Question

Compare the volatility and odor of stearic acid and sucrose. which is more volatile? why? is it possible for a compound to be volatile but have no odor? explain.

Answer 1

Stearic acid is more volatile than sucrose. Stearic acid is non polar, which means it dissolves in non polar solvent such as hexane. Sucrose on the other hand is a polar molecule, as it is soluble in water like the monosaccharides. Volatile is a feature in which something is evaporating or vaporizing readily under normal conditions. Stearic acid unlike sucrose has a pungent smell . Pure sucrose is mostly often prepared as a fine, colorless, odorless crystalline powder. It is possible for a compound to be volatile but odorless.

Answer 2

Stearic acid is more volatile than sucrose.

CH₃-(CH₂)₁₆-COOH, stearic acid has a long hydrocarbon chain and a carboxylic group at one. The long C-H main chain has predominantly London dispersion forces, which are weak intermolecular forces. Only the –COOH functional group has hydrogen bonding and dipole-dipole forces.  

Sucrose is a disaccharide made up of glucose and fructose. Both glucose and fructose are monosaccharide made up of several –OH(hydroxyl) groups. Sucrose has predominantly hydrogen bonding because of the several hydroxyl groups. Hydrogen bonding is a stronger intermolecular force of attraction than London dispersion forces.

Therefore, the stronger intermolecular forces of attraction (H-bonding) make sucrose less volatile and the stronger intermolecular forces of attraction (London dispersion forces) make stearic acid more volatile.  

Yes it is possible for a compound to be volatile but have no odor. Water is volatile but it has no odor. Human olfactory system is unique and complex. Our nose is able to detect certain molecules and unable to detect others. That is why we do not smell water but we do smell vinegar.