Chemistry 2020 Jamb Examination

Tetrachloromethane (CCl₄), also known as carbon tetrachloride, is a non-flammable solvent widely used in industry for removing grease and oils from machinery and fabrics.
It effectively dissolves organic materials due to its non-polar nature and was historically used in cleaning and degreasing operations before being restricted for environmental and health reasons.

The balanced chemical equation is:
\( 2H_2 + O_2 \rightarrow 2H_2O \)
Molar mass of H₂ = 2 g/mol, molar mass of H₂O = 18 g/mol.
From the equation, 4 g of H₂ produces 36 g of H₂O.
Therefore, 8 g of H₂ produces \( \dfrac{36}{4} \times 8 = 72 \; \text{g} \) of water.

In acidic solutions, proteins undergo hydrolysis, breaking down into smaller peptide units and eventually into amino acids.
This process involves the cleavage of peptide bonds by water molecules in the presence of an acid catalyst, which disrupts the protein’s primary structure.

Alkanals are aldehydes with the general formula \( RCHO \), where R represents an alkyl group and the functional group is the formyl group (–CHO).
The carbonyl carbon in aldehydes is always bonded to at least one hydrogen atom, distinguishing them from ketones (\( R₂CO \)).

Cathode rays consist of streams of electrons, which carry a negative charge.
When they strike the electrode of an electrometer, electrons are deposited, causing the instrument to become negatively charged.
This experiment helped in demonstrating the electron’s negative nature.

Sublimation is the process in which a solid changes directly into a gas without passing through the liquid phase.
Examples include iodine, dry ice (solid CO₂), and ammonium chloride.
This occurs under specific temperature and pressure conditions.

Halogen atoms (Group VIIA elements) have seven valence electrons.
When they gain one electron, they achieve a stable octet configuration with eight valence electrons, forming halide ions (e.g., Cl⁻, Br⁻, I⁻).

Aluminium hydroxide acts as a mordant in the dyeing industry.
A mordant is a substance that helps fix dyes on fabrics by forming insoluble complexes with the dye molecules, improving colour fastness and brightness.

Oxygen is the most abundant element in the Earth’s crust, making up about 46% by mass.
It is found in oxides, silicates, and other minerals, as well as in water, forming a major component of the Earth’s composition.

A mixture of carbon(II) oxide (CO) and carbon(IV) oxide (CO₂) can be purified by passing it through concentrated sodium hydroxide (NaOH).
NaOH absorbs CO₂ to form sodium carbonate, while CO remains unreacted and passes through, yielding pure CO gas.