JAMB Chemistry 2001

28 reviewed questions with answers and explanations.

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Question 2

What mass of water forms when 8.0 g hydrogen reacts completely with excess oxygen? [H = 1, O = 16]

  1. 72.0 g
  2. 36.0 g
  3. 16.0 g
  4. 8.0 g
Answer and explanation

A: 72.0 g

The equation 2H₂ + O₂ → 2H₂O gives one mole of water per mole of hydrogen. There are 8.0/2 = 4.0 mol H₂, giving 4.0 × 18 = 72.0 g H₂O.

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Question 4

A heating curve shows a solid warming, a melting plateau, liquid warming to 150 °C, a liquid–vapour plateau at 150 °C, then further warming of the vapour. If this vapour is cooled at the same pressure, at what temperature does condensation begin?

  1. 175 °C
  2. 250 °C
  3. 125 °C
  4. 150 °C
Answer and explanation

D: 150 °C

At the liquid–vapour phase change, temperature remains at the boiling point while latent heat is supplied. Cooling the vapour at the same pressure causes condensation at that same temperature, 150 °C.

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Question 5

Elements W, X, Y and Z have atomic numbers 2, 6, 16 and 20 respectively. Which is a metal?

  1. X
  2. Z
  3. W
  4. Y
Answer and explanation

B: Z

Atomic numbers 2, 6, 16 and 20 identify helium, carbon, sulfur and calcium respectively. Calcium, labelled Z, is the metal; the others are non-metals.

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Question 6

Two identical atoms, each with one unpaired outer-shell electron, approach and form overlapping outer shells containing a shared pair, with one electron contributed by each atom. Which bond is formed?

  1. A metallic bond
  2. A covalent bond
  3. An electrovalent bond
  4. A coordinate covalent bond
Answer and explanation

B: A covalent bond

Each atom supplies an electron to a shared pair. Sharing an electron pair forms an ordinary covalent bond. A coordinate covalent bond would have both shared electrons supplied initially by one atom.

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Question 9

Which statement about the average kinetic energy of ideal-gas molecules is correct?

  1. It increases whenever pressure increases
  2. It increases as absolute temperature increases
  3. It increases whenever volume increases
  4. It necessarily increases at constant pressure
Answer and explanation

B: It increases as absolute temperature increases

For an ideal gas, average translational kinetic energy per molecule is 3kT/2. It increases with absolute temperature. Pressure or volume changes alone do not imply a change in that average energy.

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Question 10

Millikan’s contribution to atomic theory was determining the

  1. Positive rays
  2. Cathode rays
  3. Charge-to-mass ratio of the electron
  4. Charge on the electron
Answer and explanation

D: Charge on the electron

Millikan’s oil-drop experiment measured the elementary electric charge. The charge-to-mass ratio of the electron had been measured earlier using cathode rays.

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Question 13

Which chemical is used for coagulation during water purification?

  1. Copper(II) sulfate
  2. Sodium sulfate
  3. Aluminium sulfate
  4. Calcium sulfate
Answer and explanation

C: Aluminium sulfate

Aluminium sulfate is a coagulant. In suitable water conditions it forms aluminium hydroxide flocs that gather fine suspended material so it can be removed by settling and filtration.

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Question 15

White phosphorus is stored under water to prevent it from

  1. Smelling
  2. Dehydrating
  3. Catching fire
  4. Becoming inert
Answer and explanation

C: Catching fire

White phosphorus can ignite in air. Storing it under water limits contact with oxygen and prevents ignition; this storage precaution refers to white phosphorus rather than all phosphorus allotropes.

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Question 16

Which separation process recovers a pure solvent from a solution containing a non-volatile solute?

  1. Evaporation
  2. Extraction
  3. Condensation
  4. Distillation
Answer and explanation

D: Distillation

Distillation vaporises a solvent and then condenses the vapour into a separate receiver. Non-volatile dissolved substances remain behind, allowing recovery of the solvent.

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Question 19

Suitable deliquescent substances are used for

  1. Drying
  2. Melting
  3. Wetting
  4. Cooling
Answer and explanation

A: Drying

Deliquescent substances absorb enough moisture from air to dissolve in the absorbed water. Suitable examples such as calcium chloride can remove water vapour and serve as drying agents.

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Question 20

What decrease in volume occurs when excess alkaline pyrogallol completely absorbs oxygen from 30.00 cm³ dry air containing 21% oxygen by volume, at unchanged temperature and pressure?

  1. 0.63 cm³
  2. 0.06 cm³
  3. 15.00 cm³
  4. 6.30 cm³
Answer and explanation

D: 6.30 cm³

Alkaline pyrogallol absorbs oxygen. Taking dry air as 21% oxygen by volume, the removed volume is 0.21 × 30.00 = 6.30 cm³, with temperature and pressure unchanged.

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Question 22

In 3Cu(s) + 8HNO₃(aq) → 3Cu(NO₃)₂(aq) + 4H₂O(l) + 2NO(g), copper acts as

  1. A base
  2. An oxidising agent
  3. A reducing agent
  4. An electron acceptor
Answer and explanation

C: A reducing agent

Copper changes from oxidation state 0 to +2, losing electrons. It supplies the electrons that reduce nitrogen from +5 in nitrate to +2 in NO, so copper is the reducing agent.

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Question 23

For NH₃(g) + HCl(g) → NH₄Cl(s), the entropy change of the system is

  1. Zero
  2. Indeterminate
  3. Positive
  4. Negative
Answer and explanation

D: Negative

Two gaseous reactants form a crystalline solid. The loss of gas-particle freedom gives a decrease in the system’s entropy, so ΔS is negative.

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Question 26

For a dilute electrolyte at fixed temperature, reducing concentration generally makes its electrical conductivity

  1. Decrease
  2. Increase
  3. Become exactly zero
  4. Remain unchanged
Answer and explanation

A: Decrease

In a dilute electrolyte, reducing concentration lowers the number of mobile charge carriers per unit volume, so electrical conductivity decreases at fixed temperature. Molar conductivity is a different quantity and can increase on dilution.

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Question 30

For P(g) + Q(g) ⇌ 3R(s) + S(g), which change necessarily increases the equilibrium yield of R under otherwise unchanged conditions?

  1. Removing some S
  2. Using a larger closed vessel
  3. Adding a catalyst
  4. Increasing the temperature
Answer and explanation

A: Removing some S

Removing gaseous product S lowers the reaction quotient and drives the equilibrium forward, forming more R. Increasing vessel volume favours the side with more gas molecules, which is the reactant side; a catalyst does not change equilibrium yield.

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Question 33

Which half-equation represents reduction?

  1. 2O²⁻ → O₂ + 4e⁻
  2. Fe²⁺ → Fe³⁺ + e⁻
  3. 2H⁺ + 2e⁻ → H₂
  4. Cr → Cr²⁺ + 2e⁻
Answer and explanation

C: 2H⁺ + 2e⁻ → H₂

Reduction is electron gain. Hydrogen ions gain two electrons to form H₂, reducing hydrogen’s oxidation number from +1 to 0. The other half-equations release electrons and represent oxidation.

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Question 34

When ΔH is negative, a reaction is described as

  1. Endothermic
  2. Exothermic
  3. Reversible
  4. Ionic
Answer and explanation

B: Exothermic

A negative enthalpy change means the products have lower enthalpy than the reactants and heat is released to the surroundings. Such a reaction is exothermic.

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Question 36

Proteins heated with aqueous acid undergo

  1. Polymorphism
  2. Hydrolysis
  3. Fermentation
  4. Substitution
Answer and explanation

B: Hydrolysis

Acid-catalysed hydrolysis breaks peptide bonds by reaction with water. Prolonged heating with acid can break a protein down into its constituent amino acids.

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Question 37

Alcoholic fermentation is the

  1. Breakdown of carbohydrate to glucose
  2. Breakdown of sugar to carbohydrate
  3. Conversion of sugar to alcohol in the presence of yeast
  4. Conversion of alcohol to sugar in the presence of yeast
Answer and explanation

C: Conversion of sugar to alcohol in the presence of yeast

In alcoholic fermentation, yeast enzymes convert sugars such as glucose into ethanol and carbon dioxide under anaerobic conditions: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.

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Question 38

Complete catalytic hydrogenation of benzene produces

  1. Cyclohexene
  2. Oil
  3. Margarine
  4. Cyclohexane
Answer and explanation

D: Cyclohexane

Complete catalytic hydrogenation adds three molecules of H₂ to each benzene molecule: C₆H₆ + 3H₂ → C₆H₁₂. The saturated ring product is cyclohexane.

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Question 40

When chlorine is passed into water and the resulting chlorine water is exposed to sunlight, the final products are

  1. Chlorine gas and hydrogen
  2. Hydrochloric acid and oxygen
  3. Chlorine gas and hypochlorous acid
  4. Oxygen and hypochlorous acid
Answer and explanation

B: Hydrochloric acid and oxygen

Chlorine initially reacts with water to form HCl and HClO. Sunlight decomposes hypochlorous acid: 2HClO → 2HCl + O₂. The overall products are hydrochloric acid and oxygen.

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Question 41

Which pair consists of structural isomers?

  1. But-1-ene and but-2-ene
  2. Ethanol and propanone
  3. Trichloromethane and tetrachloromethane
  4. Benzene and methylbenzene
Answer and explanation

A: But-1-ene and but-2-ene

But-1-ene and but-2-ene both have molecular formula C₄H₈ but differ in double-bond position. The other pairs have different molecular formulas and are not isomers.

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Question 43

During vulcanisation of rubber, sulfur is added to

  1. Lengthen individual rubber chains
  2. Break down the rubber polymer
  3. Act as a catalyst
  4. Bind rubber chains together
Answer and explanation

D: Bind rubber chains together

Sulfur forms cross-links between rubber chains. These links restrict chain slippage and improve the useful elastic and mechanical properties of rubber.

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Question 44

When sodium reacts with water, the resulting solution is

  1. Alkaline
  2. Acidic
  3. Neutral
  4. Weakly acidic
Answer and explanation

A: Alkaline

Sodium reacts with water to give sodium hydroxide and hydrogen: 2Na + 2H₂O → 2NaOH + H₂. Hydroxide ions make the resulting solution alkaline.

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Question 45

The condensed general formula for alkanals is

  1. RCOOR′
  2. R₂CO
  3. RCHO
  4. ROH
Answer and explanation

C: RCHO

Alkanals contain a terminal –CHO group, so their condensed general formula is RCHO. R is an alkyl group, or hydrogen in methanal.

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Question 46

Which listed metal gives a brick-red flame?

  1. Ca
  2. Na
  3. Mg
  4. Pb
Answer and explanation

A: Ca

Calcium gives a brick-red flame in the characteristic flame test. Magnesium burns with an intense white light, while sodium gives a strong yellow flame.

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Question 47

Which gas is best collected by downward displacement of air?

  1. Chlorine
  2. Sulfur(IV) oxide
  3. Carbon(IV) oxide
  4. Ammonia
Answer and explanation

D: Ammonia

Ammonia is less dense than air and very soluble in water. It rises into an inverted gas jar and pushes air downwards, so downward displacement of air is suitable.

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Question 49

The principal gangue impurity removed by lime in the conventional blast-furnace extraction of iron is

  1. Calcium silicate
  2. Silicon(IV) oxide
  3. Sulfur(II) oxide
  4. Carbon(IV) oxide
Answer and explanation

B: Silicon(IV) oxide

Silica, SiO₂, is a common gangue impurity in iron ore. Calcium oxide from limestone reacts with it to form calcium silicate slag, removing it from the iron.

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