Reactions with Bases

Carboxylic acids are weak acids, but they still react with bases to form salts called carboxylates. The salt is named from the metal and the acid: ethanoic acid forms ethanoates, e.g. sodium ethanoate, CH₃COONa.With alkalis (neutralisation):
CH₃COOH + NaOH → CH₃COONa + H₂O
With carbonates, carbon dioxide is also given off, so the mixture fizzes:
2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
With hydrogencarbonates:
CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂Test for a carboxylic acid: add sodium hydrogencarbonate or sodium carbonate solution. Effervescence, with a gas that turns limewater milky (CO₂), shows a COOH group. Alcohols do not react, and phenol is too weak an acid to release CO₂ from carbonates, so this test distinguishes carboxylic acids from both.The sodium salts are ionic, so they are soluble in water and are solids with high melting temperatures. Adding a strong acid to a carboxylate turns it back into the carboxylic acid.Worked example: 25.0 cm³ of ethanoic acid is exactly neutralised by 20.0 cm³ of 0.100 mol dm⁻³ NaOH. Amount of NaOH = 0.0200 × 0.100 = 0.00200 mol. The ratio is 1 : 1, so the concentration of the acid = 0.00200 ÷ 0.0250 = 0.0800 mol dm⁻³.