Learn Unit XII: Aldehydes, Ketones and Carboxylic Acids with Free Lessons & Tips

Tollen's Reagent and Its Usefulness: Tollen's reagent is a solution of silver nitrate (AgNO3) mixed with aqueous ammonia (NH3). It is used to distinguish between aldehydes and ketones. Aldehydes are oxidized by Tollen's reagent to form carboxylic acids, while ketones do not react. This reaction is useful in qualitative analysis to identify the presence of aldehydes in a given sample.

Chemical Test to Distinguish Between Benzoic Acid and Phenol: One chemical test to distinguish between benzoic acid and phenol is the sodium bicarbonate test. Benzoic acid reacts with sodium bicarbonate (NaHCO3) to produce effervescence due to the liberation of carbon dioxide gas, while phenol does not react with sodium bicarbonate.

 C6H5COOH + NaHCO3 → C6H5COONa + CO2 + H2O

Chemical Test to Distinguish Between Ethanal and Propanal: Tollens' reagent (ammoniacal silver nitrate) can be used to distinguish between ethanal and propanal. Ethanal gives a silver mirror upon reaction with Tolle

ns' reagent, indicating the presence of an aldehyde group, while propanal also gives a silver mirror but reacts slower than ethanal.
2Ag(NH3)2OH + CH3CHO + 3OH⁻ → 2Ag + CH3COO⁻ + 4NH3 + 2H2O

Chemical Test to Distinguish Between Propanal and Propanone: The Brady's reagent (2,4-dinitrophenylhydrazine) test can be used to distinguish between propanal and propanone. Propanal reacts with Brady's reagent to form a yellow to orange precipitate of 2,4-dinitrophenylhydrazone, while propanone does not react with Brady's reagent.
2,4-dinitrophenylhydrazine + CH3CH2CHO → Orange-yellow precipitate