Carboxylic acids
❖ • Describe the properties of aqueous ethanoic acid
❖ • Describe the formation of ethanoic acid by the oxidation of ethanol by
fermentation and with acidified potassium manganate(VII)
❖ • Describe ethanoic acid as a typical weak acid
❖ • Describe the reaction of a carboxylic acid with an alcohol in the
presence of a catalyst to give an ester
Ethanoic Acid: Basics
Carboxylic acids
➢ These are a homologous series of organic compounds that all contain the
same functional group: –COOH
➢ They are colourless liquids which are weakly acidic and have typical acidic
properties
➢ They react with alkaline solutions, turn blue litmus red and form salts called
ethanoates
Diagram showing the first three carboxylic acids
Ethanoic Acid
The manufacture of ethanol
• Ethanoic acid is a typically weak acid and dissociates slightly in water,
producing a mildly acidic solution
• The equilibrium lies far to the left during ionization:
CH3COOH ⇌ H+ + CH3COO-
• Ethanoic acid reacts with the more reactive metals, hydroxides and
carbonates
Reactions of ethanoic acid
Reaction with metals
• In the reaction with metals a metal salt and hydrogen gas are
produced
• For example in reaction with magnesium the salt magnesium
ethanoate is formed:
2CH3COOH + Mg → (CH3COO)2Mg + H2
Reaction with hydroxides
• In the reaction with hydroxides a salt and water are formed in
a neutralisation reaction
• For example in reaction with potassium hydroxide the salt
potassium ethanoate is formed:
CH3COOH + KOH → CH3COOK + H2O
Reaction with carbonates
• In the reaction with carbonates a metal salt, water and carbon
dioxide gas are produced
• For example in reaction with potassium carbonate the salt
potassium ethanoate is formed:
2CH3COOH + K2CO3 → 2CH3COOK + H2O + CO2
Ethanoic Acid & Esterification Reactions
• Making carboxylic acids
❖ Oxidation by fermentation
• The microbial oxidation of ethanol will produce a weak solution
of vinegar (ethanoic acid).
• This occurs when a bottle of wine is opened as bacteria in the
air (acetobacter) will use atmospheric oxygen from air to
oxidise the ethanol in the wine:
C2H5OH + O2 → CH3COOH + H2O
The acidic, vinegar taste of wine which has been
left open for several days is due to the presence
of ethanoic acid
❖Oxidation with potassium manganate (VII)
➢ Alcohols can also be oxidised to carboxylic acids by heating
with acidified potassium manganate (VII)
➢ The heating is performed under reflux which involves heating
the reaction mixture in a vessel with a condenser attached to
the top
➢ The condenser prevents the volatile alcohol from escaping the
reaction vessel as alcohols have low boiling points
Diagram showing the experimental setup for the oxidation
with K2MnO4 using reflux apparatus
❖Making esters
➢ Alcohols and carboxylic acids react to make esters in
esterification reactions
➢ Esters are compounds with the functional group R-COO-R
➢ Esters are sweet-smelling oily liquids used in food flavourings
and perfumes
➢ Ethanoic acid will react with ethanol in the presence of
concentrated sulfuric acid (catalyst) to form ethyl ethanoate:
CH3COOH + C2H5OH → CH3COOC2H5 + H2O
Diagram showing the
formation of ethyl ethanoate
❖Naming esters
➢ An ester is made from an alcohol and carboxylic acid
➢ The first part of the name indicates the length of the carbon
chain in the alcohol, and it ends with the letters ‘- yl’
➢ The second part of the name indicates the length of the
carbon chain in the carboxylic acid, and it ends with the
letters ‘- oate’
➢ g. the ester formed from pentanol and butanoic acid is called
pentyl butanoate
Diagram showing the origin of each carbon chain in ester
Examples of esters
2018 summer
