2024 - JAMB Chemistry Past Questions and Answers - page 2

Here's how to solve this problem:

1. Determine the ratio of molar masses: The molar mass ratio of X to Y is 72:6, which simplifies to 12:1.
2. Calculate the molecular formula: Since the empirical formula is XY, the molecule contains 1 part X and 1 part Y. The molar mass of XY is (1 * 72) + (1 * 6) = 78. To find the molecular formula, additional information like vapor density is required.
3. Calculate molar mass using vapor density: Vapor density (VD) is half the molar mass (M). Therefore, M = 2 * VD.
4. Finding the correct answer: Using the options to check, if VD = 33 (Option A), then M = 66; if VD = 66 (Option B), then M = 132; if VD = 39 (Option C), then M = 78. The vapor density most consistent with the molecular formula XY is likely 39.

H₂SO₄ is a strong acid and dissociates completely in water. Each molecule yields two H⁺ ions.

1. Calculate the concentration of H⁺ ions: 0.001 mol/dm³ * 2 = 0.002 mol/dm³.
2. Calculate pH: pH = -log₁₀[H⁺] = -log₁₀(2 x 10^-3) = -(log₁₀2 + log₁₀10^-3) = -(0.3 - 3) = 2.7

Here's how aqueous NaOH can test for these ions:

• Ca²⁺: Forms a white precipitate of Ca(OH)₂.
• Zn²⁺: Forms a white precipitate of Zn(OH)₂, which dissolves in excess NaOH to form [Zn(OH)₄]^2-.
• Cu²⁺: Forms a blue precipitate of Cu(OH)₂.

Therefore, NaOH can test for all three ions.

Rust is primarily hydrated iron(III) oxide, formed when iron reacts with oxygen and water. The hydration is a key aspect.

The gas that turns lime water milky is carbon dioxide (CO₂), formed when a carbonate reacts with an acid. CO₂ reacts with limewater (Ca(OH)₂) to produce insoluble CaCO₃, giving a milky appearance.

The Pauli Exclusion Principle states that no two electrons in the same atom can have the same set of four quantum numbers. Each orbital can hold a maximum of two electrons with opposite spins.

In a strong acid-weak base titration, the equivalence point is acidic. Suitable indicators are:

• Methyl orange: pH 3.1-4.4, red to yellow, suitable.
• Phenolphthalein: pH 8.3-10, not suitable.
• Bromothymol blue: pH 6.0-7.6, near neutral, less suitable.
• Methyl red: pH 4.4-6.2, also suitable, though methyl orange is preferred.

1. Half-reaction: Ag⁺ + e⁻ → Ag

2. Moles of Ag = 180 g / 108 g/mol = 1.67 mol

3. Quantity of electricity: 1 mole of Ag requires 1 Faraday, so 1.67 moles require 1.67 Faradays.

In electroplating:

• Cathode: Spoon (where reduction occurs, silver is deposited).
• Anode: Silver rod (provides Ag⁺ ions).
• Electrolyte: Soluble silver salt (e.g., AgNO₃) providing Ag⁺ ions.

According to Graham's Law of Diffusion, rate ∝ 1/√M (molar mass). Given Rate(X) = 2 * Rate(Y), we have:

√(M(Y)/M(X)) = 2 → M(Y)/M(X) = 4 → M(Y) = 4 * M(X).
Therefore, Gas Y is four times as heavy as Gas X.