Chemistry 2024 Jamb Examination

Carbon(IV) oxide, also known as carbon dioxide (CO₂), is a minor constituent of the Earth's atmosphere. It makes up approximately 0.03% of the air by volume.
This concentration can vary slightly due to factors such as human activities and natural processes like respiration and volcanic eruptions.
Therefore, the correct percentage of CO₂ in the air is 0.03%.

A physical change involves a change in the physical state of a substance without altering its chemical composition.
Boiling of water is a physical change because the water molecules remain the same, only changing from liquid to vapour.
The other options involve chemical reactions where new substances are formed.

Boyle’s law states that the pressure of a given mass of gas is inversely proportional to its volume at constant temperature.
Mathematically, this is expressed as \( PV = k \), where \( P \) is pressure, \( V \) is volume, and \( k \) is a constant.
Therefore, when pressure increases, volume decreases, and vice versa, provided temperature remains constant.

Given:
Volume of gas = 560 cm³ = 0.56 dm³
Mass = 0.4 g
Molar volume = 22.4 dm³

Molar mass \( M = \dfrac{22.4}{0.56} \times 0.4 = 16.0 \; \text{g mol}^{-1} \)
Vapour density (VD) = \( \dfrac{M}{2} = \dfrac{16}{2} = 8.0 \)
Thus, the vapour density of the gas is 8.0.

The subsidiary quantum number, \( l \), determines the shape of the orbital.
When \( l = 0 \), the orbital is an s-orbital which is spherical in shape.
When \( l = 1 \), it corresponds to a p-orbital which has a dumb-bell shape.
Therefore, for \( l = 1 \), the orbital is dumb-bell shaped.

Esterification involves the reaction of a carboxylic acid with an alcohol to form an ester and water.
It is a condensation reaction because two molecules combine with the elimination of a small molecule, usually water.
Hence, esterification is analogous to a condensation reaction.

The compound \( \text{CH}_3\text{CH}_2\text{C(CH}_3\text{)=C(CH}_3\text{)}_2 \) contains five carbon atoms in the main chain, giving the parent name pentene.
The double bond starts at carbon 2, and two methyl groups are attached at carbons 2 and 3.
Therefore, its IUPAC name is 2,3-dimethylpent-2-ene.

Concentrated sulphuric acid at high temperature acts as a dehydrating agent on ethanol.
The reaction removes a molecule of water from ethanol to form ethene (C₂H₄).
This process is known as a dehydration reaction because water is eliminated from the reactant.

In hydrogen sulphide, H₂S, hydrogen has oxidation state +1 each.
Using the algebraic method: \(2(+1) + x = 0\) where \(x\) is the oxidation state of sulphur.
Therefore \(x = -2\).
The product S(s) is elemental sulphur with oxidation state 0.
Hence the change in oxidation state of sulphur is from \(-2\) to \(0\).

Mass number (A) = protons (Z) + neutrons (N).
The common stable nuclide with mass number 31 is phosphorus-31, which has atomic number \(Z = 15\).
For a neutral atom, electrons = protons = 15.
Neutrons = \(A - Z = 31 - 15 = 16\).
Therefore the numbers of electrons and neutrons respectively are 15 and 16.