2.7 Alcohols and carboxylic acids

General formula of alcohols

Cn H2n+1 OH

Solubility of alcohols

Soluble as they can hydrogen bond with water

What happens to solubility as carbon chain length increases

Decreases

Hydrocarbon chain disrupts bonding between other water molecules

Volatility

Ease with which a liquid can turn into a vapour

What do alcohols have a higher boiling point than

Their corresponding alkane

Alcohol can undergo hydrogen bonding between alcohol groups - increasing bp

How is ethanol produced from ethene

Addition reaction with steam in the presence of a H3PO4 catalyst

Conditions for ethanol production

300 degrees

6MPa

Where does the ethene come from

Catalytic cracking of long chain alkanes

Another way to produce ethanol

Anaerobic fermentation of sugar

Conditions needed for fermentation of sugar

Yeast

37 degrees

Why doesn’t the fermentation process make 100% concentrated ethanol

Fermentation stops when the concentration of ethanol reaches around 15% because it starts to kill the yeast

Uses of alcohols

Drinks

Solvents

Biofuel

Petrol additive to improve combustion

Biofuels

Made from crops e.g wheat

E.g bioethanol

Car engines will need to adapt to these fuels

Bioethanol

Produced from biomass by hydrolysis and sugar fermentation

Can be mixed with petrol and burnt in petrol engines

Biobutanol

Biomass permeated using bacterial enzymes

Can also be mixed with petrol and burnt in petrol engines

Biodiesel

Produced from crops e.g oil seed rape

Advantages of biofuels

Renewable

Carbon neutral

Economic security

Disadvantages of biofuels

Land use

Use of resources

Elimination reactions

Dehydration

Product of a dehydrated alcohol

Alkene

What is needed for an elimination reaction of alcohols

H2SO4 OR H3PO4

Dehydration of secondary alcohols

2 possible products formed

Primary alcohol

OH group is on a carbon which is bonded to one other carbon atom

Secondary alcohol

OH group on a carbon atom which is bonded to two other carbon atoms

Tertiary alcohol

OH group on a carbon which is bonded to three other carbon atoms

Why is the combustion of alcohol highly exothermic

They have high enthalpies of combustion

Products of the combustion of alcohols

Carbon dioxide and water

What is needed to oxidise an alcohol

Acidified aqueous dichromate

E.g acidified potassium dichromate

Products of oxidation of a primary alcohol

Aldehyde

Further oxidised to a carboxylic acid

Products of oxidation of a secondary alcohol

Ketone

Products of oxidation of a tertiary alcohol

No reaction

How can aldehydes be collected

Distillation

Suffix of an aldehyde

Al

How can a carboxylic acid be collected

Distillation

How can ethanoic acid be identified

Smell of vinegar

Turns litmus paper red

Odours of ketones

Wood and fruit

What happens during the oxidation process of an alcohol

Orange colour changes to green

How to identify a primary alcohol

Colour change from orange to green

Turns blue litmus red

How to identify a secondary alcohol

Colour change from orange to green

No effect on litmus

How to identify a tertiary alcohol

No colour change

How do carboxylic acids form

Oxidation of primary alcohols using acidified dichromate

In a carboxylic acid the carbonyl carbon is counted as

Part of the main chain

Is the first carbon in the chain

General formula of a carboxylic acid

Cn H2n+1 COOH

Solubility of carboxylic acids

OH group is polar - undergoes H bonding with water molecules

Longer carbon chains become progressively less soluble as hydrocarbon chain is non polar

Dimer

Hydrogen bonding between 2 carboxylic molecules

Why do dimers have increased boiling points

More energy is needed to separate them

Volatility decreases

What type of acid are carboxylic acids

Weak

Complete dissociation does not occur

Reaction of a carboxylic acid with a metal

Forms salt and H gas

See effervescence

Reaction of carboxylic acid with a base

Forms salt and water

No visible change will be seen EXCEPT copper involved will form a blue solution

Reaction of carboxylic acids with carbonates and hydrogen carbonates

Forms salt carbon dioxide and water

Reactions of carboxylic acids to form esters

Carboxylic acid reacts with an alcohol in the presence of an acid catalyst to form an ester

Type of acid used to form esters

Sulphuric acid

Which bond is broken in the formation of an ester

OH bond in the alcohol

Bi product of the formation of an ester

Water