an alkene and water
What is a substitution reaction of alcohols?
Alcohols reacting with hydrogen halides to form haloalkanes
How does the substitution reaction of alcohols work? What is the equation?
The alcohol is heated under reflux with sulfuric acid and a sodium halide to form a hydrogen halide The sodium halide reacts with the alcohol to produce the haloalkane CH3CHOHCH3 + NaBr + H2SO4 -> CH3CHBrCH3 + NaHSO4 + H2O
What type of reaction is combustion of alcohols? What happens as the number of carbons increases?
• exothermic • As the number of carbon atoms increases the quantity of heat released per mole also increases
What alcohols oxidise and what do they oxidise into?
Primary alcohols -> aldehyde -> carboxylic acids Secondary alcohols -> ketones
Why don’t tertiary alcohols oxidise?
As there are no hydrogen atoms bonded to the carbon atom carrying the hydroxyl group so oxidation would involve breaking a C-C bond
How do you write an oxidising agent in general?
[O]
What is the oxidising agent usually made of?
Solution of potassium dichromate (VI) acified with dilute sulfuric acid and anti bumping granules
What happens if the alcohol is oxidised?
Orange solution containing dichromate ions is reduced to a green solution contains chromium ions
How are aldehydes made?
• gentle heating of primary alcohols with acidified potassium dichromate forms an aldehyde • to ensure the aldehyde doesn’t oxidise further (into a carboxylic acid) the aldehyde is distilled • dichromate ions change colour from orange to green
How are carboxylic acids made?
Primary alcohol is heated strongly under reflux with an excess of acidified potassium dichromate, a carboxylic acid is formed
What are secondary alcohols oxidised into and how are they?
Ketones - secondary alcohol is heated under reflux with the oxidising mixture - dichromate ions once again change colour from orange to green