Chemistry – Organic chemistry | e-Consult

(a) Melting Point: Melting point increases with increasing chain length. This is because longer chains lead to stronger London Dispersion Forces (LDFs) between the molecules. The greater the LDFs, the more energy is required to overcome these forces and transition from the solid to the liquid phase. The strength of LDFs increases with increasing molecular surface area.

(b) Solubility in Water: Solubility in water increases with increasing chain length *up to a certain point*. Shorter carboxylic acids (e.g., CH3COOH) are soluble due to hydrogen bonding with water. However, as the carbon chain lengthens, the non-polar hydrocarbon portion of the molecule becomes more dominant. This reduces the ability to form hydrogen bonds with water, leading to decreased solubility. Very long-chain carboxylic acids become insoluble in water.

(c) Acidity: Acidity increases with increasing the number of electron-withdrawing groups attached to the carbon atom bearing the carboxyl group. Electron-withdrawing groups stabilize the conjugate base (carboxylate ion) by delocalizing the negative charge, making it easier for the carboxylic acid to lose a proton. This is due to inductive effects.