Chemistry 2025 Jamb Examination

Gold is a noble metal located at the very bottom of the electrochemical (reactivity) series. Because it is chemically unreactive (inert), it does not easily form compounds with oxygen or sulphur under normal geological conditions.
As a result, gold is often found in its elemental form, mixed with rock or sand, rather than as an ore that requires chemical reduction. In chemistry, this state is referred to as being found 'free' or 'native' in nature.

The industrial manufacture of tetraoxosulphate(VI) acid (sulphuric acid, H₂SO₄) is known as the Contact Process.
It involves the catalytic oxidation of sulphur(IV) oxide to sulphur(VI) oxide using a vanadium(V) oxide catalyst, followed by the absorption of SO₃ in concentrated sulphuric acid to form oleum, which is then diluted. Other processes listed include the Haber process for ammonia and the Bosch process for hydrogen.

Benzene (C₆H₆) is a cyclic aromatic hydrocarbon. When it undergoes catalytic hydrogenation, three molecules of hydrogen gas are added across the delocalised pi-system in the presence of a nickel catalyst at high temperatures.
This reaction breaks the aromaticity and converts the unsaturated ring into a saturated cyclic alkane called cyclohexane (C₆H₁₂).

Tristearin is a triglyceride (a fat). When it undergoes alkaline hydrolysis (saponification) with a base like NaOH, the ester bonds are broken.
The products are sodium stearate (soap) and propane-1,2,3-triol, commonly known as glycerol. Glycerol contains three hydroxyl (-OH) groups, making it a trihydric alkanol. This is the standard by-product of all soap-making processes involving natural fats and oils.

A reaction is feasible or spontaneous if the Gibbs free energy change (\(\Delta G\)) is negative. The relationship is given by \(\Delta G = \Delta H - T\Delta S\).
In the production of SO₃, three moles of gas react to form two moles of gas, which means entropy decreases (\(\Delta S\) is negative). For \(\Delta G\) to be negative when \(\Delta S\) is negative, the reaction must be exothermic (\(\Delta H\) is negative). However, checking the provided options, if \(\Delta H\) were positive and \(\Delta S\) negative (Option C), \(\Delta G\) would always be positive (not feasible). The feasibility of this specific industrial reaction relies on it being exothermic (negative enthalpy).

Sodium metal is industrially produced by the electrolysis of molten sodium chloride in a specially designed cell.
This process is known as the Downs Process. It uses a graphite anode and a cylindrical steel cathode, with calcium chloride added to the electrolyte to lower the melting point of the sodium chloride.

Chlorofluorocarbons (CFCs) were traditionally used as 'blowing agents' in the manufacture of expanded plastic foams (like styrofoam or polyurethane foam).
In this context, a blowing agent is a substance capable of producing a cellular structure via a foaming process in a polymer that is in a liquid state. While CFCs are also used as refrigerants and propellants, the term 'blowing agent' specifically refers to their application in the foam industry.

Nitric acid (HNO₃) is a powerful oxidising agent. Typically, when it reacts with metals, it produces nitrogen oxides (NO or NO₂) and water instead of hydrogen gas.
However, very dilute nitric acid reacts with very active metals like Magnesium (Mg) and Manganese (Mn) to liberate hydrogen gas. Among the options provided, Magnesium is the classic textbook example of a metal that can achieve this under specific dilute conditions.

The position of an element in the periodic table is determined by its electron configuration:
1. The highest principal quantum number (n) indicates the Period. Here, n=3, so it is in Period 3.
2. The number of valence electrons (electrons in the outermost shell) indicates the Group. Here, the 3rd shell has 2 electrons (3s²), so it is in Group 2.
This element is Magnesium (Mg).

Alkanoic acids follow the general molecular formula C_nH_2nO₂. The simplest empirical formula for this series is CH₂O.
Ethanoic acid (CH₃COOH) has the molecular formula C₂H₄O₂, which simplifies to the empirical formula CH₂O. Its relative molecular mass is calculated as:\[(2 \times 12) + (4 \times 1) + (2 \times 16) = 24 + 4 + 32 = 60\]Therefore, 60 is the molecular mass that fits the empirical formula for a common alkanoic acid.