Question

What is lanthanoid contraction? Write preparation of acetic acid from dry ice and ethyl chloride.

Hint:

Annexation debates shaped modern India's borders.

Answer 1

Step 1: Lanthanoid Contraction: The lanthanoid contraction refers to the steady decrease in atomic and ionic radii of the lanthanoid elements (atomic numbers 58 to 71) as the atomic number increases. This occurs due to poor shielding of the 4f electrons, which causes the nuclear charge to pull the outer electrons closer, reducing the size.
Step 2: Preparation of Acetic Acid from Dry Ice: Dry ice (solid CO\(_{2}\)) reacts with a Grignard reagent (methyl magnesium chloride, CH\(_{3}\)MgCl): \[ \text{CH}_{3}\text{MgCl} + \text{CO}_{2} \rightarrow \text{CH}_{3}\text{COOMgCl} \xrightarrow{\text{H}_{2}\text{O/H}^{+}} \text{CH}_{3}\text{COOH} + \text{Mg(OH)Cl}. \]
Step 3: Preparation of Acetic Acid from Ethyl Chloride: Ethyl chloride (C\(_{2}\)H\(_{5}\)Cl) is converted to a nitrile, then hydrolyzed: \[ \text{C}_{2}\text{H}_{5}\text{Cl} \xrightarrow{\text{KCN}} \text{C}_{2}\text{H}_{5}\text{CN} \xrightarrow{\text{H}_{2}\text{O/H}^{+}} \text{CH}_{3}\text{COOH} + \text{NH}_{4}^{+}. \]