Aldehydes and Ketones Quiz

Aldehydes and Ketones

• Aldehydes and ketones are important organic compounds containing a carbonyl group.
• An aldehyde has the structure RCH(=O), while a ketone has the structure R₂C(=O), where R can be alkyl, alkenyl, alkynyl, or aryl groups.

Aim

• Identify the presence of aldehyde or ketone functional groups in a given organic compound.
• Differentiate between aldehydes and ketones.

Theory

• Low molecular weight aldehydes and ketones are volatile compounds.
• Identification is based on addition and oxidation reactions.

Identifying Aldehydes and Ketones

• 2,4-Dinitrophenylhydrazine test: Aldehydes and ketones react with 2,4-dinitrophenylhydrazine, forming a yellow to orange precipitate.
• Sodium bisulfite test: Aldehydes and ketones combine with sodium bisulfite to create water-soluble "aldehyde bisulfite" and "ketone bisulfite" products. Crystallization confirms a carbonyl group.

Differences between Aldehydes and Ketones

• Aldehydes can easily be oxidized to carboxylic acids, while ketones do not oxidize easily.
• This difference in reactivity is used to distinguish them.

Distinguishing Tests (Examples)

• Tollen's test (Silver Mirror Test): Freshly prepared Tollen's reagent (silver ammonia complex) is used. Aldehydes react with it, forming a grey-black precipitate or a silver mirror. The aldehyde is oxidized to an acid, and the silver ion is reduced to its elemental form. Ketones generally do not react.

• Fehling's test: Fehling's solution (a complex compound of Cu²⁺) is used; aldehydes react with it. During the reaction, a red precipitate is formed. A brick red precipitate indicates aldehyde presence. Aromatic aldehydes do not respond to this test.

Fehling's Solution

• Prepared by combining two separate solutions:
  • Fehling's (1): Copper(II) sulfate solution
  • Fehling's (2): Sodium-potassium tartrate (Rochelle salt) solution

Procedure for Tests (Examples):

• Tollen's Test Procedure: The procedure for the Tollen's test involves adding silver nitrate, sodium hydroxide, then ammonia to a test tube, followed by the addition of the substance to be tested. Formation of a silver mirror indicates the presence of an aldehyde.

• Fehling's Test Procedure: Mix equal parts of Fehling's solutions (1 and 2) in a test tube. Add the substance to be tested and heat it. A brick-red precipitate shows an aldehyde's presence.

Test your knowledge on aldehydes and ketones, two essential organic compounds characterized by their carbonyl group. This quiz will help you identify the functional groups in various organic compounds and differentiate between the two types based on their chemical properties and reactions. Challenge yourself with questions related to identification tests and structural differences.