Physical properties of acetic acid: a) It freezes during winters, as its melting point is 290 K. b) It has a characteristic vinegar-like odour. When a pinch of sodium hydrogen carbonate is added to acetic acid in a test tube, a brisk effervescence is observed due to evolution of a colourless and odourless carbon dioxide gas, CO2. This gas when passed through lime water turns it milky due to formation of calcium carbonate, CaCO3. Chemical equations for the reaction: CH3COOH(aq) + NaHCO3(s) → CH3COONa(aq) + H2O(l) + CO2(g) Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)