Chemistry JAMB Questions and Answers 2027

Correct Answer: C. Mg₃X₂

Explanation/Tip: Element X has 5 valence electrons (Group 5), so it forms an anion with a valency of 3 (X^3-). Magnesium is in Group 2 and forms a cation with a valency of 2 (Mg²⁺). By cross-valency, the formula is Mg₃X₂.

Correct Answer: A. Methane (CH₄)

Explanation/Tip: According to Graham’s Law, rate of diffusion is inversely proportional to the square root of vapor density. Molar mass of SO₂ = 64 g/mol. For a gas to diffuse twice as fast, its molar mass must be 64 / (2²) = 16 g/mol. Methane (CH₄) has a molar mass of 16 g/mol.

Correct Answer: B. +6

Explanation/Tip: Let the oxidation number of Cr be x. For Cr₂O₇^2-, 2(x) + 7(-2) = -2. Therefore, 2x – 14 = -2, 2x = 12, and x = +6.

Correct Answer: C. Sodium

Explanation/Tip: Highly reactive metals like sodium are extracted by the electrolysis of molten sodium chloride (Downs process). Aluminum is extracted via Hall-Héroult process using molten bauxite dissolved in cryolite.

Correct Answer: D. Increase in pressure

Explanation/Tip: According to Le Chatelier’s principle, an increase in pressure favors the side with fewer moles of gas. The reactants have 4 moles while the product has 2 moles, so high pressure shifts equilibrium to the right.

Correct Answer: B. 20.0 cm³

Explanation/Tip: Use (C_aV_a / C_bV_b) = n_a / n_b. Here, n_a = 1, n_b = 1. (0.20 × 25) / (0.25 × V_b) = 1/1. V_b = 20.0 cm³.

Correct Answer: B. 4-methylpentan-2-ol

Explanation/Tip: Numbering starts from the end closest to the principal functional group (-OH gets locant 2). The longest carbon chain has 5 carbons, with a methyl substituent at carbon 4.

Correct Answer: B. Iodine

Explanation/Tip: Sublimation is the direct transition from solid to gas without passing through the liquid state. Common examples include iodine, dry ice (solid CO₂), and ammonium chloride.

Correct Answer: B. Oxygen

Explanation/Tip: At the anode, hydroxyl ions (OH^–) are discharged preferentially over sulfate ions due to their position in the electrochemical series, producing oxygen gas and water.

Correct Answer: B. But-2-ene

Explanation/Tip: Cis-trans isomerism occurs in alkenes where each carbon atom of the double bond is attached to two different groups. But-2-ene satisfies this condition.

Correct Answer: B. 0.64 g

Explanation/Tip: Using Faraday’s law, M = (Molar Mass × Current × Time) / (Valency × F) = (64 × 2 × 965) / (2 × 96500) = 0.64 g.

Correct Answer: C. Phenolphthalein

Explanation/Tip: The equivalence point of a weak acid-strong base titration lies in the alkaline pH range (8 to 10). Phenolphthalein changes color precisely in this range (pH 8.3 – 10.0).

Correct Answer: B. Magnesium hydrogen carbonate

Explanation/Tip: Temporary hardness is caused by dissolved hydrogen carbonates of calcium and magnesium, which can be removed simply by boiling.

Correct Answer: A. Hydrogenation in the presence of a nickel catalyst

Explanation/Tip: Vegetable oils are unsaturated fats containing double bonds. Adding hydrogen gas in the presence of a nickel catalyst at 180°C converts liquid oil into solid margarine.

Correct Answer: B. 46.7%

Explanation/Tip: Molar mass of CO(NH₂)₂ = 12 + 16 + 2(14 + 4) = 60 g/mol. Total mass of nitrogen = 28 g/mol. Percentage = (28 / 60) × 100 = 46.67%.

Correct Answer: C. Hydrogen chloride gas

Explanation/Tip: NaCl + H₂SO₄ → NaHSO₄ + HCl. Concentrated sulfuric acid displaces the volatile hydrogen chloride gas from its salt.

Correct Answer: B. Hematite

Explanation/Tip: Hematite (Fe₂O₃) is the primary ore of iron processed in the blast furnace alongside coke, limestone, and hot air.

Correct Answer: B. Electronegativity

Explanation/Tip: Electronegativity decreases down a group as atomic size increases, reducing the nuclear attraction for bonding electrons. Fluorine is the most electronegative halogen.

Correct Answer: B. sp²

Explanation/Tip: Ethene contains a carbon-carbon double bond. Each carbon forms three sigma bonds, resulting in planar trigonal geometry with sp² hybridization.

Correct Answer: B. 4

Explanation/Tip: pH is calculated as -log[H⁺]. Therefore, -log(1.0 × 10^-4) = 4.

Correct Answer: B. Sulfur dioxide

Explanation/Tip: Sulfur dioxide is a strong reducing agent. It reduces orange dichromate ions (Cr₂O₇^2-) to green chromium ions (Cr³⁺).

Correct Answer: B. Condensation polymerization

Explanation/Tip: Terylene (polyester) is formed by the condensation reaction between benzene-1,4-dicarboxylic acid and ethane-1,2-diol with the elimination of water molecules.

Correct Answer: C. Copper

Explanation/Tip: Metals below hydrogen in the electrochemical series (like copper, silver, and gold) cannot displace hydrogen from dilute acids.

Correct Answer: A. Ethyl ethanoate

Explanation/Tip: Esters are named as alkyl alkanoates. The alkyl group comes from the alcohol (ethyl) and the alkanoate part comes from the carboxylic acid (ethanoate).

Correct Answer: B. Lower the melting point of alumina

Explanation/Tip: Pure alumina has a very high melting point (~2050°C). Adding molten cryolite (Na₃AlF₆) lowers the melting point to about 950°C and improves conductivity.

Correct Answer: B. Magnesium

Explanation/Tip: Magnesium has a higher first ionization energy than aluminum because its 3s orbital is completely filled, providing extra stability.

Correct Answer: B. 2.24 dm³

Explanation/Tip: Molar mass of CaCO₃ = 100 g/mol. Moles = 10 / 100 = 0.1 mol. From CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂, volume = 0.1 × 22.4 = 2.24 dm³.

Correct Answer: B. Sodium chloride

Explanation/Tip: Chloride ions form a white precipitate of silver chloride (AgCl) with silver nitrate, which readily dissolves in dilute ammonia solution.

Correct Answer: D. Bitumen (Asphalt)

Explanation/Tip: Bitumen consists of heavy hydrocarbons with the highest molecular masses and highest boiling points, collected at the bottom of the fractional distillation column.

Correct Answer: D. Products have lower energy than reactants

Explanation/Tip: In an exothermic reaction, heat is released, meaning ΔH is negative and the energy of the products is lower than that of the reactants.

Correct Answer: A. Fehling’s solution

Explanation/Tip: Aldehydes are readily oxidized and give a brick-red precipitate of copper(I) oxide when warmed with Fehling’s solution. Ketones do not react.

Correct Answer: C. 6

Explanation/Tip: The coordination number refers to the number of ligand donor atoms directly bonded to the central metal ion. Here, there are six monodentate ammonia ligands.

Correct Answer: B. 0.1 M hydrochloric acid

Explanation/Tip: Hydrochloric acid is a strong acid that dissociates completely into ions in aqueous solution, resulting in high electrical conductivity.

Correct Answer: A. Efflorescence

Explanation/Tip: Efflorescence is the loss of water of crystallization from a hydrated salt to the atmosphere when exposed to air.

Correct Answer: C. Catalytic activity

Explanation/Tip: Transition metals and their compounds exhibit excellent catalytic activity due to their variable oxidation states and vacant d-orbitals.

Correct Answer: A. Methyl methanoate

Explanation/Tip: The alkyl group attached to oxygen is methyl (from methanol), and the acid portion has one carbon, making it methanoate.

Correct Answer: B. Ethyne (Acetylene)

Explanation/Tip: CaC₂ + 2H₂O → Ca(OH)₂ + C₂H₂. The hydrolysis of calcium carbide prepares ethyne gas.

Correct Answer: C. Boron trifluoride (BF₃)

Explanation/Tip: A Lewis acid is an electron-pair acceptor. Boron trifluoride has an incomplete octet (6 electrons around boron) and readily accepts an electron pair.

Correct Answer: B. Vanadium(V) oxide

Explanation/Tip: Vanadium(V) oxide (V₂O₅) is employed as the principal catalyst at 450°C for oxidizing sulfur dioxide in the Contact process.

Correct Answer: B. 2.65 g

Explanation/Tip: Molar mass of Na₂CO₃ = 106 g/mol. Moles = (0.10 × 250) / 1000 = 0.025 mol. Mass = 0.025 × 106 = 2.65 g.