Carboxylic acids: preparation and properties
Compounds containing the carboxyl group –COOH are carboxylic acids; saturated monobasic acids are CₙH₂ₙ₊₁COOH (in formic acid HCOOH the “radical” is just H). Trivial names show their origin: formic (HCOOH), acetic (CH₃COOH), propionic, butyric, valeric, caproic acid; palmitic C₁₅H₃₁COOH and stearic C₁₇H₃₅COOH are higher fatty acids. Systematic names: alkane name + “oic acid” (ethanoic acid), numbering from the carboxyl carbon: 3-methylbutanoic acid. Preparation: oxidizing aldehydes and primary alcohols, hydrolyzing esters, acting on their salts with a strong acid: 2CH₃COONa + H₂SO₄ → 2CH₃COOH + Na₂SO₄. As weak acids they react with metals (2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂), basic oxides, bases (CH₃COOH + NaOH → CH₃COONa + H₂O) and carbonates (2CH₃COOH + CaCO₃ → (CH₃COO)₂Ca + H₂O + CO₂↑). With alcohols they form esters (esterification), and a hydrogen of the radical can be replaced by halogen in light or with a catalyst: CH₃COOH + Cl₂ → ClCH₂COOH + HCl. Formic acid also has an aldehyde group, so it gives the silver mirror reaction. Table vinegar is a dilute (about 3–9 %) solution of acetic acid; the concentrated acid burns the skin.
Read the ingredient label of household vinegar (concentration, percent); do not mix anything. Acetic acid is hazardous when concentrated. In class only the teacher demonstrates reactions with carbonates and magnesium.