MP Board · Class 12 · Chemistry · Aldehydes, Ketones and Carboxylic AcidsAn organic compound (A) with molecular formula $C2H4O$ reduces Tollens' reagent and gives a yellow precipitate with $I2$ and $NaOH$. Another organic compound (B) with molecular formula $C2H4O2$ turns blue litmus red and reacts with alcohols in the presence of concentrated $H2SO4$ to give a sweet-smelling compound (C). Identify (A), (B), and (C). Write the chemical equations for all the reactions involved.

Identification of Compounds

• Compound (A): The molecular formula $C_2H_4O$ corresponds to Acetaldehyde ($CH_3CHO$). It reduces Tollens' reagent because it is an aldehyde containing a formyl hydrogen, and it gives the iodoform test (yellow precipitate of $CHI_3$) because it contains a $CH_3-CO-$ group.
• Compound (B): The molecular formula $C_2H_4O_2$ corresponds to Acetic acid ($CH_3COOH$). It is a carboxylic acid, which turns blue litmus red and reacts with alcohols to form sweet-smelling esters.
• Compound (C): The sweet-smelling compound formed by the esterification of acetic acid with ethanol is Ethyl acetate ($CH_3COOC_2H_5$).

Step-by-Step Chemical Equations

1. Reaction of Compound (A) with Tollens' reagent: $$CH_3CHO + 2[Ag(NH_3)_2]^+ + 3OH^- \rightarrow CH_3COO^- + 2Ag\downarrow + 4NH_3 + 2H_2O$$ (Silver mirror is formed)

2. Iodoform test for Compound (A): $$CH_3CHO + 3I_2 + 4NaOH \rightarrow CHI_3\downarrow (Yellow) + HCOONa + 3NaI + 3H_2O$$

3. Acidic nature of Compound (B): $$CH_3COOH + H_2O \rightarrow CH_3COO^- + H_3O^+ (Turns blue litmus red)

4. Esterification reaction to form Compound (C): $$CH_3COOH + C_2H_5OH \xrightarrow[Conc. H_2SO_4]{\Delta} CH_3COOC_2H_5 + H_2O$$ (Ethyl acetate, sweet-smelling compound C)