Chemistry 2010 Jamb Examination

Asbestos in gas-generation setups is used as an inert porous packing that provides a large surface area and improves contact between reactants and any catalytic surface; it does not chemically absorb impurities as its main role. It effectively acts as a support to help the reaction proceed, so the best choice is that it aids/catalyses the reaction.
[Role of asbestos: inert porous support increasing contact acting as a catalytic support]

In many laboratory reactions (for example, copper with dilute nitric acid) the primary gas produced is nitric oxide (NO), which is colourless. On exposure to air it oxidises to nitrogen dioxide (NO₂), which is brown; that is why fumes may turn brown shortly after formation. No numerical calculation is required.

Boiling points depend on molecular mass and intermolecular forces. C₄H₁₀ (butane, small alkane) has the lowest boiling point. C₃H₇OH (propanol) has hydrogen bonding, raising its boiling point above alkanes of similar mass. C₇H₁₆ (heptane, larger alkane) has higher van der Waals forces due to greater molar mass, so its boiling point exceeds that of propanol. Thus, the order is: C₄H₁₀ → C₃H₇OH → C₇H₁₆.

Alkanes, being saturated hydrocarbons, burn readily in oxygen and release large amounts of energy. This makes them suitable as fuels for domestic and industrial purposes. Other listed uses are not primary for alkanes.

The common halogenated solvents used in dry-cleaning are trichloromethane (chloroform) and tetrachloromethane (carbon tetrachloride).

Decolourisation of bromine water indicates unsaturation (C=C or C≡C). Compound Y did not decolourise, so it must be saturated, i.e., an alkane.

Chloroform (CHCl₃) is historically known for its use as an anaesthetic, although less common today due to toxicity concerns.

Calcium carbide and water produce ethyne (acetylene), which was widely used as fuel in miners' lamps due to its bright flame.

Ethanoic acid (CH₃COOH) is highly soluble in water because it can form hydrogen bonds with water molecules. Hydrocarbons and esters are less soluble.

Hydrogenation of benzene (C₆H₆) with hydrogen in the presence of a nickel catalyst yields cyclohexane (C₆H₁₂).