Carboxyl Group: Carboxyl group in carboxylic acid.
Uses: Carboxylic acids found in medicines and vinegar.
Naming: Methanoic acid HCOOH is simplest. As suffix starts with vowel, shorten butane to
butan.
Solubility of Carboxylic Acids:
– Polar C=O bond and O-H bonds in carboxylic acids form hydrogen bonds with water
molecules.
– As the number of carbon atoms increases, solubility decreases as a greater proportion of the
molecule non- polar. This cannot form H bonds with H2O molecules.
– The more O’s with lone pairs on a compound the more soluble
Dicarboxylic Acids: Dicarboxylic acids have two polar carboxylic groups to form H bonds. They
are solids at room temperature and dissolve readily.
Strength of Carboxylic Acids: Carboxylic acids are weak acids. When dissolved in water,
carboxylic acids partially dissociate- HCOOH (aq) ⇌ H+ (aq) + HCOO- (aq).
Carboxylate Salts: In neutralisation and redox reactions, carboxylic acids form carboxylate salts.
The carboxylate ion in salt is named by changing –oic acid to –ate.
Don’t bother writing charges.
1) Redox Reaction- Carboxylic with Metals: Aqueous carboxylic
acid react with metal in redox reaction to form hydrogen gas and carboxylate salt.
Would observe metal disappearing and effervescence as hydrogen gas evolved. Propanoic acid-
– 2CH3CH2COOH (aq) + Mg (s) -> (CH3CH2COO-)2Mg2+ (aq) + H2 (g)
– Ionic equation: 2H+ + Mg -> Mg2+ + H2
2) Neutralisation Reactions- Carboxylic Acids with
Bases…
In all of these, the carboxylate formed is with metals only.
Reaction with Metal Oxides: Forms salt and water. Ethanoic acid + calcium oxide -> calcium
ethanoate + water.
– 2CH3COOH (aq) + CaO (s) -> (CH2COO-)2Ca2+ (aq) + H2O (l)
Reaction with Alkalis: Forms salt and water. May not see a reaction as form aqueous solution of
salt. Ethanoic acid + sodium hydroxide -> sodium ethanoate (as 2C) + water.
– 2CH3COOH (aq) + NaOH (aq) -> (CH2COO-)2Na+
(aq) + H2O (l)
– H+ (aq) + OH- (aq) -> H2O (l)
Reaction with Carbonates: If carboxylic acid in excess, solid carbonate disappears. Ethanoic acid
+ sodium carbonate -> sodium ethanoate + water + carbon dioxide.
– 2CH3COOH (aq) + Na2CO3 (aq) -> 2CH3COO-Na+
(aq) + H2O (l) + CO2 (g)
– Ionic equation: 2H+ (from organic acid) + CO3
2- -> H2O (l) + CO2 (g)
Test for Carboxyl Group: The neutralisation of carboxylic acids with carbonate provides a test
for carboxyl groups. Carboxylic acidic enough to react with carbonates.