JAMB Chemistry 2000

28 reviewed questions with answers and explanations.

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Question 2

Sieving is a technique used to separate mixtures containing solid particles of

  1. small sizes
  2. large sizes
  3. different sizes
  4. the same size
Answer and explanation

C: different sizes

A sieve separates particles by size. Smaller particles pass through its openings while larger particles are retained.

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Question 3

Which listed material contains aluminium, silicon, oxygen and hydrogen?

  1. Epsom salt
  2. Limestone
  3. Clay
  4. Urea
Answer and explanation

C: Clay

Clay commonly contains aluminosilicate minerals. Kaolinite, for example, has formula Al₂Si₂O₅(OH)₄, containing aluminium, silicon, oxygen and hydrogen. The other listed substances do not contain this set of elements.

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Question 4

50 cm³ of carbon monoxide reacts with 150 cm³ of air containing 20% oxygen by volume. Which reactant is in excess, comparing gas volumes at the same conditions?

  1. Carbon monoxide
  2. Carbon dioxide
  3. Oxygen
  4. Nitrogen
Answer and explanation

C: Oxygen

The air supplies 150 × 0.20 = 30 cm³ oxygen. From 2CO + O₂ → 2CO₂, 50 cm³ CO requires 25 cm³ oxygen. Therefore oxygen is in excess by 5 cm³. Nitrogen is not a reactant here.

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Question 6

The ratio of initial to final pressure of a fixed amount of gas is 1:1.5. What is its final volume if its initial volume is 300 cm³ at the same temperature?

  1. 120 cm³
  2. 200 cm³
  3. 450 cm³
  4. 750 cm³
Answer and explanation

B: 200 cm³

Boyle’s law gives P₁V₁ = P₂V₂ at constant temperature. Hence V₂ = (1/1.5) × 300 = 200 cm³. Higher pressure gives a smaller volume.

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Question 7

A gas sample has oxygen partial pressure 452 mmHg and total pressure 780 mmHg. What is the oxygen mole fraction?

  1. 0.203
  2. 0.579
  3. 2.030
  4. 5.790
Answer and explanation

B: 0.579

Dalton’s law gives mole fraction = partial pressure / total pressure. For oxygen this is 452/780 = 0.579 to three decimal places.

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Question 8

The fundamental difference between the three states of matter is the

  1. shape of their particles
  2. number of particles in each state
  3. shape of the container they occupy
  4. degree of movement of their particles
Answer and explanation

D: degree of movement of their particles

Particles in solids mainly vibrate around fixed positions; liquid particles can move past one another; gas particles move freely over much larger distances. Their freedom of movement distinguishes the states.

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Question 12

Knowledge of radioactive half-life can help to

  1. Create an element
  2. Detect an element
  3. Split an element
  4. Irradiate an element
Answer and explanation

B: Detect an element

A radioactive isotope has a characteristic half-life. Measuring decay and comparing it with known data can help identify or detect a radionuclide; knowing its half-life does not itself create, split or irradiate atoms.

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Question 13

The molecular shapes of CO₂, H₂O and CH₄, respectively, are

  1. Bent, linear and tetrahedral
  2. Bent, tetrahedral and linear
  3. Linear, bent and tetrahedral
  4. Tetrahedral, linear and bent
Answer and explanation

C: Linear, bent and tetrahedral

CO₂ has two electron-domain directions around carbon and is linear. H₂O has two bonds and two lone pairs around oxygen, giving a bent molecular shape. CH₄ has four bonding domains and is tetrahedral.

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Question 18

Which listed pollutant is a synthetic pesticide rather than a product of natural environmental processes?

  1. NO
  2. CO
  3. HCHO
  4. DDT
Answer and explanation

D: DDT

DDT is a manufactured organochlorine pesticide. Nitric oxide, carbon monoxide and formaldehyde can be produced by natural processes, whereas DDT contamination originates from its human manufacture and use.

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Question 20

Hydration of ions is associated with

  1. Absorption of heat
  2. Reduction of heat
  3. Conduction of heat
  4. Liberation of heat
Answer and explanation

D: Liberation of heat

When gaseous ions become surrounded by water molecules, favourable ion–dipole attractions form and energy is released. Hydration itself is exothermic, although dissolving an entire solid also requires energy to separate its lattice.

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Question 22

In HCl(aq) + H₂O(l) → H₃O⁺(aq) + Cl⁻(aq), what is Cl⁻ in relation to HCl?

  1. Conjugate acid
  2. Acid
  3. Conjugate base
  4. Base
Answer and explanation

C: Conjugate base

HCl donates a proton to water. The species left after that donation, Cl⁻, is the conjugate base of HCl; H₃O⁺ is the conjugate acid of water.

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Question 24

Using the ideal concentration model at 25 °C, what is the pOH of 0.25 mol dm⁻³ hydrochloric acid?

  1. 12.40
  2. 13.40
  3. 14.40
  4. 14.60
Answer and explanation

B: 13.40

For fully dissociated HCl, [H⁺] = 0.25 mol dm⁻³. Thus pH = −log₁₀(0.25) = 0.602 and, at 25 °C in the ideal dilute-solution model, pOH = 14.00 − 0.602 = 13.40.

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Question 25

Complete the reduction half-equation: MnO₄⁻(aq) + 8H⁺(aq) + Y → Mn²⁺(aq) + 4H₂O(l). What is Y?

  1. 2e⁻
  2. 3e⁻
  3. 5e⁻
  4. 7e⁻
Answer and explanation

C: 5e⁻

Manganese changes from +7 in MnO₄⁻ to +2, gaining five electrons. The balanced half-equation is MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O, with equal charge and atoms on both sides.

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Question 26

For the stoichiometric amounts in ½Zn²⁺(aq) + e⁻ → ½Zn(s), what charge is required to deposit ½ mol Zn? [F = 96,500 C mol⁻¹]

  1. 0.965 × 10⁴ C
  2. 4.820 × 10⁴ C
  3. 9.650 × 10⁴ C
  4. 48.200 × 10⁴ C
Answer and explanation

C: 9.650 × 10⁴ C

The half-equation uses one mole of electrons for half a mole of Zn. Its charge is therefore one Faraday: Q = 1 × 96,500 = 9.650 × 10⁴ C.

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Question 27

If M is deposited mass, Q is charge passed and Z is the electrochemical equivalent, how is Faraday’s first law written?

  1. M = Z/Q
  2. M = Q/Z
  3. M = Z/(2Q)
  4. M = QZ
Answer and explanation

D: M = QZ

Faraday’s first law states that deposited mass is proportional to charge. The electrochemical equivalent Z is mass deposited per unit charge, so M = ZQ. Its units give (g C⁻¹) × C = g.

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Question 29

For equal masses under the same conditions, powdered marble reacts faster with hydrochloric acid than granular marble because the powder has

  1. More molecules
  2. More atoms
  3. A larger exposed surface area
  4. A relatively larger mass
Answer and explanation

C: A larger exposed surface area

For the same mass, powder exposes a larger surface area to the acid than granules. More reacting surface is available at once, increasing the reaction rate.

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Question 30

Which rate-versus-concentration plot represents a zero-order reaction?

  1. A straight-line rise followed by a straight-line fall
  2. A horizontal line at a positive rate
  3. A straight line rising from the origin
  4. A curved rise that reaches a maximum and then falls
Answer and explanation

B: A horizontal line at a positive rate

A zero-order reaction has rate = k, independent of reactant concentration over the range where that rate law applies. Its rate-versus-concentration plot is therefore horizontal.

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Question 32

In the usual equilibrium-constant expression, which species contribute variable concentration or partial-pressure terms?

  1. Gaseous and solid species
  2. Liquid and solid species
  3. Solid and dissolved species
  4. Gaseous and dissolved species
Answer and explanation

D: Gaseous and dissolved species

In the usual concentration or pressure equilibrium expression, gaseous and dissolved species contribute variable terms. Pure solids and pure liquids have effectively constant activities and are absorbed into the equilibrium constant.

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Question 34

Which substance is commonly used for vulcanisation of rubber?

  1. Chlorine
  2. Hydrogen peroxide
  3. Sulfur
  4. Sulfuric acid
Answer and explanation

C: Sulfur

Sulfur creates cross-links between rubber polymer chains during vulcanisation. These links improve elasticity, strength and resistance to permanent deformation.

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Question 36

The characteristic fizz and sharp taste of soda water result from dissolved

  1. Carbon(IV) oxide
  2. Carbon(II) oxide
  3. Soda
  4. Glucose
Answer and explanation

A: Carbon(IV) oxide

Dissolved carbon dioxide produces the fizz and carbonic-acid contribution to the sharp taste of carbonated water. Carbon monoxide is not used for carbonation.

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Question 38

Synthesis gas is principally a mixture of

  1. CH₄ and H₂O
  2. CH₄ and H₂
  3. CO₂ and H₂
  4. CO and H₂
Answer and explanation

D: CO and H₂

Synthesis gas, or syngas, is a mixture principally of carbon monoxide and hydrogen. It is a feedstock for making fuels and chemicals such as methanol.

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Question 39

Potassium vapour burns with a

  1. Blue flame
  2. Brick-red flame
  3. Violet flame
  4. Golden-yellow flame
Answer and explanation

C: Violet flame

Potassium produces a characteristic lilac or violet flame. Heating excites electrons, and their return to lower energy levels emits characteristic wavelengths of light.

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Question 41

Haematite is an ore of

  1. Zinc
  2. Lead
  3. Iron
  4. Copper
Answer and explanation

C: Iron

Haematite is iron(III) oxide, Fe₂O₃, and is an important ore used to obtain iron.

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Question 42

According to the standard electrochemical reactivity series, which metal is least readily oxidised?

  1. Ca
  2. Na
  3. Zn
  4. Al
Answer and explanation

C: Zn

Zinc has a less negative standard reduction potential than aluminium, sodium or calcium, so it has the lowest thermodynamic tendency to be oxidised among these metals. Aluminium surface passivation affects reaction rate but does not place it below zinc in the reactivity series.

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Question 43

The repeating units of natural rubber are derived from which monomer?

  1. Alkynes
  2. Isoprene
  3. n-Propane
  4. Neoprene
Answer and explanation

B: Isoprene

Natural rubber consists mainly of cis-1,4-polyisoprene. Its chain units are derived from isoprene, 2-methylbuta-1,3-diene; polymerisation changes the monomer bonding while retaining the C₅H₈ composition per unit.

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Question 48

CH₃CH₂C(=O)OCH₂CH₃ is an

  1. Ether
  2. Ester
  3. Alkanal
  4. Alkanol
Answer and explanation

B: Ester

CH₃CH₂C(=O)OCH₂CH₃ contains the ester linkage –C(=O)–O– between carbon groups. It is ethyl propanoate, an ester.

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Question 49

Alkanones are generally obtained by controlled oxidation of

  1. Primary alkanols
  2. Secondary alkanols
  3. Tertiary alkanols
  4. Alkanoic acids
Answer and explanation

B: Secondary alkanols

Oxidation of a secondary alcohol removes the O–H hydrogen and the hydrogen on the carbon bearing OH, producing a ketone carbonyl. For example, propan-2-ol forms propanone.

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Question 50

Sucrose is made up of units of

  1. Glucose and glucose
  2. Glucose and fructose
  3. Fructose and fructose
  4. Galactose and glucose
Answer and explanation

B: Glucose and fructose

Sucrose is a disaccharide containing one glucose unit and one fructose unit joined by a glycosidic bond. Hydrolysis releases glucose and fructose.

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