Question

4. a) Identify the difference(s) in structure of adipic acid (CAS 124-04-9) and Malonic Acid (CAS 141-82-2).

b) Explain how this difference(s) in structure accounts for the solubility of the two compounds in water. Focus on polarity and intermolecular forces of the molecules and the solvent.

c) Explain why the compound vanillin (CAS 121-33-5) demonstrates different solubility in ethyl acetate and hexane. Focus on the structure and the intermolecular forces of the solute and solvent.

Answer 1

a. Malonic acid is :

HOOC-CH₂ - COOH

Adipic acid is:

HOOC- CH₂-CH_2^-CH₂-CH₂-COOH

(b) Both the acid contains two polar carboxylic acid (-COOH) groups. But adipic acid contains more alkyl groups than malonic acid. As the alkyl chain in adipic acid is more lengthy than malonic acid; adipic acid is less polar than malonic acid.

So; adipic acid is more soluble in less polar solvent like hexane whereas malonic acid is more soluble in more polar solvent like ethyl acetate.

(c) Vanilin contains polar functional groups like aromatic ring; -OH ; methoxy (OCH3) and aldehyde (- CHO).

For the reason, it can form dipole -dipole interactions with polar solvents. In addition; it can form H-bonds with polar solvent that has H- bond acceptor atoms like ethyl acetate.

Due to the above jntermolecular forces formed between vanillin and polar solvents; vanillin is highly soluble in polar solvent like ethyl acetate abd is less doluble in non-polar solvent like hexane.