Chemistry 2023 Jamb Examination

Brass is an alloy made primarily of copper and zinc. The addition of zinc improves the hardness and corrosion resistance of copper while maintaining its ductility.
Other metals may be added in small quantities, but zinc is the major alloying component that defines brass.

When an alkanoic acid reacts with an alcohol in the presence of an acid catalyst such as concentrated \( \text{H}_2\text{SO}_4 \), an ester and water are formed in a process known as esterification.

An alpha particle is a type of nuclear radiation consisting of two protons and two neutrons, which is identical to a helium nucleus. It is represented by the Greek letter \( \alpha \) or symbolically as \( ^4_2He \).
Alpha particles have a positive charge and are relatively heavy compared to beta or gamma radiation. They have low penetration power but can cause significant ionisation within short distances.

Oxidation is defined as the loss of electrons by an atom, ion, or molecule. During oxidation, the oxidation number of the species increases.
Although gaining oxygen can also signify oxidation in some chemical contexts, the most accurate and general definition is the loss of electrons. Conversely, reduction is the gain of electrons.

Litmus paper is an indicator used to test whether a substance is acidic or basic. Blue litmus turns red in acidic solutions because acids have a pH less than 7 and contain hydrogen ions (H⁺) that cause the colour change.
In basic or alkaline solutions, red litmus would turn blue instead.

Electrovalent or ionic bonds are formed when one atom donates electrons to another, resulting in the formation of oppositely charged ions held together by electrostatic attraction.
In sodium chloride (NaCl), sodium donates one electron to chlorine, forming Na⁺ and Cl⁻ ions. The bond between these ions is electrovalent. The other compounds listed involve covalent bonding.

According to Graham’s law of diffusion, the rate of diffusion of a gas is inversely proportional to the square root of its molar mass:\[ \dfrac{r_A}{r_B} = \sqrt{\dfrac{M_B}{M_A}} \]Substituting \( M_A = 32 \) and \( M_B = 64 \):\[ \dfrac{r_A}{r_B} = \sqrt{\dfrac{64}{32}} = \sqrt{2} \approx 1.41 \]Hence, the diffusion rate of gas A is about twice that of gas B, giving a ratio of approximately 2:1.

The contact process is the main industrial method for producing concentrated sulfuric acid (H₂SO₄).
The process involves several stages, including the catalytic oxidation of sulfur dioxide (SO₂) to sulfur trioxide (SO₃) using a vanadium(V) oxide (V₂O₅) catalyst, followed by absorption of SO₃ in concentrated sulfuric acid to form oleum, which is then diluted to form H₂SO₄.

Water exhibits the unusual property of expanding when it freezes. This happens because, in the solid state (ice), water molecules form an open hexagonal structure maintained by hydrogen bonding.
This makes ice less dense than liquid water, allowing it to float. Most other substances contract upon solidification, making this behaviour unique to water.

When sodium reacts with water, the reaction is vigorous and exothermic, forming sodium hydroxide (NaOH) and releasing hydrogen gas (H₂):\[ 2Na + 2H₂O \rightarrow 2NaOH + H₂ \]The hydrogen gas produced may ignite due to the heat of the reaction. This reaction demonstrates the high reactivity of alkali metals with water.