Chemistry 2024 Jamb Examination

In a titration involving a strong acid and a weak base, the pH at the equivalence point is less than 7. Methyl orange changes colour in the acidic range (3.1–4.4), making it suitable for detecting the end point. Phenolphthalein is better for weak acid-strong base titrations as it changes colour in the basic range.

Air-derived nitrogen may contain traces of oxygen, inert gases like argon, and water vapour. Carbon (IV) oxide (CO2) is present only in very minute amounts and is negligible; thus, it is generally considered not a major impurity. Therefore, CO2 is the exception.

A solubility curve represents how the solubility of a substance varies with temperature, typically measured in grams of solute per 100 g of solvent. Pressure mainly affects gas solubility, not solids, and volume or concentration are not axes for a solubility curve.

Vapour density (VD) is half the molar mass: \( VD = \dfrac{M}{2} \).
Number of moles of gas = \( \dfrac{5.6}{22.4} = 0.25 \text{ mol} \)
Molar mass = \( \dfrac{11.0}{0.25} = 44 \) g/mol
VD = 44 ÷ 2 = 22. Therefore, the vapour density is 22.

Van der Waals forces are weak intermolecular forces present between neutral molecules due to temporary dipoles. They are not the forces between ions (cations or anions) or single atoms in a lattice, though atoms can exhibit London dispersion as a type of Van der Waals force.

Nitrogen has five electrons in its outer shell. The 2p electrons occupy different orbitals singly according to Hund's rule, maximising spin multiplicity. This is a normal ground-state configuration, obeying the rules governing electron configuration, not an excited or unstable state.

The reaction between H2 and Cl2 is photochemically initiated by visible light, particularly sunlight. Sunlight provides the energy to break Cl2 into radicals, which then propagate a chain reaction to form HCl explosively. Diffused light is too weak to initiate the reaction.

Strong and weak acids refer to the degree of ionization in aqueous solution. Strong acids ionize almost completely, releasing most of their H+ ions, whereas weak acids ionize only partially. It is not simply the amount of H+ but the proportion of molecules ionized.

Water-glass is sodium silicate, which is composed primarily of sodium trioxosilicate(IV), Na2SiO3. The other options contain calcium or sulphur, which are not the main constituents of water-glass.

Reactivity increases down the reactivity series: metals like gold are least reactive, while calcium is highly reactive. The correct order from least to most reactive is Au < Cu < Sn < Fe < Ca.