CBSE 12th Chemistry Question Paper 2023 (Set 3)

The dissolution of ammonium chloride is an endothermic process (indicated by the solution feeling cool). According to Le Chatelier's principle, increasing the temperature favours the endothermic direction, thus increasing solubility. Furthermore, powdered salt increases the surface area compared to crystals, leading to a faster rate of dissolution. Therefore, powdered salt in hot water is the ideal condition.

Lanthanoid contraction refers to the steady decrease in atomic and ionic radii of lanthanoids as the atomic number increases. This is primarily due to the poor shielding effect of 4f electrons, which allows the effective nuclear charge to exert a greater pull on the outer shell electrons, drawing them closer to the nucleus.

The reaction of an amide (CH3CONH2) with NaOH and Br2 is the Hofmann bromamide degradation reaction. This reaction converts a primary amide into a primary amine with one carbon atom less than the original amide. Thus, CH3CONH2 (acetamide) yields CH3NH2 (methanamine).

The reaction of alcohol with HCl in the presence of ZnCl2 is known as the Lucas test. This reaction proceeds via the formation of a carbocation intermediate. Tertiary (3°) alcohols form stable carbocations easily, followed by secondary (2°), and then primary (1°) alcohols. Thus, the order of reactivity is 3° > 2° > 1°, or 1 < 2 < 3.

Ionisation isomerism occurs when the counter ion in a coordination compound is a potential ligand and can displace a ligand which can then become the counter ion. Here, the sulphate ion (SO4^2-) and the bromide ion (Br-) exchange positions between the coordination sphere and the counter ion position.