IBDP Chemistry: Carbonxylic Acids

• Contains the carbonyl functional group and a hydroxyl group
• Organic acid- have acidic behaviours due to the close proximity of the carbonyl group with the hydroxyl group
• Weak acids- in equilibrium (OH group capable of donating a proton, H+, only a small fraction of molecules ionise) partially dissociate in water
• Found in medicines, fruit juices, vinegar and rhubarb leaves
• Carboxylic acids and their derivatives are used in organic synthesis as starting materials or intermediates in the formation of more useful compounds e.g. the painkiller aspirin can be synthesised from salicylic acid

• Prefix is the same as alkanes name of the longest carbon chain, remove the ‘e’ at the end and add
• Suffix ‘-oic acid’

1carbon – methanoic acid HCOOH

2carbons – ethanoic acid CH3COOH

3carbons – propanoic acid C2H5COOH

4carbons – butanoic acid C3H7COOH

*REMEMBER* the COOH functional group takes priority and the Carbon atoms is ALWAYS Carbon 1

• Carboxylic acids up to 4 Carbons long are very soluble in water
• C=O and O-H bonds in carboxylic acids are polar so they form hydrogen bonds with water molecules
• Oxygen is more electronegative than Hydrogen and Carbon
• However, as the number of Carbon atoms increases, solubility decreases
• This is because the non-polar Carbon chain has a greater effect on the overall polarity of the molecule
• Dicarboxylic acids have 2 polar carboxyl groups to form hydrogen bonds. They are solids at room temperature and dissolve readily in water

• Take place in redox and neutralisation reactions
• Redox- with metals
• Neutralisation- with bases (alkalis, metal oxides and hydroxides, carbonates)
• Form carboxylate salts, named by removing ‘-ic acid’ and adding‘-ate’
• e.g. carboxylic acid --> carboxylate, carboxylate ions are ionic and so will react with a metal ion
• Carboxylate ions have a 1- charge so when they form salts with group 2 metals, there are 2 carboxylate ions to every 1 metal ion
• E.g. magnesium methanoate

• Aqueous solutions of carboxylic acids react with metals in a redox reaction to form:
  -hydrogen gas
  -carboxylate salt
• Carboxylic acid(aq) + metal(s) --> carboxylate salt(aq) + H2(g)
• Observations:
  • metal disappearing
  • hydrogen gas evolved

e.g. propanoic acid + magnesium --> magnesium propanoate + H2
2CH2CH2COOH + Mg --> (CH3CH2COO-)2Mg2+ + H2

Carboxylic acid(aq) + metal oxide(s) --> salt(aq) + water(l)

• e.g. ethanoic acid + calcium oxide --> calcium ethanoate + water
  2CH3COOH(aq) + CaO(s) --> (CH3COO-)2Ca2+(aq) + H2O(l)

Carboxylic acid(aq) + metal hydroxide(aq)--> salt(aq) + water(l)

• e.g. ethanoic acid + sodium hydroxide --> sodium ethanoate + water
  CH3COOH(aq) + NaOH(aq) --> CH3COO-Na+(aq) + H2O(l)

• Carbon dioxide gas is evolved
• If the carboxylic acid is in excess, a solid carbonate would disappear

Carboxylic acid(aq) + carbonate(aq) --> salt(aq) + water(l) + CO2(g)

• e.g. ethanoic acid + sodium carbonate --> sodium ethanoate + water + carbon dioxide
  2CH3COOH(aq) + Na2CO3(aq) --> 2CH3COO-Na+(aq) + H2O(l) + CO2(g)

This is the end of this topic.