Chemistry 2025 Jamb Examination

Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled from crude oil into high-octane liquid products. This usually involves converting straight-chain alkanes into branched-chain alkanes or cyclic hydrocarbons (aromatics).
The conversion of cyclohexane (a cycloalkane) to benzene (an aromatic hydrocarbon) is a classic example of dehydrogenation, which is a key reaction in the reforming process to improve the octane rating of fuel.

Carbon(II) oxide, or carbon monoxide (CO), is a highly toxic gas produced primarily by the incomplete combustion of carbon-containing fuels such as petrol, coal, and wood.
When engines or furnaces do not have enough oxygen to completely convert carbon to carbon(IV) oxide (CO₂), CO is formed as a major pollutant. Photochemical smog is a result of pollutants, respiration produces CO₂, and sewage decomposition mainly produces methane and hydrogen sulphide.

According to Le Chatelier's Principle, a change in pressure only affects a gaseous system at equilibrium if there is a difference in the number of moles of gas between the reactants and the products.
If the number of moles of gas is the same on both sides (meaning there is no change in volume), then increasing or decreasing the pressure will not shift the equilibrium position in either direction. The system remains balanced because both sides are affected equally.

To name an ester, we identify the alkyl group derived from the alkanol and the acyl group derived from the alkanoic acid.
Looking at the structure (CH₃CH₂COOCH₂CH₃):
1. The part attached to the single-bonded oxygen is \(-CH_2CH_3\), which is an ethyl group.
2. The part containing the carbonyl group (C=O) has three carbons (CH₃CH₂CO-), which is derived from propanoic acid.
Combining these, the name is ethyl propanoate.

The rate of reaction can be calculated as the amount of reactant used divided by the time taken. We need the final answer in grams per hour (g/hr).
First, convert the time from minutes to hours:\[\text{Time} = 10 \text{ min} = \frac{10}{60} \text{ hr} = \frac{1}{6} \text{ hr}\]Now, calculate the rate:\[\text{Rate} = \frac{\text{Mass}}{\text{Time}} = \frac{5 \text{ g}}{1/6 \text{ hr}}\]\[\text{Rate} = 5 \times 6 = 30 \text{ g/hr}\]

Pinking, also known as 'knocking', is the sharp metallic noise produced in an internal combustion engine when the fuel-air mixture ignites prematurely or unevenly.
To prevent this, petrol is evaluated and assigned an 'octane rating'. Fuels with higher octane ratings burn more smoothly. Processes like reforming and cracking are actually used to *improve* the quality of petrol to prevent pinking, but the purpose of the final evaluation is to ensure the fuel meets the necessary standards to avoid engine damage.

Aluminium (Al) is widely used as a packaging material, especially in the form of aluminium foil and beverage cans.
This is because it is lightweight, non-toxic, and highly resistant to corrosion due to the formation of a protective oxide layer. Copper is too expensive and heavy, Iron (in the form of steel) is used but often needs coating to prevent rust, and Sodium is far too reactive to be used for any structural or packaging purpose.

Charles' Law states that for a fixed mass of gas at constant pressure, the volume is directly proportional to its absolute temperature (measured in Kelvin).
Mathematically, this is expressed as \( V \propto T \) or \( rac{V}{T} = k \). When comparing two states of the same gas, it is written as:\[rac{V_1}{T_1} = rac{V_2}{T_2}\]

The basicity of an acid is the number of replaceable hydrogen ions (H⁺) present in one molecule of the acid.
C₂H₂O₄ is the molecular formula for oxalic acid, which has the structural formula (COOH)₂. Each of the two carboxyl groups can release one hydrogen ion. Since it has two replaceable hydrogen atoms, its basicity is 2, making it a dibasic acid.

Fermentation is the biochemical process in which enzymes (specifically zymase from yeast) convert sugars like glucose into ethanol and carbon(IV) oxide in the absence of oxygen.
The chemical equation is:\[C_6H_{12}O_6 \xrightarrow{\text{zymase}} 2C_2H_5OH + 2CO_2\]This process is used extensively in the production of alcoholic beverages and biofuels.