PODAR INTERNATIONAL SCHOOL (CAMBRIDGE)
Cambridge Assessment International Education
“SARASWATI” BEHIND ARCADIA, HIRANANDANI ESTATE, PATLIPADA, THANE (WEST) - 400607
Grade: _______________ Subject: Chemistry
Worksheet No: AY23-24/Sub / _No__ Date of Issue: __________ Date of Submission: ____________
Unit 19: Reactions of Organic Compounds
9.3 Carboxylic Acids and Esters
A. The Carboxylic Acids
i. Carboxylic acids is the name given to compounds containing the functional group carboxyl, -
COOH
ii. The general formula of a carboxylic acid is CnH2n+1COOH which can be shortened to
just RCOOH
iii. The naming of a carboxylic acid follows the pattern alkane + oic acid
iv. The names and structure of the first four carboxylic acids are shown below
v. Acid properties
The carboxylic acids have the typical properties of acids. For example, they:
• dissolve in water to form acidic solutions with pH values lower than 7
• react with metals to form a salt and hydrogen
• react with bases to form a salt and water
• react with carbonates to form a salt, water and carbon dioxide
• These properties are due to the –COOH functional group.
vi. Formation of Ethanoic Acids by Oxidation of Ethanol:
• Ethanol can undergo oxidation in three different ways:
o Combustion
o Aerobic oxidation
o Treatment with an oxidising agent
Combustion
• Alcohols undergo combustion to form carbon dioxide and water
• The complete combustion of ethanol is as follows:
• Ethanol burns readily with an almost invisible blue flame
• School laboratories use ethanol in spirit burners as it burns cleanly and without
strong odours
Aerobic Oxidation
• Acetobacter is a genus of acetic acid bacteria.
• Acetic acid bacteria are characterized by the ability to convert ethanol to acetic acid in
the presence of oxygen.
• Bacteria in the air (acetobacter) use atmospheric oxygen from air to oxidise the ethanol
in the wine:
ethanol + oxygen → ethanoic acid + water
• The acidic, vinegary taste of wine which has been left open for several days is due to the
presence of ethanoic acid.
• This is what happens to wine when it is left open as the microbial oxidation of ethanol
will produce a weak solution of the carboxylic acid, ethanoic acid, the same acid used
in vinegar.
Treatment with an oxidising agent
• Alcohols undergo oxidation to produce carboxylic acids when treated with oxidising
agents.
• When ethanol is heated with warm potassium manganate (VII) solution, the ethanol
oxidises to ethanoic acid.
• The equation for the reaction is:
CH3CH2OH + 2[O] → CH3COOH + H2O
• The apparatus used for this oxidation is shown above is called REFLUX.
• The condenser is vertically to prevent the volatile alcohol escaping as this would be
dangerous as ethanol is highly flammable.
• During the reaction, the potassium manganate (VII) turns from purple to colourless.
vii. The reactions of aqueous solutions of carboxylic acids with metals and metal carbonates
Dilute carboxylic acids react with metals in the same way as other dilute acids (e.g.
hydrochloric acid) only more slowly.
For example, dilute ethanoic acid reacts with magnesium with a lot of fizzing to produce a
salt and hydrogen, leaving a colourless solution of magnesium ethanoate:
magnesium + ethanoic acid → magnesium ethanoate + hydrogen
Mg (s) + 2CH₃COOH (aq) → (CH₃COO)₂Mg (aq) + H₂ (g)
Dilute carboxylic acids react with metal carbonates as they do with other acids, to give a salt,
carbon dioxide and water.
For example, dilute ethanoic acid reacts with sodium carbonate with a lot of fizzing to produce
a salt, carbon dioxide and water, leaving a colourless solution of sodium ethanoate:
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
Na₂CO₃ (s) + 2CH₃COOH (aq) → 2CH₃COONa (aq) + CO₂ (g) + H₂O (l)
ESTERS
• Structure Esters have the functional group –COO–
• Production Ethyl ethanoate (CH3COOCH2CH3) is the ester produced from ethanol and
ethanoic acid in the presence of concentrated sulfuric acid catalyst.
• Properties They are volatile compounds with distinctive smells and are used as flavourings
and perfumes.
